F-35 Lightning II

In 1995, when the JSF requirements were developed, the Air Force was seeking an aircraft that would perform the job of the F-117 while remedying its shortcomings. At the time, the service was also expected to buy some 442 F-22s to defeat any potential aerial threat. The requirement was built around the F-117's internal load and then added a radar, GPS-guided weapons for all-weather attack and an electronic warfare suite capable of detecting, identifying and avoiding pop-up...

2009

Thermal problems were discovered in March 2009. First identified during hot-weather ground operations, the fuel-air heat exchanger was apparently not providing sufficient cooling. Officials said that hot weather activity would be limited to deal with the problem in the short term. The F-35 dumps the heat generated from electronics and other systems, including the electrically powered actuators, into the fuel, where it is dissipated as the fuel is burned. The problem could be fixed with larger, more efficient heat exchangers and other changes, including a new fuel pump then being developed. The new fuel pump was expected to be fitted on LRIP Lot 3 aircraft.

On March 12, 2009, the U.S. Government Accountability Office (GAO) issued a report saying that development of the F-35 would likely take longer and cost more than estimated, even as the Pentagon was seeking to accelerate production. Two recent estimates cited by the report projected additional costs between US$2.4 billion and US$7.4 billion and an additional one to three years to complete development. The Pentagon at the time wanted to accelerate F-35 procurement by 169 aircraft from fiscal 2010 through fiscal 2015, which could require an additional US$33.4 billion in funding over those years. The plan to procure hundreds of aircraft through cost-reimbursement contracts also magnified the financial risk to the government, the GAO said.

At the same time, Lockheed Martin was still correcting manufacturing inefficiencies and parts problems that had significantly delayed the delivery of test assets. Manufacturing schedules had been extended three times and only two of 13 test aircraft were delivered, according to the report. Officials expected to deliver all test aircraft and fix many problems by 2010, by which time the Pentagon wanted to purchase 62 operational aircraft and ramp up procurement. The GAO noted that "procuring large numbers of production jets while still working to deliver test jets and mature manufacturing processes does not seem prudent, and looming plans to accelerate procurement will be difficult to achieve cost effectively."

The Dept. of Defense in late 2007 decided to reduce test aircraft and flight testing increasing risk. Revised test plans called for simulation labs, a flying test bed and desk studies to verify 83 percent of the F-35's capabilities, with only 17 percent to be verified through test flights. However, the ability to substitute to such a degree for flight testing had not yet been demonstrated, the GAO said. Under the accelerated procurement plan, the Pentagon could buy up to 360 aircraft at a cost of US$57 billion before completing development flight testing.

In April 2009, Israel was said to be reconsidering plans to buy F-35 fighters due to the unexpectedly high cost and disagreements with Lockheed over the installation of Israeli systems in the aircraft. Negotiations had stalled over Israeli air force demands that its aircraft come with unique communications, controls and electronic systems and be modified to carry Israeli weaponry. Such modifications would reportedly increase the price by around 25 percent. Israel said it wanted to integrate its Blue Cedar C4I system as well as some rewiring to accommodate electronic warfare systems in apertures Band 2 and Band 5 in the belly and wings of the aircraft. There were also plans to install an external electronic warfare pod.

The U.S. reportedly refused to allow Israel access to the F-35's internal mainframe citing concerns that it would enable the Israeli air force to obtain classified technology. Israel argued that it needed the ability to repair damaged or broken computer systems in real time and could not wait for a computer system to be sent to the U.S. for repairs in the midst of a war. U.S. officials said that a number of spare computer systems would be provided, and damaged computers would need to be sent back for repairs. The disagreements led the Israeli government to ask Boeing for details on its new F-15 Silent Eagle fighter. These issues were ultimately resolved and Israel has ordered 50 of the aircraft.

On April 21, 2009, it was reported that hackers had penetrated the F-35 program and were able to steal terabytes of data related to the aircraft's design and electronic systems. Officials said that the most sensitive information relating to the program was likely safe, since it was stored on computers not connected to the internet. Some reports indicated that the attack probably originated in China. Security breaches reportedly occurred as early as 2007, with some taking place in F-35 partner countries such as Turkey. The Pentagon and Lockheed Martin later attempted to discount the story.

A report on the F-35 program in Jane's Defence Weekly dated June 10, 2009, outlined some of the concerns about the project. Analysts noted that Lockheed implemented a highly aggressive production strategy that included the construction of production aircraft before flight testing was completed. If production plans ran into problems, it could diminish the U.S. military's combat aviation edge as legacy aircraft continued to age. There were also said to be technical risks with the program, including reliance on more than 20 million lines of code, which must fuse sensor data in a threat environment that includes cyber warfare.

Some critics also said that the aircraft was over-built for irregular warfare and too short-ranged to operate effectively in a high-end missile-threat environment, according to the report. The US$300 billion wrapped up in the program took away from funds that could be used to buy more specialized aircraft. Proponents said that the F-35's stealth characteristics and increased internal fuel capacity provided a significant improvement over legacy fighters such as the F-16 . At the same time, the aggressive production schedule was necessary to ensure on-time delivery, lower costs and begin replacing legacy aircraft. The F-35 was expected to reach its peak production rate of about 250 aircraft a year in 2015, which would ensure quicker delivery and increase economies of scale. The report noted that there was a risk of customers reducing their planned aircraft acquisitions or cancelling orders altogether. There were also no guarantees that Congress would buy all of the aircraft planned or at the desired production rate. Changes in planned aircraft quantity and rising labor and metal costs had already contributed to a 38 percent increase in the F-35 unit cost since 2001.

In July 2009, the House Armed Services Committee, in its markup of the fiscal 2010 defense authorization, noted that Pratt & Whitney's F135 engine development program had overrun its expected development costs by 38 percent, or US$1.87 billion in then-year dollars, since the beginning of the program. The F-35 program manager also reported an increase of between 38 percent and 43 percent in F135 engine procurement costs between December 2005 and December 2008, as the program began to make the transition into production. The increase for the F-35B STOVL aircraft was 47 percent due to larger overruns in the cost of producing the lift system. The committee also noted that the General Electric F136 engine had not experienced any cost growth since its inception. The report was part of an ongoing debate in Washington over the value of the program to develop a second engine, the F136, for the F-35. The Obama administration threatened to veto any authorization that included funding for the second engine.

GE researchers maintained that the F136 engine, with its larger combustor had greater potential for increased power as it matured over its lifetime than the F135. Ultimately, the F136 project was terminated.

The Pentagon formed a Joint Assessment Team by mid-2009 to investigate concerns about increases in the projected cost of the Pratt & Whitney F135 engine. At the time, program officials warned that the engine appeared to be headed for higher-than-budgeted costs.

In August 2009, Brig. Gen. David Heinz, the F-35 program officer, noted several new concerns about the F135 engine. He said that the engine had too many individual blades that failed to meet specifications and combined "stack-ups" of blades that failed early. The general said that Pratt & Whitney must also reduce the cost of each engine, which was US$8.3 million at the time. Heinz also said that the program had not realized the expected benefits from dual-sourcing the engine, because Pratt & Whitney had not felt compelled to compete on equal terms with the General Electric/Rolls-Royce F136 engine.

2011

On Jan. 6, 2011, Defense Secretary Robert Gates announced another restructuring of the F-35 program as part of a wider cost-reduction plan. The new plan was expected to save about US$4 billion over the following five years. Gates said work on the F-35A and F-35C was progressing satisfactorily, but placed the F-35B on a two-year probation and said it could be cancelled if Lockheed was unable to fix numerous test problems.

Gates also said that issues with the F-35B could lead to a redesign of the aircraft's structure and propulsion. Issues included lift-fan clutch heating; driveshaft thermal expansion; roll-post heating; lift-fan doors; bulkhead cracking; and pilot-vehicle interface issues.

Lockheed officials said lift-fan clutch heating had been addressed by adding a passive cooling circuit to provide cooling air to the clutch in up-and-away flight when the forced-cooling fan used in STOVL mode is turned off. Pratt & Whitney said that the lift-fan clutch and roll-post actuators could get too warm in certain flight conditions "because the environment surrounding the hardware is more demanding than in the original design." Sensors were installed to monitor temperatures. The heating was caused by drag between plates when disengaged. When alerted to high temperatures, the pilot could climb to 10,000 ft (3,000 m) until the clutch cooled, according to company officials.

Heating of the roll-post actuator was caused by hot engine air leaking as the roll nozzle seals aged. Insulation was added. Lockheed said that the driveshaft was also redesigned with a new bellows coupling to accommodate greater than predicted variations in length resulting from airframe and propulsion system build tolerances, thermal and pressure growth and maneuver deflection.

Cracking of the fuselage bulkhead was addressed by thickening the bulkhead for production aircraft and by machining smoother curves on bends in corners in two small areas of the bulkhead to eliminate stress concentrations on assembled aircraft.

The helmet-mounted display was also failing to meet night-vision performance goals. Potential fixes included higher-sensitivity helmet-mounted cameras, higher-resolution display projectors and improved optics.

A Pentagon document outlining the changes called for production of 325 F-35s through fiscal 2016 instead of the 449 that were planned. Cutting those 124 planes could save more than US$10 billion, about US$4.6 billion of which was to be shifted to cover more testing and offset overly optimistic cost estimates, defense officials said. The Pentagon estimated that it would cost another US$13.8 billion to finish development on top of the US$37 billion already spent.

The restructuring included revamped flight testing and software development using industry-standard productivity rates. It added 2,000 flights to the program for a total of 7,800, just 600 of which had been completed by February 2011. The program added sorties for test-pilot training and built a 500-flight margin for unexpected issues. Development testing was also extended to October 2016. The final software standard, Block 3C, was scheduled to be released for flight testing in June 2015. At the time, about 4 million of the 8 million lines of code had been completed, according to Air Force program officials.

Software development was also moved to the Block 1 standard ahead of schedule after numerous issues were discovered with the Block 0.5 software. Flight testing of Block 1A was underway and Block 1B was scheduled to be loaded in June 2011 and released to production aircraft by the end of that year. Block 2 was being developed in two stages, with Block 2A to begin flight testing in November 2011 and Block 2B in September 2012. Flight trials were to continue through 2014 and then Block 3 software would be released in three phases: A, B and C.

A report by the Office of the Director of Operational Test and Evaluation (DOT&E) in January 2011 indicated that the F-35A and F-35B variants experienced "transonic wing roll-off, [and] greater than expected sideslip during medium angle-of-attack testing." Various components used were also shown to be less reliable than expected. The report also noted that the F135 engine had encountered afterburner "screech," in which airflow disruptions caused severe vibrations that prevented the engine from reaching maximum power. That problem delayed some testing and efforts were underway to fix it, officials said. The solution included minor hardware changes to the fuel system, reduced aerodynamic leakages and upgraded software.

