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Software and hardware problems have already added millions of dollars to the cost of ongoing F-35 upgrades, and years to the original timescales. At present, there seems little prospect of any imminent solution.

This F-35A Lightning II, seen arriving at Edwards Air Force Base, California, on 1 August 2022, was the first of six F-35s the 461st Flight Test Squadron and F-35 Lightning II Integrated Test Force received to test Technical Refresh 3 and Block 4. (Credit: USAF/Chase Kohler)

The Lockheed Martin F-35 Lightning II family divides opinions. Its manufacturer calls the F-35A “stealthy, speedy and the future of air dominance across the world,” while a recent book about the programme was titled ‘The Trillion Dollar Trainwreck’! The latter was written by Bill Sweetman, a respected analyst and longstanding critic of the programme. Both of these contradictory views have some merit, though today, much of the focus on F-35 is on the problems afflicting the programme. This is, in large part, because difficulties with the Technology Refresh 3 (TR-3) upgrade have led to a suspension of F-35 deliveries. For a whole year, from July 2023, aircraft coming off the production line (because all Block 15 aircraft are being built to TR-3 standards) went straight into storage, pending a solution that will allow the new configuration to be certificated.

In testimony before the House Armed Services tactical air and land forces subcommittee on April 16, Air Force Lt Gen Mike Schmidt, the head of the F-35 Joint Program Office (JPO), admitted that he was: “getting tired of over-promising and under-delivering,” and outlined ongoing problems with the Technology Refresh 3 (TR-3) upgrade. Schmidt said that: “I am as frustrated as you that I can’t nail down a specific date and be extremely clear about exactly when we will deliver,” and acknowledged that: “I need to change that narrative.”

The situation has provoked fury in Congress, with senior members of the House Armed Services Committee arguing for a cut in F-35 procurement in FY25 to 58 aircraft – ten less than the 68 requested by the Department of Defense (DoD), and 18 fewer than the 76 in the House’s FY25 defense spending bill. They wanted to use the excess funds (some USD 526 million) for development, production and testing aimed at addressing F-35 performance issues.

Congressman Adam Smith of Washington, the senior Democrat on the committee, and his colleague Donald Norcross of New Jersey, the senior Democrat on the tactical air and land forces panel issued a statement saying that: “At a projected total lifecycle cost of over $2 trillion dollars, the F-35 is the largest program in DoD history despite routinely not meeting cost, schedule, and performance metrics. This is unacceptable program execution and Congress should not reward this behaviour by buying additional aircraft above the President’s budget request.”

Adam Smith, Chairman of the House Armed Service Committee, asking a question about the F-35A Lightning II during a visit to the 56th Fighter Wing at Luke Air Force Base, Arizona in October 2019. The congressman today is a fierce critic of the F-35 programme.
(Credit: USAF/Tech Sgt Jensen Stidham)

Another congressman, Seth Moulton, earlier attempted to amend the NDAA National Defense Authorization Act to enable the Secretary of Defense to open the F-35 programme up to competition, seizing intellectual property from Lockheed Martin in order to allow other companies to address the F-35′s software problems!

The problems now afflicting the TR-3 upgrade are by no means the first to befall the F-35 programme. As recently as 2019, there were still 13 critical deficiencies, some classified as category 1B issues, (which have a “critical impact on mission readiness”) and others as category 1A (those posing a “risk to the operator’s life”). One of the most unusual was the discovery that prolonged supersonic flight could cause heat damage to the structure and surface coatings of the F-35B and F-35C.

The F-35C is restricted to flying at Mach 1.3 in afterburner for no more than 50 cumulative seconds (the limit resetting after three minutes in ‘dry’ or military power) and the F-35B to flying at Mach 1.2 for 80 cumulative seconds or for 40 seconds at Mach 1.3. This probably prevents the F-35C from being able to reach the optimum Mach 1.44 endpoint for BVR weapon launches.

Other issues included a technical problem with the cockpit pressure regulation system, which caused incidents of extreme sinus pain (barotrauma) in pilots. There were a number of problems with the F-35 helmet, the last to be solved being caused by the night vision camera which could display horizontal green lines that could make it more difficult for pilots to land on ships on nights with little ambient light.

