Lawmakers oppose complete engine replacement for F-35 fleet

As the Pentagon continues weighing its propulsion modernization options for the F-35 Joint Strike Fighter, three-dozen lawmakers have banded together to oppose a potential complete engine replacement for the program.

In a letter to the Defense Department’s acquisition chief, the members of Congress instead rallied behind an engine upgrade plan floated by F135 maker Pratt & Whitney that would incrementally roll out updates across the entire fleet.

“The F-35 program is already the most complex and expensive program ever undertaken by the Department,” lawmakers wrote in the July 22 letter. “As the program begins to shift from development and production to long-term sustainment, we believe that now is not the time to initiate a complete engine replacement program.”

Already two decades into the program, DOD officials are facing a need for enhanced F-35 power and cooling tied to forthcoming capabilities, with those upgrades expected to result in more bleed air extraction than the level that was originally planned.

While Pratt supports upgrading the current propulsion system, the company is also one of two engine makers developing solutions for the Air Force’s Adaptive Engine Transition Program. Through that push, both Pratt and General Electric are maturing prototypes compatible with an F-35A conventional takeoff and landing variant. GE has advocated for a follow-on engine to the F-35.

In the letter, lawmakers raised concern over what they characterized as Air Force Secretary Frank Kendall’s plans for the service to pursue “a costly, risky, and unproven [AETP] engine as a replacement for the existing” one.

The Air Force has not announced its engine modernization plans, as officials are continuing to await the results of analyses to help determine their path forward. The F-35 Joint Program Office is poised to wrap up its business case assessment, which will review proposed engine and power and thermal management system solutions, and brief the Joint Executive Steering Board on the results in September.

Meanwhile, the Air Force is doing its own operational analysis of its engine modernization options, including a look at the costs and affordability of leveraging an adaptive engine for the F-35A, officials noted in past testimony submitted to Congress.

Kendall during a hearing before the House Armed Services Committee in April pushed back on concerns the service was looking to fund a second F-35 engine through the program, saying the effort was “a completely new and much-improved F-35 engine, potentially.” In that same hearing, he said AETP has more than $6 billion in costs tied with development and the transition into production -- a figure legislators cited in their letter.

The document also stressed the potential lack of a shared engine solution, maintenance and supply pipeline that would come if the Air Force were to go it alone with a replacement option, as well as the challenges of retrofitting an AETP onto an F-35B variant. GE has previously said it has a “compelling offering for the F-35C" carrier variant, and DOD is currently assessing the “tri-variant viability” of adaptive engines for the fleet.

"The cornerstone of the JSF program has been, and remains, commonality,” lawmakers wrote. “To enable global common maintenance, training, and supply chains, the JSF program relies on a common airframe platform featuring different variants capable of a service’s unique mission and powered by a common engine across our Military Services and international partners. This commonality would optimize joint operational effectiveness while creating economies of scale to control sustainment costs.”

In addition, the letter raised concerns about the possible risk to pilot safety if an engine replacement is pursued, as well as “how a major change to the F-35 program, such as a replacement engine, will impact the industrial base.”

Led by Rep. John Larson (D-CT), the letter asks William LaPlante, the under secretary of defense for acquisition and sustainment, about the timeline for requirements surrounding propulsion modernization, and whether DOD plans “to conduct an independent comparative analysis and cost assessment of the F135 engine modernization options” or review the potential impacts on the industrial base. Pratt’s headquarters is in East Hartford, CT.