There were also problems with the helmet-mounted display, which had to be resolved before the Block 2 mission system software could be tested. The DOT&E report called for the Block 3 mission system software to be tested on a simulated battlefield because existing test ranges were not adequate to test the F-35's sensor arrays. It also said that the onboard inert gas-generation system (OBIGGS) failed to inert the fuel tank ullage spaces and should be redesigned.

On May 4, 2011, Bloomberg News reported that the Defense Contract Management Agency (DCMA) had told congressional investigators that it had found difficulties with Lockheed's manufacturing of the aircraft's outer surface or "mold line." A GAO report noted that the "inability to meet the outer mold line requirements could have major impacts on cost as well as stealth requirements and capabilities." The process involves detailed attention to the skin's finish, fasteners and drain holes that affect an aircraft's radar-evading profile. The problem was not expected to be resolved until around June 2015, after which a large number of aircraft would have to be retrofitted for any design changes. A Lockheed spokesman said that all F-35s were meeting requirements and that manufacturing improvement processes were in place to address tolerance challenges.

All 20 U.S. F-35s were grounded on Aug. 2, 2011, after a failure of the aircraft's integrated power package (IPP). Aircraft AF-4 suffered the failure during a ground maintenance run at Edwards AFB. The crew shut down the aircraft after the failure and the incident was placed under review. The IPP combines the functions of an auxiliary power unit, emergency power system and environmental controls. On Aug. 10, military officials authorized the F-35 to resume ground testing, but not flight testing.

The investigation found that a control valve problem caused the IPP failure, but a reason for the valve failure and a solution had not yet been determined. The valve allows the IPP to switch its power source from combusted air to bleed-air after it has started up the F-35's engine. Highly compressed air built up after the valve failed to open, producing what was described as an "explosive event" by program officials. The Pentagon cleared the F-35 test fleet to resume flight operations on Aug. 18. The production jets were authorized for flight again on Aug. 24, 2011.

Defense News reported on Sept. 1, 2011, that technicians with the F-35 program had found and fixed a problem with part of the aircraft's wing structure. During structural testing, a shortfall in the predicted durability of the F-35A and F-35B wing forward root rib was identified. The root rib is an aluminum part located where the leading edge of the wing meets the fuselage. Requirements called for the part to have a life of 8,000 hours and it was scheduled to be tested to 16,000 hours. However, the root rib developed cracks after 2,800 hours. The crack had been foreseen and was discovered to be consistent with the analytical prediction, program officials said.

Retrofit plans as well as a redesigned full-life forward root rib for both variants were developed, said the officials. The affected F-35s were to be inspected regularly until they were retrofitted with the fix. The new design was scheduled to be incorporated into production planes beginning with LRIP-5 F-35A and F-35B aircraft. A total of 30 F-35A and 34 F-35B LRIP aircraft needed to be modified.

Lockheed Martin awarded BAE Systems a contract for Q-Sight helmet-mounted displays (HMDs) on Oct. 10, 2011, with detachable night-vision goggles for the F-35 program. The HMD, to be delivered beginning in 2012, would enable all aspects of flight operations. The helmets were also fitted with an optical head-tracking system that allowed pilots to aim weapons and navigate by looking in a particular direction. The BAE Systems HMD was ordered after numerous issues with the original Vision Systems International (VSI) system with an integrated night-vision capability.

In October 2011, Vision Systems International (VSI) officials said an initial fix for the F-35's helmet-mounted display would be delivered in mid-2012 with a final version to be completed within two years. HMD problems included a jittery display, high image latency and a night-vision system that did not meet Marine requirements. The first package of fixes was expected to take care of all save the night-vision problems, according to VSI. It included software adjustments and the addition of an inertial motion unit to filter out ejection-seat vibrations.

To fix the night-vision problems, VSI said it would replace the ISIE-10 low-light camera with a new ISIE-11 camera, which should produce images comparable to or better than night-vision goggles. Lockheed officials said they would add a second ISIE-11 camera to the cockpit glare shield to compensate for any obstructed views caused by the canopy bow. Imagery from the helmet and glare-shield cameras would be fused seamlessly and presented to the pilot on the visor, according to VSI. In addition, an optical head-tracker was to be added for better accuracy and the software and hardware modified to tie the various elements together. Lockheed officials said that digital imagery from the distributed aperture system (DAS ) was not yet sharp enough to meet requirements and was contributing to the night-vision issues.

In November 2011, it was reported that three out of five F-35B STOVL development aircraft had experienced tiny cracks in a lift fan-related component which prevented the aircraft from reconfiguring in flight and landing vertically. Test aircraft BF-1 and BF-2 were being modified with a redesigned actuator support beam at the time, according to program officials. Cracks had also been found in BF-4, which was restricted to conventional flight until the part could be modified. The potential for cracks to develop in the actuator support beam had been identified several years ago, officials said.

A redesigned beam was installed on the fifth STOVL test aircraft during final assembly, officials said. BF-3 had fewer flight hours, but was only flown in the conventional mode after the cracks were discovered. The impact on the flight-test program was expected to be minor. The cracks were discovered about a month after BF-2 and BF-4 completed a series of shipboard vertical landings on USS WASP .

The Pentagon submitted a quick-look review for the F-35 program on Nov. 29, 2011. The review revealed that there were five major issues with the program, one of which remained classified. Analysts said that problem was likely related to the aircraft's stealth characteristics. Other issues included the helmet-mounted display. A simpler, alternative HMD was ordered from BAE Systems in September 2011, but did not meet the requirement for "through the airplane" zero-light visibility provided by the electro-optical distributed aperture system (DAS ). The problem was said to be latency: the image in the helmet lagged 130 milliseconds behind sightline movement, where the specifications called for 40 ms. The system could not be fixed without changing the fighter's integrated core processor and the DAS sensors. The backup helmet also suffered from buffet and latency issues for symbology, said the review.

The underwing fuel dump system also failed to get fuel clear of aircraft surfaces, allowing fuel to accumulate in the flaperon and potentially seep into the IPP exhaust, potentially creating a fire hazard. The IPP was also shown to be unreliable. Intended to last for 2,200 hours, 16 IPPs had already been removed and replaced during flight testing. The report also predicted more problems in the future.

2013

On Jan. 14, 2013, Bloomberg News reported that the F-35 fell short of meeting its test objectives in 2012, despite flying more sorties than planned. "The lag in accomplishing the intended 2012 flight testing content" would "contribute to the program delivering less capability in production aircraft in the near term," said Michael Gilmore, the Pentagon's test director in an annual report to Congress. The 1,092 test flights through November 2012 exceeded the planned rate and the aircraft met 4,711 of the specific goals set for the year. It fell about 28 percent short of completing those test points, according to Gilmore. "Certain test conditions were unachievable due to unresolved problems and new discoveries," said the report. The need for repeat testing of fixes on the aircraft "displaced opportunities to meet flight test objectives."

The report also said that F-35 test flights were not allowed within 25 mi (40 km) of known lightning conditions due to a need to redesign the onboard inert gas-generating system (OBIGGS), which maintains correct oxygen levels in the fuel tank. The system is vital to protecting the engine from exploding in case of a lightning strike. A poor design for the fuel tank venting system also meant that when the jet was below 20,000 ft (6,100 m), its descent rate was limited to no more than 6,000 ft/min (1,800 m/min). Neither restriction was acceptable for combat or combat training, the report said.

Gilmore noted several challenges confronting the program. The F-35 was already close to its planned maximum weight, leaving little room for additional parts to improve reliability and performance. The report also revealed that durability testing for the F-35B had been halted in December 2012 after multiple cracks were discovered. Cracks were found on the right wing and engine of the F-35A, and multiple cracks on the bulkhead flange of the F-35B. This discovery would require mitigation plans, possibly including redesigning parts and additional weight, according to the report.

Time magazine's Battleland blog reported on Jan. 11, 2013, that two changes designed to reduce the F-35's weight by 11 lb (5 kg) had made it 25 percent more vulnerable to exploding in mid-air and other possible problems. Testing demonstrated that removing 9 lb (4 kg) of fueldraulic fuses and 2 lb (0.9 kg) of coolant shutoff valves "results in a 25 percent increase in aircraft vulnerability," according to the report. The blog reported that designers were reconsidering the modifications.

Flight International reported on Jan. 14, 2013, that the Pentagon was reducing performance requirements for the F-35, citing the DOT&E report. Specifications for all three variants for transonic acceleration and sustained turn rates had been reduced. The F-35C had reduced turn performance from 5.1 to 5 sustained gs and increased the time for acceleration from Mach 0.8 to Mach 1.2 by at least 43 seconds. The changes were the result of aircraft performance and flying qualities evaluations, according to the report. The time for acceleration for the F-35A had increased by 8 seconds, while the F-35B's increased by 16 seconds. Sustained turning for the F-35B was reduced from 5g to 4.5g, while the F-35As was reduced from 5.3g to 4.6g.

All variants were also experiencing problems with their horizontal tails, including higher than expected temperatures during sustained high-speed/high-altitude flight resulting in delamination and scorching of the surface coatings and structure, the report said.

The F-35B and F-35C continued to have issues with transonic roll-off and buffeting. The F-35B had received vehicle systems software to reduce rudder and flaperon hinge movement in the transonic/supersonic region. Transonic buffeting was more severe on the F-35C due to its larger wing. The program planned to examine how to reduce its impact with the use of wing spoilers, but detailed test plans had not been completed.

The Pentagon report also noted that the helmet-mounted display was still having problems with jittery images and was not meeting specifications for night-vision acuity. A new problem was discovered with light from cockpit avionics displays leaking into the helmet-mounted display, degrading visual acuity. Image latency, however, was now within tolerances of 133 milliseconds, below the human factors derived maximum of 150 milliseconds, but additional testing was needed, the report said.

F-35 software was still in a poor state, the report found. The initial Block 1 software package was not complete, with 20 percent remaining to be delivered and flight tested. An initial version of the more advanced, although not combat capable, Block 2A software had been delivered four months late. Eight subsequent versions had been released to flight test, but with less than 50 percent of the full, planned Block 2A capability. The program made little progress in the development, integration and laboratory testing of any software beyond Block 2B, the report said. Block 3I software, required for delivery of Lot 6 aircraft and hosted on an upgraded processor, lagged in integration and laboratory testing.

Flight International on Jan. 17, 2013, reported Lockheed's response to the Pentagon report. Company officials did not dispute the findings of the study, but said that many of the problems had already been addressed. Such problems were what one would expect to find during flight testing, they said. Officials also said the flight test program was about 5 percent ahead of the plan and that development was on track to be completed in 2016.

Lockheed said that concurrency costs -- the cost of implementing modifications as a result of design changes -- were starting to decline. Officials said that the issue of cracking on a bulkhead flange on the underside of the F-35B fuselage during a 7,000-hour inspection was being fixed. Lockheed had found and implemented a solution with a "single digit weight impact," said the business development director. Officials also said that weight margin on the F-35B had increased by around 100 lb (45 kg) to more than 400 lb (181 kg).