An F-35C Lightning II assigned to the ‘Argonauts’ of Strike Fighter Squadron (VFA-147) in afterburner over Eglin Air Force Base in Fort Walton Beach, Florida. Limitations on afterburner use significantly restrict the performance of the type. (Credit: US Navy/Chief MC Shannon E Renfroe)

TR-3

The TR-3 upgrade should not, on the face of it, have been all that difficult, since it was a relatively modest modification, intended to enable and facilitate the planned Block 4 suite of upgrades. TR-3 was supposed to provide the extra computing power needed for subsequent Block 4 improvements to sensors and weapons, modernising the computational core of the F-35 air vehicle via a new L3Harris integrated core processor, a new aircraft memory unit providing upgraded memory capacity, and increased computer power while also adding updated panoramic cockpit displays. TR-3 will also finally allow the under-performing Autonomic Logistics Information System (ALIS) to be replaced. ALIS is used to manage F-35 maintenance and spares and will be replaced by the new Operational Data Integrated Network (ODIN) system.

Despite its relatively modest scope, technical problems with TR-3 mean that the upgrade is now running three years behind schedule, and has resulted in a USD 330 million increase in the F-35’s development costs, according to the US Government Accountability Office (GAO).

This reflects failures in Lockheed Martin and the JPO’s C2D2 (Continuous Capability Development and Delivery) methodology, and what the manufacturer has called “technical complexity challenges” with both hardware and software. C2D2 was planned to see half-yearly software updates, each with four capability ‘increments’ adding new functionality. This has not been adhered to, and the June 2020 software build consisted of no fewer than ten increments, four of which simply addressed software defects.

General Schmidt told the committee that only 21 of the 52 F-35s that should have been ready for delivery by the end of December 2023 actually contained all of the required TR-3 hardware, and said that two unspecified components had caused a bottleneck in the ramp up of TR-3 hardware production. This was a result of problems in “hardware design maturity,” which had resulted in “low manufacturing yields of parts necessary for aircraft production.” Yet even with these hardware issues belatedly resolved, the TR-3 programme remained mired in difficulties, with flight testing revealing unexpected issues with software stability.

Flight testing of TR-3 began on 6 January 2023, when Major Ryan ‘Bolo’ Luersen of the 461st Flight Test Squadron made the first flight of an F-35 in the Technology Refresh 3 (TR-3) configuration at Edwards Air Force Base, California. The aircraft used was AF-7, 07-0745, an older instrumented flight test aircraft converted to TR-3 standards.

Major Ryan ‘Bolo’ Luersen of the 461st Flight Test Squadron made the first flight of an F-35 in the Technology Refresh 3 (TR-3) configuration at Edwards Air Force Base, California on 6 January 2023 in AF-7, 07-0745, an older instrumented flight test aircraft converted to TR-3 standards. (Credit: USAF)

The 461st Flight Test Squadron (known as the ‘Deadly Jesters’) is the Department of Defense’s lead developmental flight test unit for sensors, weapons, and software on all three variants of the F-35. The squadron received six brand new F-35As from August 2022 to test the Technical Refresh 3 and Block 4 configurations. The six aircraft were required because the complex test missions planned would require a four-ship of instrumented test F-35s with TR-3 (and another four TR-2 aircraft) in order to fully evaluate the aircraft’s warfighting systems and capabilities.

Flight testing quickly revealed that there was a disparity between software stability on the ground, in Lockheed Martin’s fully representative laboratory ‘rigs’, and the stability of exactly the same software when flown ‘live’ on F-35 flight test aircraft.

There is little confidence that a resolution to this software stability problem will be quick or easy, and though in December 2023 General Schmidt told the House Armed Services sub-committee on tactical air and land forces that: “The data tells me [the software problem fix] will be in the middle of spring [2024],” this did not happen, and Schmidt himself admitted that: “I don’t have a super-solid sense that I can guarantee you this date.”

Deliveries planned for July 2023 were pushed back, with Lockheed Martin initially aiming for a new target of April-June 2024. This too has been missed. The first production F-35 in an early version of the Tech Refresh 3 configuration was flown during the week commencing 13 November 2023 at Fort Worth, but it could not be delivered following this initial vehicle system checkout flight, nor the series of acceptance flights that followed. A handful of other TR-3-enabled production F-35s have also been flown, but most aircraft coming off the production line went straight into storage. The JPO said that these initial production test flights would allow the final acceptance flight process to move more quickly when the software is finally approved for operational use.

As recently as May 2024, the GAO reported that the software problems were still ongoing, and that some test pilots had needed to reboot their entire radar and electronic warfare (EW) systems in flight to get them back online.

An F-35A Lightning II arrives at Edwards AFB, California, on 1 August 2022. The aircraft, 20-5578, is the first of six F-35s destined for the 461st Flight Test Squadron and F-35 Lightning II Integrated Test Force. (Credit: USAF/Chase Kohler)

The Lot 15 F-35s have all been built with TR-3 hardware embodied, but the DoD customer has refused delivery of all aircraft built to this standard until the software is cleared. New aircraft were instead placed in storage from July 2023. Lockheed Martin built approximately 158 F-35s of all versions during 2023, but delivered only the 98 aircraft built as Block 14s.

