Raytheon Technologies‘ [RTX] Pratt & Whitney held a supplier day Feb. 28 on Capitol Hill for the company’s proposed F135 Engine Core Upgrade (ECU) for the Lockheed Martin

[LMT] F-35 fighter–an event attended by more than 80 supplier representatives from 24 states, Raytheon said.

DoD’s upcoming fiscal 2024 budget request is likely to lay out a future path for the engine for future blocks of the F-35. Raytheon is trying to build the case in Congress for the ECU, which is vying with General Electric‘s [GE] XA100. The Pentagon may decide to upgrade the F135 or build a new engine to accommodate new weapons and other upgrades envisioned for Block 4.

Jen Latka, Pratt & Whitney’s vice president of F135 programs, told reporters on Feb. 28 that the F135 suppliers’ “commitment to this program is vital to ensuring that the ECU delivers the thrust, the range, and the power and cooling that is needed to enable Block 4.”

“There is no formal requirement, but we are modernizing [the engine] because of a power and cooling challenge,” she said. “As the air vehicle is upgraded and more mission systems are coming onto the jet, they require more power, more cooling, and so the engine needs to be upgraded commensurately.”

Last week, the F-35 JPO said that the program would undertake mitigation measures to ensure that “harmonic resonance”–a higher than normal engine vibration–did not affect the operation of the F135 engines (Defense Daily, Feb. 24).

So far, “harmonic resonance” appears to have been a rare occurrence in a relatively low number of fighters with fairly new F135s.

“Following an aircraft inspection in December, 2022, a safety concern was identified with the F135 engine,” the F-35 program said last week.

“Since December, Pratt & Whitney along with engineers from the JPO, Lockheed Martin, Naval Air Systems Command (NAVAIR) and the Air Force Lifecycle Management Center (AFLCMC) have worked tirelessly to understand and develop mitigations for a rare system phenomenon involving harmonic resonance to develop a path forward for safe operation of the F135 in flight,” the F-35 JPO said. “The actions the government and industry team are taking will ensure incorporation of mitigation measures that will fully address/resolve this rare phenomenon in impacted F135 engines. At this time, the JPO has authorized the resumption of engine deliveries to the production line.”

The F-35 JPO, Lockheed Martin, and Pratt & Whitney have not identified the “mitigations” to alleviate engine harmonic resonance.

In December, Lockheed Martin and Pratt & Whitney halted deliveries of the F-35 and the F135 engine after the pilot of a Lockheed Martin-owned F-35B ejected on the runway at Naval Air Station Joint Reserve Base Fort Worth, Texas on Dec. 15 (Defense Daily, Jan. 3).

“As a government-industry team, we have been working since then around the clock to understand it, develop mitigations for a very rare systems phenomenon involving ‘harmonic resonance,'” Latka said on Feb. 28.  “We have been able to field one of those mitigation actions, and we are pleased to report that [F135] engine deliveries resumed on Feb. 18.”