U.S ponders ‘Adaptive Technology Engines’ as F-35 retrofit

Adaptive technology engines promise great performance but come with technology, financial and interoperability risks

With over 700 aircraft operational the F-35 is becoming the centrepiece of air forces and navies across the globe. Not only is the aircraft itself a stunning success with its range of unmatched stealth and strike capabilities, but it is a remarkable exercise in international interoperability.

This article was contributed to the UK Defence Journal by James Maclaren. Maclaren is a freelance journalist and writer specialising in defence and security. He is a former UK military officer with command, staff, joint experience in a variety of roles and operational environments. He is based in London.

This article is the opinion of the author and not necessarily that of the UK Defence Journal. If you would like to submit your own article on this topic or any other, please see our submission guidelines.

Any potential adversary must reckon with the force multiplication effect of taking on combined forces with seamless operational and logistic capability.

It is no surprise that generals and politicians alike see the aircraft as a battle winner which with its beyond peer shoot and sensor capability will provide an air power lead for some years to come. The propulsion system is at the heart of the aircrafts stealth capability and in a platform as complex as the F-35 maintaining its edge over emerging Russian and Chinese competition means extending endurance performance and efficiency is a pre-requisite for the anticipated four decades the aircraft is expected to be in service.

However, while nothing about the F-35 can be said to lack ambition, a complete retrofit of the aircraft’s propulsion system was probably not envisaged. But this is what some senior leaders in Congress and the Pentagon are raising as the bold route to achieve future capability aspirations. It is a controversial proposal and has attracted disquiet for the risk such a complex and expensive change to the aircraft life cycle would have, particularly as a Pratt & Witney planned engine upgrade proposal goes a long way to achieving the necessary operational capability.

The proposal originates in a programme designed to support sixth-generation fighter technology the Adaptive Engine Transition Program (AETP). Both Pratt & Witney and General Electric have programmes to bring new technology propulsion into service, principally to meet the operational requirements of the next generation clean-sheet F-16 replacement. However, growing voices propose that this technology, still in development, could be retro fitted into the F-35 fleet, specifically the F-35A variant whose major customer is the USAF as well as allied air forces across the globe. The merging of AETP in theory would catapult F-35 endurance and performance to new levels.

Opponents of this idea point to the risk that a retro fit may just not be technically possible. There will be complex engineering and technology hurdles to overcome and rejecting current upgrade programmes in favour of untested technology risks a world beating fighter stagnating as its propulsion system waits for replacement. There is also the significant financial risk. No current budget for fleet replacement exists and procurement executives will view with anxiety attempts to bring AETP into the already hugely expensive F-35 programme. Whatever initial projections are, the reality is almost certain to be considerably more expensive. 

While the debate has so far been mostly confined to the technical media in the United States, almost certainly the initiative will have raised concerns in allied operators of the aircraft who will be conscious of the supply chain implications and wary of the cost implications of AETP which is likely to be passed on in one form or another.

The United Kingdom has a special interest, although it is currently keeping diplomatically quiet. It is the only Tier one partner in the F-35 program. Alongside the United States Marine Corps, and after considerable debate, it operates the F-35B, the short takeoff/vertical landing (STOVL) variant on its new carriers. This decision results in operation of a F-35 variant not currently believed suitable for AETP retrofitting and for which the planned production numbers are considerably less than either the F-35A and F-35C.

The danger for the United Kingdom and other F-35B operators is that this variant will wither, with programme resources directed towards AETP variants and with the commonality required for efficient supply chain management and operations reducing drastically. The RAF/RN and their counterparts in the USMC could end up with a poor cousin of an aircraft while the increased cost of an AETP equipped aircraft could have serious implications on the smaller operators of the F-35A.

A powerful advocate for the retrofit of AETP includes the Secretary of the Air Force Frank Kendall, who previously has been highly critical of F-35 cost over runs. As the single largest operator of the F-35 the single service drive towards AETP carries considerable influence to Congress. But the debate is finely balanced with many acknowledging that selecting AETP over the existing Pratt & Witney proposal exposes the programme to immense engineering, logistical and procurement risk. 

A major strength of the F-35 programme, in spite of its immense cost has been that it meets the operational requirements of ten militaries to date, with more buyers waiting in the wings. The pursuit of propulsion perfection may compromise that success. How much that will weigh upon the decision making of the US Department of Defense remains to be seen.