It is known that the 60 Block 15 aircraft built in 2023 were placed into storage pending the TR-3 software update being ready, together with those built in the first half of 2024. The number of aircraft in store is growing with the passage of time. Further older aircraft may have been stored waiting for a (now delayed) retrofit of TR-3.

Schmidt refused to confirm how many F-35s are being stored, but allowed that it represented a “significant number.” In January 2024, Lockheed Martin said that the number of aircraft in store could soon reach 100-120 aircraft, but predicted that it would begin delivering TR-3 equipped aircraft during the third quarter of 2024 (between July and September).

The pause in deliveries has affected different customers to a varying degree. Belgium, for example, faces a potential fighter gap, as its first aircraft are TR-3 standard F-35As, and can’t be delivered, and yet the retirement of its existing F-16s is already underway. Denmark faces a similar problem, with just four TR-2 jets based at Skrydstrup. Six more, now stationed at Luke Air Force Base in Arizona for training, will be transferred to Denmark to bolster the force as the RDAF F-16 force winds down. By contrast, the Netherlands anticipated delays and in late 2022 requested that its next six aircraft should be delivered in the TR-2 configuration rather than waiting for the TR-3 version, allowing deliveries to continue through to March 2024. The Dutch expect to get their first TR-3 configured F-35 in late 2024, and expect only a “limited impact” on the RNLAF’s plans to stand up a third Dutch F-35 squadron in mid-2027. The Pentagon has reportedly withheld payments on the sequestered aircraft, but it is not known whether any export customers have similarly refused to pay due instalments.

Subject to agreeing terms and conditions with Lockheed Martin, and assuming that a stable, capable, maintainable software version can be achieved, the F-35 Joint Executive Steering Board (JESB), representing the US and international F-35 partners and customers) has agreed to the criteria under which they would accept an interim, ‘truncated’ version of TR-3. This will not include all the planned capabilities, but would be safe, stable, and useful for training. Even such an interim truncated TR-3 software standard would need to be proven to be stable and airworthy, however.

A Royal Danish Air Force F-35A Lightning II fighter jet assigned to the 308th Fighter Squadron, Luke Air Force Base, Arizona, flying over Bagdad, Arizona, on 5 May 2021. The RDAF is to redeploy its US-based F-35As to Skrydstrup, to compensate for late delivery of its TR-3 configured aircraft. (Credit: USAF/Airman 1st Class Dominic Tyler)

Under the new plan, the TR-3 software would be released in two separate drops, with the first being the truncated version, release 40P01, for training only. The final, fully combat-capable software load (40P02) should follow about one year (12-16 months) later, assuming that they get the truncated release ‘right first time’, without needing incremental software releases to test and implement critical fixes. But there is (and can be) no ‘hard’, set-in-stone timescale, since every additional, incremental release would add a delay of between two and six weeks. There is known to be a real worry among export customers that Lockheed Martin may be tempted to drip-feed “a salad of interim halfway solutions and different versions” into the production pipeline creating an unmanageable configuration control problem, according to a senior officer in a customer air force.

Rob Wittman, the Chairman of the Tactical Air and Land Forces Sub-committee has said that he believes there would be some “utility” in delivering F-35As with just such a truncated TR-3 capability, offering a useful training capability even if they lacked full ‘combat coding’. In the interim, existing TR-2 training aircraft could easily be combat coded.

Block 4

While the TR-3 upgrade will be successfully concluded, (eventually), things look rather less certain insofar as the planned Block 4 upgrade is concerned.

The Block 4 upgrade was originally conceived as a means of keeping the F-35 operationally viable, ensuring that the F-35 retains its ‘edge’ by enabling particular future capabilities and weapons while also increasing cross-platform interoperability.

In order to ensure that the F-35 will be able to continue to defeat peer level threats and bring its pilots home safely, Block 4 was optimised to counter emerging Chinese and Russian air- and ground-based threats, and originally encompassed some 53 improvements including new weapons integrations and new or enhanced software features, and more powerful data fusion.

Northrop Grumman is developing the AN/APG-85 AESA radar for the F-35 as the successor to the AN/APG-81 AESA radar currently in use. (Credit: Northrop Grumman)

The upgrade originally included 11 sensor (radar and optronics systems) enhancements, including a new Northrop Grumman AN/APG-85 radar (for US aircraft at least). Block 4 was also intended to add radar enhancements for the extended surface warfare mission, with improved maritime surveillance, identification and targeting performance. The new AN/APG-85 radar will probably incorporate Gallium-Nitride (GaN) TRMs, allowing it to produce more power while generating less heat, while providing better capabilities against difficult air targets.