Company officials said that Block 1 software had been delivered and was performing well. The Block 2A software had been delivered for testing and was expected to be provided to Eglin AFB later in the year for training. This software block would enable instructors to use the aircraft's radar, electronic warfare suite and infrared sensors and simulate weapon releases.

Issues with aerodynamic heating on the horizontal tail surfaces of the F-35 at high altitudes and high speeds were also reportedly being resolved. The tail coatings were being damaged by friction with the air and heat from the afterburner. New coatings were already being implemented for the F-35A, with testing for a fix underway for the other two models.

Lockheed also discovered the root cause of problems with the weapons bay doors, with a fix prepared and ready for testing. Transonic roll-off issues, which manifests as uncommanded rolls at high subsonic speeds and high angles of attack, were addressed with adjustments to the flight-control schedule software for the F-35A and F-35B. A similar fix was being implemented for the F-35C, but wing spoilers might still be needed, the officials said. Aviation Week, however, reported that testing demonstrated that control-law software changes were sufficient to mitigate transonic roll-off issues. Accordingly, the pop-up spoilers added to the F-35C had been removed from production aircraft.

Flight International on Jan. 30, 2013, reported that the Pentagon's decision to reduce the performance specifications for all three F-35 models could have a significant operational impact. According to experienced fighter pilots consulted by the magazine, the reductions mean the F-35 will not be "anywhere near the performance of most fourth-and fifth-generation aircraft."

At higher altitudes, the reduced performance would impact survivability against advanced surface-to-air missile systems, such as the SA-20 Gargoyle ** (S-300PMU2 ). At lower altitudes, reduced airframe performance would put pilots at greater risk against shorter-range surface-to-air missiles and anti-aircraft artillery. The F-35C's reduced transonic acceleration capabilities would increase gas consumption and negatively impact tactical execution.

To compensate for the reduced performance, pilots would have to rely on the fighter's stealth characteristics and sensors, according to sources familiar with the aircraft. Engagement zones and maneuvering ranges would likely have to be driven further out against the most dangerous surface-to-air threats.

For aerial engagements, tactics would need to be developed to emphasize stealth and beyond-visual-range combat. If visual-range combat becomes necessary, pilots would need to make every effort to enter the "merge" from an advantageous position, which should be possible as a result of the F-35's stealth characteristics. Once engaged, turning should be minimized in favor of using the fighter's AAQ-37 distributed aperture system, helmet-mounted display and high off-boresight missiles to engage enemy aircraft.

If a turning fight is unavoidable, the F-35 has good instantaneous turn performance and good high angle-of-attack (50-degree AoA limit) performance. The F-35 is in this way comparable to the F/A-18 Hornet , so pilots could use similar tactics, according to the sources.

The Pentagon cleared the F-35B to return to flight on Feb. 12, 2013, reported Flight International. The aircraft had been grounded on Jan. 18, 2013, after a fueldraulic hose failure. An investigation determined that the hose was improperly crimped, according to the F-35 Joint Program Office. The fueldraulic hose powers the actuator movement for the F-35B's STOVL thrust vectoring exhaust system. Hoses on all 25 F-35B aircraft in U.S. Marine Corps and British service were inspected, with seven found to have the manufacturing defect. Those aircraft would be cleared to return to flight once new hoses were installed, said the program office.

Reuters reported on March 9, 2013, that a draft report from the Government Accountability Office (GAO) indicated that the cost of retrofitting F-35s to rectify problems found in flight testing would reach more than US$1.7 billion. Rework would add about US$900 million to the cost of the first four lots, plus about US$827 million over the next six batches, the GAO report said.

Cost overruns on the 63 aircraft built in the first four production batches were expected to reach US$1.2 billion, with the government responsible for about US$756 million. The report said overruns were declining as production costs fell and that Lockheed was delivering the jets faster.

The GAO said that the F-35 program was overall "moving in the right direction after a long, expensive and arduous learning process ... Going forward, ensuring affordability -- the ability to acquire aircraft in quantity and to sustain aircraft over the life cycle -- is of paramount concern."

The final report indicated concerns with long-term procurement and sustainment costs of the F-35. Current plans would require the Pentagon to spend about US$12.6 billion annually through 2037. The unit cost of the aircraft would also rise if the Dept. of Defense reduced its planned procurement of 2,443 F-35s or foreign partners reduced their plans for 697 aircraft. The Pentagon's Cost Analysis and Program Evaluation office calculated that average cost of the plane, which had reached US$137 million, would rise by 6 percent if all 697 foreign orders were cut, or 9 percent if Washington reduced its buy to 1,500 jets and the foreign partners maintained their orders. The cost would jump 19 percent if the U.S. bought 1,500 jets and the partners procured none, according to the report.

The U.K. National Audit Office (NAO) released a report on May 10, 2013, that said the F-35B could not land vertically on a carrier deck in "hot, humid and low pressure weather conditions without having to jettison heavy loads." The defense ministry said it was aware of the issue and was developing a solution that would be ready by 2020.

The report also supported the government's decision to buy the F-35B, instead of the F-35C as determined under the 2010 Strategic Defense and Security Review. The 2010 decision was based on flawed assumptions and immature data. Information on overall affordability, cost of conversion for the QUEEN ELIZABETH -class carriers and the degree to which French and U.S. jets could cross-deck with the British ships were all inaccurate, according to the report. The NAO said the F-35B option without the proposed electromagnetic aircraft launching system (EMALS) would be 1.2 billion pounds (US$1.9 billion) cheaper over 10 years than the F-35C option. The figure was halved to 600 million pounds (US$934 million) over 30 years due to the higher procurement and support costs associated with the F-35B. The U.K. estimated that supporting the F-35B would cost about 20 percent more than the carrier variant.

Aviation Week & Space Technology reported on May 29, 2013, that the Navy had identified several flight modifications required by landing helicopter dock ships operating F-35B aircraft. The changes were needed to "offset the increased stresses associated with JSF exhaust. The exhaust patterns and flight characteristics of the F-35 required the shielding, relocation and removal of vulnerable systems that could sustain damage during flight operations, such as antennas, life rafts, life rails, safety nets and JP-5 fuel stations," said Navy officials.

"The unique heat signature of the F-35 has required reinforcement of the flight deck to alleviate stresses from the heat of the jet, as well as modifying the flight deck coating to reduce erosion caused by jet exhaust associated with increased thrust. Specific system modifications that are unique to F-35 will also require the installation of new voltage regulators and rectifiers. Expanded mission capabilities of the F-35 have also required enhanced munitions throughput and systems capabilities to facilitate increased ordnance delivery and aircraft associated support equipment," according to the Navy.

Some of the modifications included relocating or shielding the Phalanx close-in weapon system and Rolling Airframe Missile and Sea Sparrow missile launchers and protecting fuel stations. The WSC-8 satellite communications antenna would be moved. Aqueous film-forming foam systems were being expanded. The Navy did not indicate how long the modifications would take.

Aviation Week & Space Technology on July 1, 2013, reported that the latest schedule for the F-35 was at risk. Software needed to meet the Marine Corps limited initial operational capability date was already expected to be eight months late relative to the August 2011 integrated master schedule, according to Michael Gilmore, the director of operational test and evaluation. Radar and electro-optical system issues had delayed weapons integration. Buffet and transonic wing drop "continue to be a concern to achieving operational combat capability," he told the Senate Defense Appropriations subcommittee.

Much of the software delays were attributed to the need to add tests at a rate that more than offset better-than-scheduled testing performance. The main causes were the helmet-mounted display system and regression testing. The latter ensured changes do not cause problems in areas previously evaluated. Regression testing had forced the addition of 366 test points in 2013, according to Gilmore.

Flight testing of Block 2A software, the last non-combat release, was only 35 percent complete at the end of May 2013. Trials began in March 2012 with the goal of concluding in February 2013. The Block 2B release, which was the standard the Marines planned to have for their initial operational capability, had been scheduled for delivery for flight-testing in August 2013, but was not expected before April 2014, said Gilmore.

The Block 3I software, which would serve as the basis for the Air Force's planned initial operational capability in late 2016, was also under a tight schedule. The software was connected to significant changes to the radar and electronic warfare and communications-navigation-identification processors. Lot 6 F-35s, which would begin arriving in 2014, included this new hardware and could not fly without the Block 3I software. One challenge was that the program must deliver an operational Block 3I release while also developing the Block 3F software, which was designed to meet the key performance parameters set in 2001. Lockheed Martin at the time said that prime software design for the Block 3F release was 41 percent complete.

Software fixes to reduce the effects of jitter on the helmet-mounted display were successful, but introduced another instability, which was described as "swimming" of the symbology. The light-leakage fix required the pilot to adjust the display brightness as the ambient light changed, said Gilmore.

Weapons integration was described as "very slow." Synthetic aperture radar modes provided inaccurate coordinates, while the electro-optical targeting system had difficulty maintaining tracks. Such problems had to be fixed before weapons tests could begin. However, schedule margin for Block 2B and Block 3F weapons testing was used up before any trials were performed. The last Block 3F weapon-integration tests were expected to be completed in late 2017 instead of fall 2016, according to Gilmore, making starting operational testing of Block 3F in January 2018 a challenge.

Buffet and transonic roll-off -- wing drop in high-speed turns associated with the asymmetrical movements of shock waves -- still affected all three F-35 variants despite control law changes. More testing was expected to assess the problem, but the limit of what could be achieved by control laws had been reached, said Gilmore. Further changes would degrade maneuverability or overload the structure.

The F-35 Joint Program Office announced on Oct. 10, 2013, that it had decided to stop development of an alternate helmet. Work would focus on bringing the Rockwell Collins/Elbit Systems Vision Systems Generation 2 helmet then being used for testing and training up to the fully compliant Generation 3 standard. A cost guarantee by the industry team resulted in a 12 percent reduction in cost for the helmet system. Selecting the VSI helmet would also avoid the US$45 million needed to complete development of the alternative BAE Systems helmet. Improvements to the Gen 2 helmet were being incorporated into the production line. These would meet the requirements for the July 2015 planned initial operational capability date for the Marine Corps, reported Flight International. The Gen 3 helmet would be introduced as part of low-rate initial production Lot 7 in 2016, according to the program office. The Gen 3 helmet features an improved night-vision camera, new liquid-crystal displays, automated alignment and software improvements.

Flight International for Oct. 15, 2013, reported that the U.S. Defense Contract Management Agency (DCMA) had imposed a 5 percent penalty against Pratt & Whitney for future billings on the F135 engine. The measure, imposed on Sept. 30, 2013, affected work under low-rate production Lots 5 to 8 as well as a U.S. Navy contract to reduce fuel burn on the engine. The penalty came after Pratt & Whitney was found non-compliant with its earned value management system.

