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Commentary on Likely Increase in JSF Engine Costs to Increase - Part 2

Air power discourse is The Central Blue’s core focus. In this two-part series, Gary Waters provides an in depth commentary on likely increases to the F-35 Joint Strike Fighter engine costs. This discussion continues the conversation of a recent Breaking Defense article, providing an Australian perspective around important air domain elements of sustainment. In Part 1, Waters takes us through the Breaking Defense article and highlights some of the challenges the F-35 faces. Here in Part 2, he explores what can be done and how sustainment efforts for the aircraft and its engine are likely to play out.

Broad Observations from the Breaking Defence Article

With that discussion as background, a number of ex-RAAF aerospace engineers came together online to consider these engine affordability challenges and made several relevant observations.

First, there are several pertinent points that are evident in this F135 cost increase, which should be noted:

  • This engine is an outgrowth of the F119 engine fitted to the F-22.

  • The F135 is a 40000 lb thrust engine, whereas the F119 is a 30000 lb thrust engine.

  • Given the size of the F135 is almost the same as the F119, the engine has to work harder to produce the thrust.

  • Working harder means higher temperatures, pressure and vibrations throughout the engine, increasing wear and tear, and the chances of parts failing earlier than predicted (e.g., the turbine blade coatings not surviving as long as expected in dry and dusty environments). Additionally, this engine produces potentially damaging low frequency vibrations when in afterburner that have yet to be dealt with.

Second, RAAF engineers experienced similar engine reliability issues in the mid-1980s, with the TF30 engine in the F111s. In Australia, engine failures required the removal of the engine around every 500+ hours, which caused significant disruption to operational availability, and overwhelmed the RAAF engine repair / overhaul facility at Number 3 Aircraft Depot. Comparably, in the United States, the USAF F111 units reported engine failures that required their return to Tinker at a significantly higher rate. This difference was quite marked, and was due to cost pressure on the US repair / overhaul facility that meant engines were repaired and tested to ensure they met only the minimum acceptable performance level on release to the unit. Engines that failed this test were further ‘tweaked’ to meet the target. The RAAF approach was to repair and test to ensure the engine met as close to the maximum level of performance as possible, thereby providing the potential to be installed for longer periods with normal ‘wear and tear’.

The different approaches were driven by the budget that the USAF operational unit allocated to engine repair / overhauls (each unit was allocated a flying hour rate, an operational readiness target, and a budget to achieve it – breaching any of these had serious consequences), whereas RAAF Squadrons simply requested an engine repair / overhaul and did not need to concern themselves with the cost.

As a general comment, this highlights an underlying problem with any budgeting system that allocates an arbitrary budget – making it almost impossible for an operational unit to prepare for high-end operations. Certainly, there is no way any commercial organisation can address such a self-imposed constraint, especially as they address their own challenges of performance and cost optimisation.

Third, with these F135 challenges in mind, and noting that the F-35 will need an improved engine (more power and cooling) to support upcoming Block 4 enhancements to make the F-35 more lethal, a significant increase in engine capability at a more affordable price is very enticing. Thus, it will be interesting to see if the JSF Program Office re-introduces competition, noting that the Pentagon stopped funding General Electric’s F136 engine in 2011. Competition would also likely see re-energised efforts at reducing engine maintenance costs.

General Electric Aviation would offer its XA100 adaptive-cycle engine, which the company is developing as part of the US Air Force’s Adaptive Engine Transition Program (AETP). There are two prototypes under test so far. General Electric anticipates that the XA100 will increase the F-35’s range by 30 percent, increase thrust by 10 to 20 percent and improve fuel burn by 25 percent when compared to current engine performance. In addition, its thermal management capability would be doubled due to the third stream of air flowing through the XA100, which acts as a heatsink for electronics, avionics and mission systems. That would give the F-35 the cooling it needs to accommodate the upgrades planned as part of Block 4, with margin for additional advances. However, the XA100 — like other adaptive engines — is still moving through development and won’t be ready until 2027 at best.

Pratt & Whitney also has an adaptive engine in the works (the XA101), which it is developing as part of the AETP effort.

It is important to point out that a new engine would require considerable Operational Test and Evaluation (OT&E) before acceptance. Additionally, a new engine would potentially require structural modifications to accommodate it, as well as mission system software changes to accommodate change in fuel flow management, and weight and balance issues. A 2027 date would seem optimistic.

Pratt & Whitney is also proposing an upgraded version of the F135 that would provide an increase in thrust and power management, offering a more economical improvement plan for the F-35’s engine. This most expansive suite of upgrades would increase the F135’s range and thrust by as much as 10 percent, while doubling the engine’s thermal management capability. An upgraded version of the F135 would mean that a new engine does not come into the mix, with its attendant costs, nor is there a mixed fleet of adaptive engines and F135s.

The performance improvements of these various options are discussed in Valerie Insinna, ‘F-35 Engine Rivals Prepare for Another Clash’, Breaking Defense, 15 October 2021.

As a point of clarification, engines built for fighters prioritise thrust, whereas commercial airlines prioritise fuel efficiency. Adaptive engines can shift between the two modes — allowing a fighter to use less fuel as it cruises and hence improving its range, but also affording it the thrust it needs during combat.

Fourth, and related to the OT&E comment above, it appears that industry is expected to take all the risk on Test Equipment and stand-up costs for deeper level maintenance of the components of the aircraft, noting that the RAAF bought all the test equipment for the F/A-18s and other aircraft and supplied it as GFE (Government Furnished Equipment) to the commercial providers. The RAAF was the contracting party in these cases, whereas with the F-35, the US Joint Program Office is the contracting party. On the current trajectory, it is difficult to see much of the component work being done in Australia.

Fifth, while sustainment issues always arise as new aircraft are operated, and effects flow through from limited-rate production contracts, the slow-rate production of spare parts, a slow-rate production for depot stand-up, and demanding customers, the US government and the F-35 partners did sign up to the memorandum of agreement. With no other viable contender, there was always going to be a challenge if a large company like Pratt & Whitney did not take a calculated risk to initiate long-term contracts with its suppliers and also invest in early set up of depots.

Finally, engines may not be the only area that will be of concern for the F-35. Most of the costs will be in the software and the reprogramming laboratories for the mission data files, so it will be important to optimise these costs. Sustainment cost increases might also arise with the stealth performance. Notwithstanding design efforts to ‘bake in’ stealth coatings to composite parts, like any aircraft system, the F-35 is subject to wear and tear associated with environmental and operational issues. There will be ongoing costs associated with monitoring, measuring and conducting repairs, as well as improving the F35’s stealth capability.


While this Commentary has focussed on JSF engine affordability, it has also pointed out that the challenge of cost optimisation extends beyond engines. Challenges around F-35 sustainment will increase as the aircraft accumulates mission hours, and it is incumbent on the RAAF to prepare for this, to ensure that this jewel in the crown of Australia’s defence capability (the JSF), remains just that.

Gary Waters spent 33 years in the RAAF, resigning as an air commodore and joining the Australian Public Service at the Senior Executive level. After four years in the public service, Gary became head of strategy for the Australian arm of a global defence company, retiring seven years later. He now consults on a part-time basis. He has a PhD in political science and international relations and has written extensively on defence, air power and cyber issues.


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