The Block 4 upgrade also included 13 EW updates (including an upgraded BAE Systems AN/ASQ-239 EW suite). There were also seven interoperability and networking enhancements and seven cockpit and navigation upgrades, eight logistics and support system changes.

New long-range and precision guided munitions (PGMs) expected to be integrated on the Block 4 aircraft included the Raytheon AGM-154C1 Joint Standoff Weapon (JSOW) for US Navy F-35Cs, and the Kongsberg Joint Strike Missile (JSM), the Roketsan SOM-J cruise missile, the Raytheon GBU-53/B Small Diameter Bomb II (SDB II), as well as the MBDA Meteor and SPEAR weapons (together with internal carriage of ASRAAM, which is already cleared for external carriage).

In June 2018, the Government Accountability Office recommended that a Block 4 contract award should be delayed until initial operational testing was complete, but this recommendation was ignored, and the JPO placed the contract in November 2018, citing the urgent risk posed by the rapid advance of threat systems. This set the scene for exactly the same kind of ‘concurrency’ that has plagued the core F-35 programme.

The Block 4 upgrades were originally expected to be rolled out via staged half-yearly updates every April and October. These were due to begin in 2019 and were to have continued until at least 2024, though these dates soon slipped. Vice Admiral Mathias W. Winter, the previous F-35 Program Executive Officer, had stressed that Block 4 should be “technically feasible while operationally relevant.” Yet Winter’s advice went unheeded, and the scope of the Block 4 upgrade also increased over time, going from 53, to 66 and then to more than 80 major changes as the design was progressively adapted to meet an ever more rapidly evolving threat.

Schmidt told the House sub-committee that an independent review in 2023 had determined that “numerous Block 4 capabilities will not deliver until the 2030s”. This is years later than the most recent estimates provided by congressional auditors, and as a result, the Block 4 upgrade is to be “re-imagined”.

Efforts to integrate non-US armaments such as the MBDA Meteor air-to-air missile (pictured, right) with the F-35 have faced delays. (Credit: Jamie Hunter/MBDA)

The exact content of the re-imagined Block 4 has not been defined – and may not yet have been decided, and it remains to be seen how some customer nations react (those who signed for the delivery of Block 4 aircraft, understanding that designation to have a specific meaning, with defined capabilities). Schmidt did not elaborate as to what the re-imagined Block 4 upgrade would include, but he did say that the upgrade would require a ‘buy-in’ from all members of the F-35 enterprise, suggesting that the re-imagined Block 4 might lack significant features compared to the original Block 4 that they had signed up for.

General Schmidt did say that the re-imagined Block 4 would include “common capabilities for electronic warfare; communication, navigation, and identification; sustainment, and new weapons for the partnership, plus US service-unique capabilities and partner-unique capabilities.”

The re-imagined Block 4 upgrade will focus on “what industry can actually deliver”, providing “must-have content,” consistent with the JESB-directed development funding cost cap, according to Schmidt. Sub-committee Chairman Rob Wittman added that: “I want it (the Block 4 plan) to reflect reality. I want them to understand what can you do realistically.” The re-imagined upgrade will reportedly include an undefined subset of 88 capabilities which have been described as “those which give us the most bang for the buck,” to be delivered in “a combat relevant timeframe,” Schmidt said.

Particular hardware and software insertions will be tied to agreed ‘capability decision points’ (CDPs) across the Future Years Defense Program (FYDP). General Schmidt has said that: “Lessons learned in the execution of the TR-3 program will be applied across the entire Block 4 modernization programme.”

The Block 4 upgrade will require more electrical power and improved thermal management, and at one time was expected to receive an all-new engine. Under the Adaptive Engine Transition Program (AETP) Pratt & Whitney and GE Aerospace were given contracts to develop new adaptive cycle engines for the F-35, and in 2022 the two companies delivered prototype AETP engines to the US Air Force for testing and evaluation. The new engines each offered a massive increase in performance, and the General Electric XA100 engine promised to deliver at least 20% more thrust and 30% more range than the current Pratt and Whitney F135-PW-100 engine. Unfortunately, the cost of re-engining the fleet, and problems adapting an AETP design to the F-35B, led to the entire AETP programme being summarily cancelled. Instead, the JPO has started work on a more modest F135 Engine Core Upgrade (ECU) as well as an associated programme to improve the aircraft’s power and thermal management system (PTMS).