Reuters reported on Oct. 10, 2013, that two minor cracks had been discovered in one of the four primary wing carry-through bulkheads of an F-35B aircraft. The cracks were found during durability testing in late August and took place after about 9,400 hours, which is the equivalent of about 17 years of operational flying, according the Pentagon. The discovery would not affect current F-35B flying operations, said Lockheed officials. The issue could be fixed with a design change that would add less than 2 lb (0.9 kg) to the aircraft's weight. The modifications would begin to be incorporated with the LRIP Lot 8 F-35Bs. The cracks were less severe than a similar bulkhead problem uncovered in 2010. The F-35B cracks did not affect the F-35A or F-35C models, program officials said. About 50 F-35Bs would require bulkhead repairs.

On Dec. 23, 2013, an F135 engine experienced a fan failure during accelerated mission tests on a ground engine at Pratt & Whitney's facility in West Palm Beach, Fla. The engine involved was the F135 engine with the highest service time in the test fleet, with 2,200 hours of running time, or about nine years of service. The engine had more than four times the hours of any engine used in F-35 flight testing and more than 10 times the hours of any operational F135 engine, according to Pratt & Whitney. The failure occurred in the front state of the F135's three-stage fan with the engine operating in conventional mode. The cold section of the engine suffered damage, while the hot section and lift fan were unharmed, according to Lt. Gen. Christopher Bogdan, the F-35 program manager. The stages were made up of integrally bladed rotors (IBR), the first of which was made from hollow titanium. The second and third stages were constructed from solid titanium. Manufacturing and cost issues with the hollow IBRs had already prompted Pratt & Whitney to redesign the fan. Lessons learned from the failure would be incorporated into the redesign, which involved producing the first-stage IBRs from solid titanium. The redesign was expected to add about 6 lb (2.7 kg) to the total weight of the engine, but simplify manufacturing. The IBR was previously changed to a hollow unit as part of weight-reduction efforts.

2015

Flight International for Jan. 13, 2015, reported that the F-35 program office insisted that the 25-mm cannon and electro-optical targeting system (EOTS) would be available and meet requirements by 2017. The office acknowledged a development issue for the GAU-22/A and some operational limitations on the EOTS. The program office said the cannon capability would be delivered with the Block 3F software, which was scheduled to become operational in fiscal 2017 with aircraft in low-rate production Lot 9. Lab testing in December 2014 had identified a minor issue with the software controlling the gun system, which was due to be fixed in early 2015. As for the EOTS, it would enter service with the ability to transmit still images to the ground via the Link 16 data link. The system would initially lack several common features on targeting pods, such as higher definition video; longer range target detection and identification; and an infrared marker and pointer. Those capabilities would be made available in later block upgrades, according to the program office.

On Jan. 16, 2015, Bloomberg News reported that flawed software would inhibit the initial F-35 jets that were to be declared operational, limiting the aircraft's ability to deploy ordnance, share data and track enemy radar. "Serious deficiencies with hardware and software used to develop data files" in the plane's computers are "more numerous and serious" than those first identified in 2012, according to Michael Gilmore, the Pentagon's director of operational testing and evaluation (DOT&E). The files are needed to identify enemy radar and are vital for effective combat operations against advanced hostile air defenses. Deficiencies in the Block 2B software also included "fusion, radar, passive sensors, identification friend-or-foe" and electro-optical targeting. The software did show some improvement in starting the aircraft and maintaining in-flight stability, according to the report.

Positives identified in the program included improved reliability of 7.5 hours between critical failures, up from three hours in 2013. The objective was 12 hours. Problems with the auxiliary air inlet door; propulsion system drive shaft and clutch; and a "roll post nozzle" actuator also appeared to be fixed, the report found.

Unresolved issues included an increase of 82 lb (37 kg) in the aircraft's empty weight since August 2011, bringing it within 1 percent, or 337 lb (153 kg), of its weight limit. The Distributed Aperture System continued "to exhibit high false-alarm rates and false target tracks, and poor stability performance, even in later versions of software." Current versions of the automated logistics system, which schedules aircraft maintenance, monitors in-flight aircraft condition and brings together spare parts remained behind schedule and had problems that render it "cumbersome to use and inefficient."

Aviation Week & Space Technology reported on Jan. 20, 2015, that the operational utility evaluation for the Block 2B software for the F-35 had been removed from the schedule in April 2014 at the recommendation of the director of operational testing and evaluation. Driving the move was the time needed to bring sufficient aircraft to a representative Block 2B configuration to support the trials. This would have delayed the start of the evaluation until late 2016, potentially delaying the development of the Block 3F software. Instead of the full trials, "limited assessments" of Block 2B capability would be conducted using F-35A operational test aircraft, according to the fiscal 2014 DOT&E report. Developmental testing of the Block 2B software was scheduled to be completed in February 2015. As of mid-2014, the Block 2B software still contained 151 mission-critical deficiencies, some of which might not be corrected until the final Block 3F software was finished.

The report also identified a major risk to the Marine Corps goal to declare initial operational capability for 2015. This was the availability of "mission data load" software, which works with software permanently loaded in the aircraft and contains information to operate sensors. The first two mission data loads were not expected to be available until November 2015.

Flight International for Jan. 27, 2015, reported that "slower than planned progress in mission systems, weapons integration and F-35B flight sciences testing" had delayed the conclusion of testing for Block 2B software fleet release, according to the DOT&E report. Trials were projected to be completed by the end of January 2015. At the time, the program office said that about 60 percent of the overall test program was complete. While more test flights were accomplished in 2015 than planned, the completion of test points for software Blocks 3B and 3I lagged. Deficiencies in the aircraft's navigation system also prevented the completion of all of the weapons delivery accuracy tests planned for 2014. The report also found "overall suitability" of all three F-35 variants to fall short and that reliability and maintainability for fielded jets still relied heavily on contractor support and "unacceptable workarounds." The program office said that availability for the jets was at 50 percent or better since October 2014. The first 10 Marine Corps F-35Bs required to declare initial operational capability had been fully cleared to release weapons, with the relevant part of the Block 2B software having completed testing.

Inside Defense reported on Feb. 25, 2015, that the internal weapons bay of the F-35B could not accommodate the required load of Small Diameter Bomb IIs (SDB IIs). A hydraulic line and structural bracket would need to be redesigned and modified ahead of the Block 4 release in fiscal 2022, according to the program office. As currently configured, the F-35B could only fit four of the eight required SDB IIs. Program officials said they had been aware of the issue for some time and that a contract was likely to be awarded to Lockheed for the design changes later in 2015. Redesign work was expected to be completed in 2016. The goal was to have the modifications implemented in post-systems development and demonstration aircraft delivered starting in 2019.

On March 11, 2015, Breaking Defense reported that the Air Force was still building the threat library for the F-35 and that much of the combination of the F-35's fusion software and threat information would not be ready until close to the Air Force's initial operational capability date. Full integration of threats and aircraft software was not expected until close to full operational capability, in part because of the time needed for pilots, intelligence analysts and the manufacturer to determine what the sensors were capable of and how the software could be modified to optimally combine sensor and threat data.

The Wall Street Journal reported on March 24, 2015, that Lockheed Martin would likely lose part of a US$300 million incentive fee due to software issues in the first 10 F-35Bs to be delivered to the U.S. Marine Corps in the summer of 2015. Those initial aircraft would come with software and other short-term fixes, which wouldn't affect combat readiness, according to Lt. Gen. Chris Bogdan, the program manager. Marine officials said that they still expected the F-35B to be ready for operational service that summer. Bogdan said a number of problems remained to be resolved. These included issues with the autonomous maintenance system; finalizing training; and fixing long-standing issues with the tires. The fourth version of the tires was performing better than previous models, according to Bogdan. Even with the problems, the F-35B would be able to drop bombs and fire air-to-air weapons.

Extended testing of modified software to correct the deficiencies began flight trials in mid-March 2015, noted Bloomberg News on March 24, 2015. The deficiencies were discovered in the most complicated test flights, with four F-35s observing air and ground threats and passing that data to each other via data links and using their onboard computers to fuse the information and create a common picture. The software at times "creates an inaccurate picture for the pilot," the Air Force said.

Aviation Week & Space Technology reported on April 6, 2015, that Pratt & Whitney expected to complete modifying F135 engines for the entire F-35 fleet by the first quarter of 2016. A long-term solution to the problem that caused a catastrophic engine fire on an F-35A in 2014 was also expected to be defined by the middle of the summer of 2015. The interim fix deepened the gap in the polyimide foam lining between the tips of the stators and the knife-edge seal forward of the third-stage integrally bladed rotor. The gap enabled the spinning seal to pass through the end of the stators without creating friction. Possible long-term solutions being evaluated included adding a hard coating to the seal plate to resist microcracks caused by the frictional heating or a combination of treating and a coating. The pre-trenching had a minimal effect on engine performance, company officials said.

Flight International for April 21, 2015, reported that the Dept. of Defense was reconsidering its maintenance strategy for the F-35 after dealing with problems with the ALIS. The system was designed to receive information from an aircraft during and after each flight, then automatically detect and troubleshoot all systems and parts failures and generate orders for spare or replacement parts. However, the system's 5 million lines of software code contained many bugs and maintainers said it had a false positive rate of about 80 percent. The ALIS also proved too bulky to deploy aboard USS WASP during at-sea testing of the F-35B. A lightweight version would be ready in time for the Marine Corps declaration of initial operational capability in mid-2015, according to the program manager. Pentagon officials were also rethinking the "just-in-time" logistics model.

On April 27, 2015, Bloomberg News reported that the Government Accountability Office had found that the F-35 engines were proving so unreliable that increased production of the jet might be slowed. Data from flight tests evaluated by the GAO found that the reliability of the F135 engine was about half what it should be and had limited the progress of the program. The GAO cited the need to make design changes to the engines and then retrofit them to aircraft that were already built along with software flaws. The report also warned that the Pentagon's procurement plan might not be affordable.

As of late December 2014, the engines on the F-35B flew about 47 hours between failures caused by engine design issues instead of the 90 hours planned at this point, the GAO said. The F-35A and F-35C engines flew about 25 hours between failures instead of the planned 120 hours.

A spokesman for Pratt & Whitney said that the GAO had "incorrectly assessed engine reliability, as it did not account for new designs that have been validated and are being incorporated." The F-35B was at 71 percent of where it was expected to be and had consistently improved since 2013, the spokesman said. The F-35A's engine was at 147 percent where it was expected at that point. The GAO had "confused engine spec reliability and aircraft spec reliability, which are measured differently," the spokesman said. The Pentagon had already validated the engine's reliability performance.

Pratt & Whitney officials told National Defense magazine that the current configuration of the F135 was on track for full maturity by 2020. Engines then under construction would have all the fixes identified so far, while those engines on operational aircraft would be retrofitted. The engine program would be considered mature when it exceeded 200,000 flight hours, or each of the three variant engines had more than 50,000 flight hours.

