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An F-35B Lightning II aircraft assigned to Marine Strike Fighter Squadron (VMFA) 121 launches from the flight deck aboard amphibious assault carrier USS Tripoli (LHA 7), July 1, 2022.

An F-35B Lightning II aircraft assigned to Marine Strike Fighter Squadron (VMFA) 121 launches from the flight deck aboard amphibious assault carrier USS Tripoli (LHA 7), July 1, 2022. (Peter Burghart/U.S. Navy)

Daily, the news brings confirmation of America’s need for strong national defense. Russia continues a bloody, unjustified war against Ukraine to re-create the old Soviet Union. China teeters on economic collapse, potentially making the threat of Taiwan’s invasion a reality to distract from the self-inflicted economic catastrophe. It is a demanding time, and America must be vigilant and efficient in marshaling resources for our national security.

Soon, the House and Senate will face that challenge in the committee “markups” for the fiscal year 2023 National Defense Authorization Act. Difficult decisions will be made to determine the direction, capability and cost of U.S. security. Included within the NDAA is the flight path of the F-35. Congress will decide whether to fund an upgrade to the current Pratt & Whitney F135 engines or replace them with the conceptual Adaptive Engine Transition Program engine in the F-35. Choosing the latter option could prove to be a costly decision.

F135 engines power the fleet of approximately 700 delivered F-35s and are planned for another 1,000 plus F-35 aircraft. The F135 was variably designed for the three different missions. U.S. Air Force and foreign customers have purchased the classic takeoff version F-35A while the U.S. Marines acquired the F-35B short takeoff-and-landing variant and the U.S. Navy procured the F-35C carrier option. Logistics, supply chains, training and maintenance support for the F135 engines have been established and are currently operating in support of each of these missions. 

AETP’s goal is to transform the performance of jet engines for the Next Generation Air Dominance aircraft by improving fuel efficiency by 25%, increasing thrust by 10% and reducing engine heating to allow for more sorties to be accomplished with greater range using the same amount of fuel. Like other current military jet engines, the F135 has two coils of air, one for maximum power and one for fuel efficiency. AETP adds a third stream of cooled air around the engine that can be diverted to switch from fuel efficiency to performance or vice versa. 

Planned air vehicle growth in the F-35 means that the current thrust, power and thermal management capabilities of the F135 will be exceeded by the end of the decade; triggering the upgrade vs. replace discussion. In 2020, P&W was awarded a contract for F135 modernization which they dubbed the F135 Enhanced Engine Package, but some in the Pentagon and Congress are now looking to revive the AETP program again. This appears to be redundant as the proposed retrofit to the F135 engine will provide the needed performance upgrades.

For example, the F135 engine generates 43,000-pounds of thrust, which means the engine runs at high temperatures to generate maximum power. EEP thermal management allows the engine to better cool itself, similar to the AETP three-stream engine technology. P&W claims this and other upgrades provide the fighter more capability without sacrificing power. EEP asserts improved thrust and range by more than 10% each, a 50% improvement in thermal management and affords the F-35B a 5% boost in vertical lift — all sustained by the current supply chain and logistical systems. 

There are other prohibitive factors that make sense for EEP selection. The first is AETP is not an F-35 requirement. Making it a requirement demands F-35 program changes including the statement of work, updated contractual requirements, a series of Class I negotiations, rewritten technical publications, planning for additional training and new maintenance processes. This is a long process demanding supplementary dollars and delivery delays.

Furthermore, the AETP is designed to meet the requirements of the Next Generation Air Dominance, not the F-35. To adapt the AETP to the F-35 would require redesign of the engine envelope, interfaces, such as pneumatics, fuel lines, attach points, etc. plus additional RDT&E. Even after all that additional cost, the AETP won’t fit on the F-35B at all nor the F-35C without significant pricy modifications from the F-35A version. In addition, this would shift all additional AETP costs to the Air Force’s limited budget and foreign allies purchasing F-35As whose contracts would likely need renegotiation for added costs.

Next are the problems with fielding a second engine for the F-35. Brig. Gen. Dale R. White, Air Force program executive officer, has said, “trying to change a powerplant in … a fielded system is extremely complex. …You have to think about what the return on the investment might be.” In short, two separate F-35 engines mean dual supply chains, training, maintenance, logistics and other added costs to an already expensive over-budget program.

Some rough cost estimates of adding the AETP to the F-35 put the price tag at a prohibitive $40 billion. In a Government Accountability Office report on the F-35 the program is already eight years behind schedule and over $165 billion over budget. It would be difficult for Congress to justify the added value of incorporating the AETP engine into the F-35 program. Given all the challenges to program schedules and added dollar outlays, a second engine for the F-35 just doesn’t make good sense. 

Todd Tiahrt, a Kansas Republican, served on the House Appropriations subcommittee on defense during his time in the U.S. House of Representatives.


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