An F-35C test aircraft CF-2 makes that variant’s first night flight on 13 June 2012 at Naval Air Station Patuxent River, Maryland. The F-35 engine is already inadequate to meet the aircraft’s electrical power and cooling requirements, and TR-3 and Block 4 will exacerbate the problem. Plans for a new engine have been abandoned, and instead a more modest F135 Engine Core Upgrade (ECU) has been commissioned, together with an associated programme to enhance the power and thermal management system (PTMS). (Credit: Lockheed Martin)

There are concerns in some circles that the re-imagined Block 4 upgrade will reflect US warfighter priorities, and that this could be extremely bad news for anyone waiting for the integration of their own indigenous weapons, or for other ‘partner unique capabilities’. For the UK, there are now real doubts as to when the MBDA Meteor BVRAAM and SPEAR 3 missile will be integrated, and some suspect that these weapons may never be integrated.

The wider picture

Despite the difficulties and problems, the F-35 is, without doubt, the most survivable combat air and ISR platform in service today. If the task is to go and drop a pair of small PGMs through someone’s roof, and return home safely (probably undetected, and certainly unmolested), then there is no better aircraft to achieve that than an F-35. The F-35 also has an unmatched ability to gather up a detailed tactical picture, using its sensors to provide its pilots with unrivalled situational awareness. The aircraft also has formidable electronic attack capabilities, offering another way of overcoming enemy air defences.

Yet many believe that even with Block 4 successfully embodied, the F-35 will have a limited ‘window of superiority’, and that it cannot be upgraded sufficiently to remain at the top of the air power game for much longer. Many believe that even an upgraded F-35 will be inadequate to meet the rapidly evolving and increasingly contested threat environment.

Jonathan Smith, VP Capability and CTO, Future Combat Air (GCAP), for Leonardo UK’s Electronics Division, is one of the few men to have flown both the F-22A Raptor and the F-35B Lightning II operationally, and has served as the UK F-35 Lightning II Tactics and Development Staff Officer, before becoming the Executive Officer and later the Commanding Officer of No.17 Test and Evaluation Squadron, the UK’s Test and Evaluation Squadron for the F-35B, at Edwards Air Force Base, California. Returning to the UK, Smith became the UK F-35B Requirements Manager, Air Capability from June 2019 to April 2020.

Smith described today’s F-35 as being: “A tool designed for a job and one that does that job very well.” However, he added, “The ability of the F-35 to do that job in a future context is going to be significantly challenged. Yes, the F-35 is very good, but it was designed to do something in a constrained epoch that we’re now moving out of.” Tomorrow’s contested environment will make today’s operating environment look almost benign, Smith believes. “The threat picture is getting harder, and it’s getting harder, faster.”

A US Marine Corps F-35C Lightning II assigned to Marine Fighter Attack Squadron (VMFA) 314, Marine Aircraft Group 11, 3rd Marine Aircraft Wing, and two AGM-154 Joint Standoff Weapon (JSOW) are staged at Marine Corps Air Station Miramar, California, on 8 March 2024. (Credit: USMC/Sgt Sean Potter)

Smith believes that the F-35 will remain relevant only in the way that fourth-generation fighters are useful today – most relevant and most effective when operating within a combat air ecosystem populated by additional tools, such as Next Generation Air Dominance (NGAD), Tempest and Future Combat Air System (FCAS). The F-35 will be the ‘low end’ platform in tomorrow’s high:low mix, augmenting the new ‘sixth generation’ platforms. These new fighters are, he said, being “designed and developed to meet a specific challenge in a specific time that maybe you can’t quite iterate an F-35 up to. You can’t continually expect your current platforms to meet to meet the threat context and meet the performance levels that you need as time goes by.”

Smith said that: “When you look at the F-35, yes, it’s a fantastic platform, but it will increasingly have its limits and where those limits appear, we have to have something that can fill those capability gaps. There’s no doubt about it.”

Smith believes that: “The Americans are the best proponents of having the right tool for the job, and that’s why NGAD is being invested in so heavily – because they see a gap in capability. I think it was Gen Nahom who said, a couple of years ago, that they need a platform that can project power further for longer. You could do a bunch of things to F-22 (or F-35), but it just cannot fundamentally achieve that, which is why they’re developing NGAD.”

Perhaps the best thing about the re-imagined Block 4 programme is that it could (or should) pioneer the approach that will shape how the next generation NGAD programme is run. General Schmidt said that: “Block 4 ought to be an experience that can not only get us further in the software design and upgrades for F-35, but it also should inform what we’re doing in digital design and digital twin development.”