Flight International reported on June 8, 2015, that an accident investigation board had finalized the cost of the catastrophic engine failure at US$50 million. The panel confirmed that the fire was caused by the failure of the third-stage rotor of the engine fan module.

DoDBuzz reported on June 15, 2015, that Pratt & Whitney planned to complete retrofitting the F-35 fleet with an engine fix developed after the 2014 engine failure by early 2016. At the time, Pratt & Whitney had delivered nearly 230 F135 engines to the Pentagon, company officials said. Of the nearly 130 flying, more than 50 had been retrofitted with the fix. The modification had been integrated with the production cycle, so that all new engines contained the fix, the officials said.

In a report dated June 22, 2015, Frank Kendall, the undersecretary of defense for acquisition, said that all but eight of the 243 software capabilities needed for initial operational capability were set to be completed and verified before the Marine Corps declared the milestone for the F-35B. The unresolved issues included software used to fuse data from air and ground sensors; electronic warfare; and air-to-air and air-to-ground data links. The issues were expected to be resolved during the testing of more capable software in late 2017, reported Bloomberg News.

In a memo dated July 22, 2015, Michael Gilmore, the director of operational testing for the Pentagon, said that a 12-day at-sea exercise with the F-35B aboard the USS WASP demonstrated problems with shipboard reliability and maintenance. During the trials, "Marine maintainers had rapid, ready access to spare parts from shore" and "received significant assistance" from Lockheed and subcontractor personnel. Despite this support, "aircraft reliability was poor enough that it was difficult for the Marines to keep more than two or three of the six embarked jets in a flyable status on any given day," Gilmore said. A Marine Corps spokesman said the service did not agree with all of the conclusions and opinions in the report, which contained statements that lacked proper context or qualifying information, reported Bloomberg News. The spokesman also said the F-35B had a readiness rate of 65 percent during the exercise. Four of the aircraft assigned to the Marine Corps' first operational squadron participated in the exercise. One experienced "multiple maintenance issues" that prevented it from flying for four days, the report said. Problems with fuel systems, including two major component failures, also hindered the training.

Combat Aircraft for September 2015 evaluated reports that an early F-35A test aircraft flying clean had been comprehensively out-maneuvered by a two-seat F-16D carrying a pair of 230-gal underwing fuel tanks. The full report detailing the flight, which was seen by the magazine, indicated that it had included an offensive capture, tracking tasks and a number of traditional basic fighter maneuvers. In all, there were 17 engagements between the two aircraft. The report said that the most noticeable characteristic of the F-35A in a visual engagement was its "lack of energy maneuverability," which it described as being inferior to the F-15E due to having a "smaller wing, similar weight and 15,000 lb less in afterburner thrust."

"Even with the limited F-16 target configuration, the F-35A remained at a distinct energy disadvantage for every engagement," the report said. The Lightning II was also said to have an "insufficient pitch rate," which prevented the jet from pulling "lead" on the target offensively and made it hard to defeat enemy attacks. No effective guns defense was found during the test.

The report said that at high angles of attack (AoA), the F-35A could generate very high yaw rates, which provided limited opportunities for missile shots, but at the cost of losing energy. The test pilot assessed that "deciding to commit to high AoA meant losing the fight unless the bandit made an error." The fighter's flying qualities were also found to be neither intuitive nor favorable in the "blended region." The F-35's performance was sufficiently poor that the test pilot said it would be "inappropriate" to fight other aircraft within visual range.

The magazine said that the test was intended "to test the flying qualities of the F-35 using visual combat maneuvers to stress the system." It was designed to allow the F-35 to maneuver to the edge of its limits, while handling in a positive and predictable manner. The F-16D involved in the test flight was used as a visual reference to maneuver against. The goal was to gather data and not to win the fight.

Combat Aircraft noted that fifth-generation jets, such as the F-22 and F-35, might not be best considered as fighters in the traditional sense, because they are "sensor-shooters" that can perform a variety of roles, from fighter, bomber, attack, reconnaissance, signals intelligence, electronic attack and command-and-control in a range of threat environments. Experts have noted that a single F-35 can create "effects" that would previously have required numerous aircraft.

The F-35 will provide close air support and fighter capabilities differently than its predecessors due to new capabilities, sensors, weapons, tactics and doctrine, the magazine said. As a result, potential areas of performance weakness compared to earlier aircraft may not be that significant.

The secretary of the Air Force on Oct. 16, 2015, announced that the service had recently decided to restrict pilots weighing less than 136 lb (62 kg) from flying the F-35A due to safety concerns about the ejection seat in part of the flight envelope. A recent test of the escape system identified an unacceptable risk of neck injury during parachute deployment/opening for lighter pilots at low speeds. The requirement was for the seat to be certified for any pilot weighing between 103 lb (47 kg) and 245 lb (111 kg). An unacceptable risk was found for pilots weighing less than 136 lb, said the release from the Air Force secretary. Only one pilot was affected by the decision. He was transferred to the F-22 fighter program, officials said. There was also an elevated level of risk for pilots between 136 lb and 165 lb (75 kg). Such pilots were permitted to continue flying in part because of the low probability of an event requiring ejection. The restrictions were expected to be lifted once the issue was resolved.

During an ejection from the F-35, the canopy is shattered by an explosive charge. The entire seat is then propelled upward with significant force. Mannequin tests over the summer of 2015 demonstrated that the lightest F-35 pilots would be rotated backward into a position where they would likely be killed by the rocketing parachute's force snapping their heads, reported Congressional Roll Call(Washington, D.C.). The only mannequins suffering broken necks during the ejections were those wearing the latest, heaviest helmets, according to officials. There were three fixes in the works to reduce the risk of neck injury: installing a switch on the seat for lighter pilots that would slightly delay parachute deployment and reduce parachute opening forces; designing a lighter helmet; and mounting a head-support panel that would protect the pilot's head from moving backwards during parachute opening.

Reuters reported on Oct. 21, 2015, that F-35 program officials said that it could take another year to resolve the ejection seat issues.

Defense News reported on Jan. 9, 2016, that the Air Force would not lift weight restrictions on F-35 pilots until 2018 at the earliest. More testing was needed to address safety issues with the ejection seat, said an Air Force spokesman. Three fixes were expected to be ready for implementation by early 2018. The delay was due in part to increased testing needed for the head support panel and connecting it with the lightweight switch, said the service spokesman.

On Dec. 11, 2015, Michael Gilmore, the director of operational testing at the Pentagon, sent a memorandum to Frank Kendall, undersecretary of defense for acquisition, technology and logistics, and Gen. Paul Selva, vice chair of the Joint Chiefs of Staff, warning that the Block 3F software would not be ready on schedule by July 31, 2017. The Block 3F software is the culmination of the system development and demonstration phase and meets the requirements set at the start of the program, noted Aviation Week & Space Technology on Jan. 22, 2016. Gilmore warned that the program was risking further problems by attempting to define the Block 4 software in early 2016, when Block 3F and Block 3I were still "problematic" and performing poorly in testing. The program office had yet to order vital equipment for software labs needed to support operational testing and initial operational capability, said Gilmore. The program office acknowledged removing tests from the program and that each software block, including Block 3F, would enter service with deficiencies. The Block 3F issues would have to be remedied as part of Block 4. Customers would have to decide whether all the shortcomings would need to be fixed and when, said the program office.

Block 4, the first post-service-entry upgrade, was too aggressive and under-resourced, according to the memo as cited by the magazine. Many of the issues were the result of "schedule-driven decisions" made during the re-baselining of the program from 2010 to 2012. The program office said that it recognized about "four months of potential risk" in the Block 3F schedule. Gilmore said that Block 3F software was buggy and expected to get worse. The schedule did not account for this. The program office argued that there would be sufficient opportunity to correct deficiencies from Block 3F in the early stages of Block 4. Safety-critical deficiencies would have the priority.

The root of the problem was an incremental software process. For example, the Block 2B software, used only on a single squadron of Marine F-35Bs, was fielded with hundreds of operational deficiencies. Block 3I was created by re-hosting the 2B capabilities on new processers, resulting in "avionics instabilities and other new problems [and] poor performance during developmental testing." Finally, the program office decided to develop Block 3F by adding capabilities incrementally to the deficient Block 3I software.

Gilmore said that the mission data reprograming lab, which produces mission data file software that allows F-35 sensors and processors to identify and display threats and targets, did not have the required equipment to adequately develop and test mission data loads to support the Air Force's initial operational capability configuration (Block 3i) or initial operational testing of Block 3F.

The letter also said that the ALIS "continues to struggle in development with ... a complex architecture with likely (but largely untested) cyber deficiencies," reported Jane's Defence Weekly. The F-35 Joint Program Office also acknowledged the need for more robust cybersecurity testing.

2017

Business Insider reported on Jan. 4, 2017, that the Pentagon had set up a "red team" to address numerous shortcomings with the F-35C carrier-based fighter. The Navy variant suffered from an issue with its nose gear during catapult takeoffs and landings from aircraft carriers. The problem, detailed in a service report with data going back to 2014, involved rough takeoffs that hurt and disoriented pilots as they were taking off from the carrier. The problem was caused by several design factors and the red team recommended fixes that would take from several months to several years to fix. Long-term actions to address the issues would not occur until 2019 and the work would last 12 to 36 months, according to the report. Aircraft and carrier redesigns might be necessary to fully address the problem. A Pentagon report in 2015 noted that extreme movements in the cockpit during launch risked pilot health. In December 2016, Lt. Gen. Christopher Bogdan, the program manager, said that the F-35C takeoff problems only occur when the jets take off with low weight loadouts. The problem was not present when the aircraft was more laden with ordnance or fuel, he said.

Delayed delivery of vital software and shortfalls with ALIS was expected to push back the start of initial operational test and evaluation (IOT&E) by at least a year from its planned August 2017 date, reported Flight International for Jan. 24, 2017. Michael Gilmore, the outgoing director of operational test and evaluation, said that early 2019 was an optimistic date for the start of IOT&E in a final report. The document also warned that hundreds of deficiencies would push full combat testing to late 2018 or early 2019. Flight sciences testing identified issues that would postpone IOT&E, including excessive and violent oscillations experienced by the F-35C during catapult launches. The Navy considered it a "must-fix" issue and directed that it should be addressed before the final testing phase began. The fiscal 2016 report for the operational testing office said that 270 high-priority deficiencies had been identified in the Block 3F software during a recent review and that Lot 10 production models would be delivered without full combat capability, including 9 g maneuverability and support for gun testing. Also behind schedule was Small Diameter Bomb integration, the addition of Link 16 and multifunction advanced data link systems. The ALIS 3.0 system would not be delivered until mid-2018 and several capabilities would be further delayed until later in that year. Mission data loads, which help identify friendly and hostile radar signals for specific geographic regions, would not be verified until 2019 at the earliest, said the report. Once delivered, these would not be ready to face threats in testing, much less combat, said the testing office. Gilmore emphasized that the deficiencies would increase costs and that the program office must look within its existing budget or at funding planned for follow-on modernization to cover any overruns.

Defense News reported on Feb. 13, 2017, that the Air Force could remove restrictions on lightweight F-35 pilots as soon as April 2017, as a result of fixes to the jet's ejection seat and helmet. Even if the modified Martin-Baker US16E ejection seat meets requirements, the Air Force could still go ahead with certifying a second ejection seat in case of future issues, said Brig. Gen. Scott Pleus, the head of the F-35 integration office. At the time, testing of the modified escape system was mostly complete. Once approved, it would likely take a few months to implement retrofits for the seats. At that point, the service would be able to begin training lightweight student pilots, said Pleus.

Martin-Baker and Rockwell Collins, the helmet maker, had made three major changes in order to make the escape system safe for lightweight pilots, the newspaper said. A new switch in the US16E ejection seat alters the parachute loads to accommodate pilots of different weights. A head support panel helps protect the head and neck from stress upon ejection. The weight of the Rockwell Collins helmet was cut from 5.1 lb (2.3 kg) to 4.6 lb (2.1 kg). It was expected to take about two years to refit all of the service's F-35s.

Flight International for Feb. 14, 2017, reported that Lockheed Martin had warned that the F-35 program would miss its US$85 million unit cost goal in three years unless the Pentagon implemented another affordability program. The cost target, including the F135 engine, would be impossible to meet without cost reductions in the manufacturing system, a block buy deal or an increase in order quantity, company officials said.

Defense News reported on March 13, 2017, that the current configuration of the F-35A was unable to hit a moving target, unless a human was manually directing the bomb. The Air Force planned to change this over the following year by integrating the GBU-49 Enhanced Paveway II. The weapon was not originally included in the Block 3F weapons loadout, which along with new software would make the F-35 fully mission-capable. The service decided to add the capability over the previous six to nine months, Air Force officials said. The ability hit a moving target is a major capability for close-air support operations and the GBU-49 meets that requirement, said the officials. GBU-49 integration work was expected to be completed by the end of 2017.

The F-35 electro-optical targeting system (EOTS) can find a moving target, lock onto it and track it, but the pilot must still predict where a target will move and aim there. The GBU-49 has lead-laser guidance, which calculates how far a weapon should travel beyond the target's current location to hit it, needing only a laser spot on the moving target, according to Air Force officials. The weapon's proportional navigation software automatically calculates and compensates for target direction speed and its inertial measurement unit adjusts for wind conditions, noted Aviation Week & Space Technology for March 6, 2017. A lead-laser guidance capability for the F-35's EOTS was scheduled for Block 4.2, which was scheduled for delivery in 2022.

On March 22, 2017, Defense News reported that Lockheed expected to soon receive a preliminary report on a potential fix for a nose gear problem on the F-35C. Live carrier trials of the fix were anticipated in the fall of 2017. Testing aboard the carrier USS GEORGE WASHINGTON in 2016 demonstrated that the F-35C would bob up and down on its nose gear when being launched from a catapult. The issue prevented pilots from reading instruments while trying to take off. A number of pilots also said that the motion caused pain.

Testing of two potential fixes had just concluded at Joint Base McGuire-Dix-Lakehurst. The first involved changing how pilots strap into the jet, including "how they get into the seat, how they pull their harnesses and make sure they are in proper position," said Jeff Babione, the Lockheed program manager. The second evaluated having "just a little bit less load holding the airplane back when it launches off the catapult" to reduce the stored energy in the nose gear, he said.

Flight Global reported on April 3, 2017, that the Air Force had still not determined how to fix the communication gap between the F-35 and F-22 . At the time, the F-22 's Link 16 network could only receive data from the F-35. The F-35 could transmit and receive data with other Link 16-equipped aircraft, including the F-16 , F-15 and other NATO aircraft. The F-35 would not be able to receive F-22 data until a fourth- to fifth-generation gateway was deployed. There was not yet a program of record for fourth to fifth-generation communications that would cover the F-22 's Link 16, officials said.

The F-22 uses an intra-flight data link (IFDL) to communicate with other Raptors, while the F-35 uses the Link 16 and Multi-Function Advanced Data Link (MADL), said program officials. Both IFDL and MADL have a low-probability of intercept and low-probability of detection capability that deters jamming and eavesdropping. But the two systems cannot talk to each other, officials said.

The GAO issued a report on April 24, 2017, that warned that development testing for the F-35 could be delayed by 12 months at a cost of an additional US$1.7 billion. In an update for Congress, the watchdog said that the Joint Program Office had adopted an "optimistic" estimate for a five-month delay and US$532 million cost overrun to complete the Block 3F software configuration, reported Flight International for May 2, 2017. The GAO's analysis indicated that Block 3F testing would not conclude until May 2018, a year later than scheduled at the time. The anticipated cost growth would increase the total price tag to US$56.8 billion, around US$22.4 billion more than originally estimated in October 2001. Such a delay could force the Navy to postpone its declaration of initial operational capability for the F-35C, which was planned for fiscal 2019. It could also affect the launch of a Block 4 software modernization project slated for fiscal 2018 and program office plans to buy the aircraft in economic order quantities rather than annual procurement lots, the agency said.

Bloomberg News reported on April 25, 2017, that the Defense Contract Management Agency projected that Lockheed would deliver 57 F-35s in 2017, nine fewer than planned. The company "did not meet contract requirements in 2014, 2015 or 2016," the agency noted. However, Lockheed's performance had improved from the 2014 to 2016 timeframe. Company officials said that the 66-jet goal would be reached unless "we have some big problem." At the time, Lockheed had delivered 17 F-35s, three ahead of schedule, according to a Lockheed spokesman. Nine more aircraft were nearing delivery. The 66 planned aircraft included 37 originally anticipated and 29 that ran late from previous contracts, according to the program office.

The Air Force News Service reported on May 15, 2017, that service leaders had recently removed restrictions that prevented lightweight pilots from flying the F-35A. The restrictions were imposed in 2015 because of concerns about the risk during ejections in part of the flight envelope. After testing, three modifications were implemented: a switch on the seat that slightly delays parachute deployment at high speeds and decreases parachute opening forces for lightweight pilots; a head support panel on the rear risers of the parachute to prevent the pilot's head from moving backward during an ejection; and overall helmet weight was reduced through the reduction of internal strapping material and the removal of an additional external visor, which decreases injury risk during parachute opening. The new ejection seats were being retrofitted into 100 F-35As already delivered, while the lightweight helmets were in pre-production. Full production was to begin later in 2017. No pilots under 136 lb (62 kg) had moved through the F-35 training pipeline since 2015, when testing showed unacceptable risk of head or neck injury for lightweight pilots, noted Defense News. The Air Force expected to begin training its first lightweight student by the end of 2017.

The Air Force grounded all F-35s at Luke AFB on June 9, 2017, after pilots complained of hypoxia-related issues, reported Military.com. A total of 48 aircraft and 49 pilots were affected by the order, said a service spokeswoman. Since May 2, five pilots reported physiological incidents while flying, she said. In each case, the aircraft's backup oxygen system activated and the pilot landed safely. Training flights were scheduled to resume on June 12, 2017, after a day of safety briefings, reported the Las Vegas Review-Journal. F-35 operations ultimately resumed on June 21 after several protective measures were implemented. Brig. Gen. Brook Leonard, the commander of the 56th Fighter Wing, lifted an altitude restriction on F-35 flights at Luke AFB on Aug. 30, 2017. The aircraft had been restricted to flying at altitudes below 25,000 ft. A specific cause of the hypoxia-related issues had not yet been found, but the service had reduced possible causes for labored breathing and carbon monoxide ingestion and refined procedures and training, the general said in a statement cited by Defense News. There had only been one additional incident of hypoxia-like symptoms in the two months since the grounding, noted officials.

Bloomberg News reported on June 28, 2017, that the F-35 and its parts were not as reliable as expected and it was taking longer than anticipated to make repairs. About 20 percent of the aircraft were awaiting spares in depots because suppliers could not keep up with expanding production while fixing returned parts, said a presentation by the Pentagon's director for operational testing acquired by the news service. Costs to operate and support the F-35 would grow if the reliability issues were not fixed, the report said. The availability of spare parts for the 203 F-35s already assigned to bases "is getting worse, affecting fly rates" and pilot training, said the presentation, which was dated May 8, 2017. Reliability metrics connected to "critical failures have worsened over the last year" and improvement "has stagnated," said the study. These trends likely meant that the long-term lifecycle costs of the F-35 would increase significantly over the US$1.2 trillion estimate. A spokesman for the F-35 program office said that since 2015, the office's estimate of annual operating expenses, including flying-hour costs, had fallen 2.2 percent for the F-35A; 3.3 percent for the F-35B; and 4.2 percent for the F-35C. This was the result of "improved maintainability and sustainability as the weapon system matures, the design stabilizes and maintenance" becomes more efficient and effective, the spokesman said. The testing office said that fleetwide availability of the F-35 was 52 percent, short of an interim goal of 60 percent and the 80 percent needed to start combat testing in 2018, said Bloomberg. The 52 percent figure was a combination of new and older aircraft, said the program office spokesman. Newer aircraft are showing "significantly better reliability and aircraft availability rates, he said. For example, the 388th Fighter Wing at Hill AFB currently indicated an availability of 73 percent.

On July 18, 2017, Defense News reported that the F-35 program office intended to make changes to the jet's onboard oxygen generation system to optimize the flow of oxygen to the pilot. The modification involved refining the algorithm associated with oxygen concentration, said a program spokeswoman. "There is no indication the delivered oxygen concentration was a contributor to any of the recent" hypoxia events, said the spokeswoman. The manufacturer of the oxygen system would be responsible for designing upgraded firmware as well as developing a path to retrofit all F-35 variants with the new capability, she said. The work was expected to take 24 months. There had only been one hypoxia incident at the time since flights resumed on June 21, noted an Air Force spokeswoman. That incident was blamed on an irregular oxygen valve that was replaced.

Bloomberg News reported on July 18, 2017, that the latest Pentagon special acquisition report on the F-35 said that Pratt & Whitney had been slow to incorporate promised cost-saving techniques for the latest and largest batch of F-35 engines. Under the latest contract, Pratt & Whitney was building 102 engines. The deal, signed in July 2016, was worth US$2.1 billion, including management, engineering support and spare parts. The F-35 program office estimated that there was about US$43 million in cumulative cost overruns for materials from July 2016 to April 2017. Pratt & Whitney would be responsible for those costs if they continued. Engine hardware was "costing more than planned" because the company targets weren't achievable "due to delays with incorporating enough engineering changes and affordability initiatives to lower the manufacturing costs," the report said. Pratt & Whitney had also "been unable to negotiate lower pricing from the supply chain," said the program office. As of April 2017, Pratt & Whitney was behind on US$51 million in work because of late engine hardware deliveries, some quality lapses with engine nozzle components and other supplier issues, said the report. A spokesman for the F-35 program office emphasized that the government was not paying for the additional costs. Despite the overruns, the engine cost targets were declining with each contract, the spokesman said.

The Marine Corps Times reported on July 21, 2017, that the night-vision camera on the helmet for the F-35B did not work when there was no moon, citing video of a test flight aboard USS AMERICA in November 2016. The F-35 Joint Program Office acknowledged the issue and said potential solutions were expected to be tested in the fall of 2017. During the test flight, the pilot was unable to see the deck of the AMERICA , forcing him to guess where he was above the ship, officials said. Several software changes were being made to "significantly improve the night-vision camera low-light level performance," a spokesman for the program office told Military.com.

Roll Call (Washington, D.C.) reported on Sept. 18, 2017, that problems remained with the F-35's ejection seat, despite an Air Force announcement in May that the problem had been addressed. On May 1, 2017, an internal report by the Technical Airworthiness Authority, the service's top aviation safety experts, said that 22 pilots would be injured or killed during the aircraft's service life unless the upgraded ejection seats underwent additional testing to demonstrate that they work in "off-nominal" situations, such as when the aircraft is out of control, according to the report, which was obtained by Roll Call. For about US$1 million worth of tests over nine to 12 months, the result could be "no additional losses" of pilots, said the report. The program office did not concur with the recommended testing, according to the safety authority. The Pentagon's directorate of operational testing agreed with the conclusion of the report. The program office "needs to conduct sufficient testing under off-nominal conditions to adequately characterize and assess the effect of off-nominal, (i.e., out-of-control) ejections," said a spokesman for the testing office. There were also concerns about the F-35 canopy, which is designed to lift and shatter before the ejection seat is released. The concern was that canopy fragments might hit the pilot during ejection, especially if the aircraft was out of control. A spokesman for the F-35 program office said that the ejection seats were not any riskier than others and that the potential dangers might occur only in rare instances. The more thorough testing was not cost-effective, the spokesman said.

On Oct. 23, 2017, Bloomberg News reported that maintenance facilities for the F-35 were six years behind schedule, citing a draft audit by the U.S. Government Accountability Office. The time to repair a part averaged 172 days -- "twice the program's objective" -- according to the GAO. The shortages were "degrading readiness" because the aircraft "were unable to fly about 22 percent of the time" from January through August 2017 due to a lack of parts. Operating and maintaining the aircraft was expected to become more challenging as the Pentagon accelerated production of the F-35. The Defense Dept. was already stretched "to meet the needs of continued system development and production" while also sustaining the more than 250 aircraft already fielded, said the GAO. The F-35 program office and Lockheed had identified steps to increase parts availability, the audit said, but Pentagon documentation indicated that "the program's ability to speed up this timeline is uncertain." The report also revealed that the F-35B would not have required maintenance and repair capabilities at sea and would "likely experience degraded readiness." The Marine Corps planned to begin ship deployments of the F-35B in 2018.

Repair capabilities for many components at six military depots were originally planned for completion by 2016, but some capabilities were delayed until 2022, the GAO said. This was in part because the Air Force and Navy were "not providing enough funding." However, service officials said the program office failed to "clearly identify some depot requirements in a timely manner." The Pentagon faced a US$1.5 billion funding shortage for fiscal 2018 to 2023 for F-35 sustainment "as well as significant readiness risks," the agency said.

The Daily Telegraph (London) reported on Nov. 21, 2017, that increasing costs might force the U.K. Ministry of Defense to reduce its planned buy of 138 F-35s. Officials told lawmakers that it was impossible to accurately project the cost of the program at the time. As costs became clearer, the ministry would adjust the program accordingly, the officials said. London had already signed a contract for an initial batch of 48 F-35s, which were estimated to cost 9.1 billion pounds (US$12 billion) by 2025, including training and maintenance. Once the jets were in service, the ministry would conduct an annual review of costs to help forecasts, said Lt. Gen. Stephen Poffley, the deputy chief of the defense staff. If later batches were delayed or costs increased, the ministry would have to adjust the number of aircraft ordered, officials said.

2019

Flight Global reported on April 2, 2019, that the Pentagon had halted the delivery of F-35 parts and manuals to Turkey after Ankara declined to cancel an order for the Russian S-400 air defense system. Washington was concerned that the system could expose vulnerabilities in the stealth jet, which could then be exploited by Russia. Until Turkey forgoes delivery of the S-400, the U.S. has halted deliveries and activities associated with Turkey's F-35 operational capability, said a Pentagon spokesman. If Ankara moves forward with the acquisition of the system, their ongoing participation in the F-35 program was at risk, the spokesman said. Removing Turkey from the program would disrupt the supply change. There are 10 different Turkish firms involved in the production of parts for every F-35. Defense Dept. officials said work had begun to identify secondary sources for replacement parts, reported Agence France-Presse.

The Government Accountability Office published a report on April 25, 2019, outlining how parts shortages were preventing the F-35 from flying as often as required. Aircraft performance was short of combat requirements largely due to a shortage of spare parts and difficulties in managing and moving components around the world, said the report, as cited by Breaking Defense. From May to November 2018, F-35s were unable to fly nearly 30 percent of the time due to the lack of parts. The Pentagon also had a repair backlog of about 4,300 F-35 parts. The GAO said that the system built by the F-35 program to supply U.S. and allies with parts was not effective enough. While the Defense Dept. procures some sets of F-35 components years ahead of time to support deployments, in some cases, these parts no longer fully match requirements due to modifications to the jets over time. For example, 44 percent of purchased parts were not compatible with Marine F-35Bs during a recent deployment, the report said. The backlog of parts awaiting repair was attributed to delays in setting up part repair capabilities at military depots. The GAO said the problem was unlikely to be resolved until 2024.

The GAO also found that only 2 percent of F-35Cs were fully mission capable during the six-month period; 16 percent of F-35Bs and 34 percent of F-35As met the mark, reported Defense News. The report said that the Pentagon only planned to buy enough parts to enable 80 percent of its F-35s to be mission-capable based on the availability of parts. This would likely only yield a 70 percent mission-capable rate at best, since it only accounts for jets on the flight line and not those in the depot for longer term maintenance. In addition, squadrons have cannibalized parts from aircraft unable to fly, hiding additional parts shortages, said the GAO.

ABC News (Australia) reported on May 6, 2019, that auditing firm KPMG had found that F-35As stationed at RAAF Williamtown were susceptible to "intergranular corrosion." The report called for the air force to consider around-the-clock dehumidification systems at the base to reduce the corrosion risk. Concerns about potential metal stress and cracking were initially raised in 2017. RAAF Williamtown, near Newcastle in New South Wales, was the only base identified as having possible problems due to salt and other climatic conditions. Intergranular corrosion can degrade metal, leading to stress cracking and tensile stress that can affect adjacent components. Aluminum Alloy 7085 used in the F-35 was said to have increased susceptibility to such corrosion, said KPMG.

On June 7, 2019, Foreign Policy reported that Acting Defense Secretary Patrick Shanahan had notified Turkish Defense Minister Hulusi Akar that Turkish pilots then in the U.S. for F-35 training would have to leave the country by July 31. Training for new F-35 students would also be halted. Should Turkey change its course on the acquisition of Russian S-400 air defense systems, then the training program could resume, said a senior U.S. defense official. If Turkey takes delivery of the S-400 before July 31, the "measured and deliberate" plan would be "nullified," according to a letter from Shanahan to Akar. Beginning on July 31, Turkish air force personnel would no longer be permitted to enter facilities belonging to the F-35 Joint Program Office and mandated that Turkey reassign its personnel from the office by that date. Work being performed by Turkish companies on the program would move to "alternative sources" as they were qualified, said the letter.

Defense News reported on June 12, 2019, that the F-35 continued to suffer from a range of deficiencies. According to documents obtained by the newspaper, the issues, if unresolved, could create risks to pilot safety and hinder its ability to complete its missions. The documents described 13 category 1 deficiencies, which are those flaws that affect safety or mission effectiveness. The outstanding problems could also affect the Pentagon's decision whether to advance the F-35 program into full-rate production later this year. The decision would significantly increase annual production from 91 in 2018 to nearly 160 by 2023. Typically, the Defense Dept. requires all deficiencies to be resolve before approving full-rate production.

The F-35 Joint Program Office was making progress, but not all of the issues would be fixed prior to the full-rate production decision, according to Vice Adm. Mat Winter, the program manager. None of the outstanding problems was due to the design, hardware or manufacturing processes, which would affect the production decision, he said. Nine of the 13 issues would likely be corrected or downgraded to category 2 before the Pentagon made its production decision. Two would be dealt with in future software builds, said Winter. Two issues would not be addressed, with the Defense Dept. electing to accept additional risk. The program manager emphasized that none of the flaws represented a serious or catastrophic risk to pilots, the mission or the F-35 airframe.

The program office told the newspaper that it had created two different designations of category 1 problems to highlight the difference between issues that would qualify as an emergency and others that are less significant. Category 1A problems represent threats to the pilot's safety or the potential loss of the aircraft. Those must be rapidly corrected, said Winter. Category 1B issues affect mission effectiveness with an existing workaround that is acceptable to operators with the deficiency to be fixed in the future.

According to one of the documents, at least 13 problems would remain in category 1 headed into operational testing in the fall of 2018. The identified shortcomings included:

• No way for the logistics system to allow foreign F-35 operators to keep their secret information from being sent to the U.S.
• The spare parts inventory shown by the logistics system does not always reflect its actual state, in some cases leading to mission cancellations.
• Cabin pressure spikes in the cockpit have been known to cause barotrauma, or extreme ear and sinus pain.
• In conditions at or below -30 degrees F (-34 degrees C), the F-35 will incorrectly report that one of its batteries has failed, in some cases leading to missions to be canceled.
• On the F-35B and F-35C, flight at speeds of Mach 1.2 or more can result in structural damage and blistering to the stealth coating.
• The F-35B and F-35C can lose some pitch, roll and yaw control after performing some maneuvers.
• If the F-35A or F-35B blows a tire on landing, the impact can damage hydraulic lines and pose a risk of catastrophic damage.
• A "green glow" sometimes appears on the helmet-mounted display, washing out helmet imagery and making it difficult for the F-35C to land on an aircraft carrier.
• On nights with minimal starlight, the night-vision camera sometimes displays green striations that make it hard for all variants to see the horizon or land on ships.
• The sea search mode of the F-35 radar only covers a small area of the ocean's surface.
• On very hot days, F-35Bs with older engines may not produce enough thrust during vertical landing, potentially leading to a hard landing.

Four additional category 1 deficiencies have been uncovered since December 2018, which mostly involved weapon interfaces, according to Winter. These would be resolved with software fixes, although they would likely not be addressed in time for the full-rate production decision, he said. More time would also be needed to fix the engine thrust issue and sea search mode on the radar. The structural and stealth coating issue on the F-35B and F-35C at speeds of more than Mach 1.2 would not be addressed, since it was assessed as having an extremely low probably of occurring during operations.

Winter also said the the program office was seeking to minimize the costs of fixing the issues, including bundling corrections with other software and hardware updates to minimize labor costs.

USNI News reported on July 17, 2019, that Turkey was being kicked out of the F-35 program after it began taking delivery of Russian-built S-400 air defense systems. The U.S. would pay around US$500 million to US$600 million to shift production of components from Turkey to the U.S., Pentagon officials said. Turkish firms built more than 900 parts for the F-35 and had been assigned more than US$1 billion in industrial participation, officials said. The process of removing Turkey from the supply chain would begin by March 2020. The process was not expected to have a large affect on the program, due to planning for the shift that had already been completed, noted Defense News.

On Aug. 1, 2019, Japan resumed flights of its F-35As, reported the Kyodo news agency. The return to flight status was approved following inspections of its remaining jets and additional pilot training. Defense Minister Takeshi Iwaya emphasized that Tokyo still planned to acquire a total of 105 F-35s.

Bloomberg News reported on Nov. 10, 2019, that a possible fix had been developed for the advanced helmet used by F-35 pilots. A problem with the helmet display caused a green glow when flying in very low light conditions. Lockheed Martin had been contracted by the F-35 program office to redesign the helmets and install new organic light-emitting diodes (OLEDs) in place of the traditional liquid-crystal displays. Company officials did not indicate how many helmets require modification or the upgrade cost. Other benefits of the OLEDs are the use of flexible screens, improved picture quality and quicker response. At the same time, such screens are noted for shorter lifetimes.

Air Force magazine reported on Nov. 13, 2019, that Lockheed Martin and Pratt & Whitney had mostly reassigned the production of some 850 F-35 components previously produced by Turkish firms to themselves and a few other American firms. About 20 percent of the work had been moved to overseas partners. A new source was still being sought for 11 aircraft components and an integrated rotor on the engine, said Lt. Gen. Eric Fick, the program manager. The final Turkish-built components would be delivered by March 2020, said Ellen Lord, the undersecretary of defense for acquisition and sustainment. The Turkish exit from the program was not expected to cause any production delays, she said, as quoted by Defense News.

2021

Defense News reported on Jan. 20, 2021, that the F-35 was not meeting its mission-capable rate objectives, with figures at the time well short, according to Pentagon acquisition officials. The mission-capable rate was 69 percent, well below the 80 percent goal. The figures for fully mission were 36 percent, short of the 50 percent objective. Officials attributed the low rates to ongoing issues with the canopy of the F-35 and the F135 engine's power module. Spare part shortages have also contributed to failures to meet readiness goals, according to a Government Accountability Office (GAO) report in November 2020.

On April 22, 2021, Defense News reported that the Defense Dept. was pausing work to field a replacement for the ALIS logistics system due to a lack of funding. The F-35 program office had announced plans in 2020 to develop the Operational Data Integrated Network (ODIN), which would combine Lockheed hardware with government-developed software, enabling the Pentagon to retain more control over the system. Due to a 42 percent cut in ODIN development funding in fiscal 2021, the program office decided to take a "strategic pause" in software development for the ODIN, officials said. In the meantime, work would continue to improve the troubled ALIS while ensuring that the ODIN hardware, data environment and software met user needs. It was not clear when ODIN development might resume. Officials said that the program office would update its plan based on available funding, service feedback and a finalized strategy for migrating from ALIS to ODIN. At the same time, ODIN hardware development was continuing. Lockheed had delivered the first hardware kit for testing in September 2020. The new kit was 75 percent smaller and 90 percent lighter than the existing hardware and was projected to cost 30 percent less. It was also demonstrating improved ALIS performance with the kit, including data processing and synchronization that was two to three times faster than the current system. Plans called for fielding additional kits over the summer, which would save money by hosting multiple squadrons on a single unit. At the time, the Defense Dept. planned to invest US$471 million in ALIS and ODIN over the following five years.

Air Force magazine reported on May 24, 2021, that the F-35A's mission-capable rate had increased from 61.6 percent in fiscal 2019 to 76.07 percent in fiscal 2020, despite challenges related to the COVID-19 pandemic. The increase was attributed to additional funding toward spare parts; a larger percentage of the fleet being newer and less problem-prone models; and a greater number of depots available, officials said.

Defense News reported on July 7, 2021, that a new Government Accountability Office report found that, based on estimates at the time, the armed forces would reach a point where projected sustainment costs for the F-35 became too expensive, forcing it to either reduce its planned procurement or significantly reduce flying hours. As Air Force, Marine and Navy F-35 operations reach their peak in 2036, it would be exponentially difficult for the services to sustain them if the cost per aircraft remained at then-current estimates, the watchdog said. The GAO estimated that the Defense Dept. would face a US$6 billion gap in 2036 between actual sustainment costs and the cost that the services could afford. About US$4.4 billion of that would be for Air Force F-35s because the service planned to buy the largest fleet.

Gen. Charles Brown, the Air Force chief of staff, had already indicated that the service might be willing to reduce its F-35 program of record and procure cheaper "fourth-gen plus" fighter to replace its oldest F-16s that were originally to be replaced by the Lightning II.

At the time, total lifecycle cost for the F-35 was estimated at US$1.7 trillion, with sustainment making up around US$1.3 trillion of the figure. The latter represented an increase of more than US$150 billion since the program was rebaselined in 2012 and there was evidence that sustainment costs could continue to increase the GAO said. The Air Force would need to reduce estimated per aircraft per year by US$3.7 million (or 47 percent) by 2036 or it could incur US$4.4 billion in costs above its projections in that year alone.

The Marine Corps would need to cut costs for each F-35B by 26 percent and F-35C by 14 percent or it would face an additional US$900 million in costs above projections in 2036.

The Navy would need to reduce sustainment costs for the F-35C by 24 percent or it will confront an additional US$655 million in costs in 2036.

Air Force officials told the GAO that there was little room in the F-35A program to make reductions in sustainment costs because its design and maintenance plans had been finalized. Meanwhile, Navy officials indicated that they believed that current cost-cutting programs would resolve affordability issues, while the Marines said that they would address any affordability problems in the future. Pentagon officials noted that the services could reduce sustainment costs by shifting additional contractor-performed maintenance to military maintenance personnel.

The F-35 Joint Program Office told the watchdog that service requirements like number of aircraft, flight hours per year and mission-capable rate made it difficult to cut sustainment costs.

Breaking Defense reported on Oct. 7, 2021, that the F135 engine was expected to see an increase in sustainment costs in the mid-2020s as the first powerplants reached the 2,000-hour mark and were sent for scheduled depot maintenance. Pratt & Whitney officials said that they were taking steps to reduce the costs but that it was inevitable that they would rise in the mid-2020s. This would also make it more difficult for the F-35 program to reach its goal of a cost-per-flight-hour of $25,000 by 2025. Scheduled maintenance for the engines would be increasing at the same time that program officials wanted costs to be falling, the officials said. Pratt & Whitney emphasized that the increases were not its fault, due instead to unanticipated wear from operational use, inconsistent funding for spare parts, delays in standing up maintenance depots and the typical churn of engine overhauls, which ebb and flow as the powerplants meet usage milestones. 

The publication noted that the F135 Heavy Maintenance Center at Tinker AFB, Okla., had not been able to repair power modules as quickly as projecting, creating a backlog of work and that engines that frequently operated in hot, sandy environments were grounded after the coating on engine rotor blades cracked and degraded. Pratt & Whitney developed a new coating that had been applied to about 25 percent of the F-35 fleet -- primarily recently completed aircraft. In July, program officials told lawmakers that 41 Air Force F-35As were down and awaiting engine repairs with five others inoperable due to engine issues. As of early October 2021, 42 Air Force F-35As were down due to engine problems. Pratt & Whitney officials noted that additional funding to expedite work at Tinker AFB, set up additional maintenance hubs, buy additional powerplants and change the sustainment architecture would take time to take effect. The depot network was about five years behind schedule because money earlier in the program was diverted to other priorities, the officials said. 

Work at the Tinker depot was improving, according to Pratt & Whitney. While 14 power modules were produced in 2020, it was on track to exceed its goal of 40 in 2021. The time it took to repair a power module had also been reduced from 200 days in 2020 to the objective of 120 days, which would remain the goal for the remainder of the program, said officials. The biggest driver of costs during maintenance is parts and materials, so Pratt & Whitney was focusing on performing engineering work and developing repairs that require maintainers to replace fewer parts during overhauls. Another long-term effort was improving parts and managing the fleet so that engines can remain in the aircraft for longer without requiring depot repairs.

2023

Air & Space Forces Magazine reported on March 2, 2023, that the entire F-35 fleet would receive a retrofit to fix an engine issue that halted deliveries of the jet for two months. Pratt & Whitney had identified the solution. The decision to fix all F-35s was made despite the fact that only a "small number" were affected by the "harmonic resonance" problem. The vibration issue was discovered after an F-35B crash at Lockheed's Fort Worth facility in December 2022. Following the incident, in which the jet suddenly pitched forward during a vertical descent and hit the runway, the F-35 program office stopped accepting deliveries of F-35s and F135 engines and issued flight restrictions for an unspecified number of aircraft. Those aircraft would need to receive the retrofit immediately. The program office also directed that all F-35s should receive the fix within 90 days, although no restrictions would be ordered in the meantime. The decision to retrofit the entire fleet was because the fix was inexpensive, non-intrusive and would maintain a single configuration, a program spokesman said. At the time, F135 engine deliveries had been cleared to resume. Lockheed said it had more than 20 aircraft in storage awaiting authorization for delivery.

Defense News reported on Dec. 6, 2023, that the F-35 fighter's Technology Refresh 3 (TR-3) upgrades were facing significant delays, according to Rep. Rob Wittman, Chairman of the House Armed Services Committee’s tactical air and land forces panel. These delays were expected to impact the subsequent Block 4 upgrade, as TR-3, aimed at enhancing displays, computer memory, and processing power, has been hampered by software and integration issues. Originally set for completion in April 2023, the deadline had been pushed to between April and June 2024. Wittman expresses concern about the delayed rollout, emphasizing that the F-35, a platform of substantial investment, operates below its full capability due to software inadequacies.

The TR-3 technology is crucial for parts of the Block 4 upgrade, which includes enhanced capabilities like carrying more long-range precision weapons, new sensors, improved data fusion, increased interoperability, and advanced electronic warfare features.