While General Electric‘s [GE] proposed XA100 Tri-Variant Adaptive (TVA) for the F-35 has a degree of commonality with the company’s XA100 design for the U.S. Air Force F-35A, adapting the XA100 engine or a derivative of it for the U.S. Marine Corps’ F-35B short take-off and vertical landing (STOVL) aircraft would require a separate development effort, per the F-35 Joint Program Office (JPO).

GE has said that it began working with the F-35 JPO in the fall of last year on evaluating whether GE could alter its proposed XA100 engine for the U.S. Air Force’s Adaptive Engine Transition Program (AETP) to fit on the F-35B (Defense Daily, June 23). GE targeted the submission of an interim report to the F-35 JPO before this month’s meeting of the JSF Executive Steering Board (JESB) and has said that the company will submit a final report by the end of the year.

The company “performed a study with the F-35 JPO and the AETP program Office to see if the XA100 or a derivative thereof could be adapted to work in the STOVL F-35B,” the F-35 JPO said this week. “The resultant XA100 TVA is based on the current CTOL [conventional take-off and landing] F-35A XA100 and maintains a level of commonality, but is significantly different enough that it would require its own independent EMD [engineering and manufacturing development]  The report cannot be released since it is GE proprietary and potentially source selection sensitive.”

GE did not disclose the total nor specific projected costs of the independent EMD, but the company did say that adapting the XA100 or a variant of it for the F-35B is viable and that that engine design satisfies user improvement requests for the current engine.

A Pentagon decision on the future path for the F-35 engine may come this year (Defense Daily, Sept. 20).

Raytheon Technologies‘ [RTX] Pratt & Whitney F135 equips the Lockheed Martin [LMT] F-35 fighter, but the F-35 program has said that the fighter will need a new or significantly upgraded engine with improved electrical power and cooling capacity to accommodate the 53 new capabilities slated for F-35 Block 4.

Technology Refresh 3 (TR3)–spurred by the L3Harris [LHX] integrated core processor–is the computer backbone for Block 4, which is to have 88 unique features and to integrate 16 new weapons on the F-35.

Pratt & Whitney has said that its F135 Enhanced Engine Package (EEP) has “ample design margin” to allow for the envisioned Block 4 upgrades for the fighter and that EEP will save $40 billion in lifecycle costs.

GE has favored a new engine and said that it has tested out the second XA100 adaptive cycle engine at the Air Force’s Arnold Engineering Development Complex in Tullahoma, Tenn., for AETP (Defense Daily, Sept. 13).

The completion of the testing of the second XA100 comes a year after such testing on that engine began in August last year, General Electric said. The company has said that the XA100 would give the F-35 30 percent more range, more than a 20 percent increase in acceleration, and significant mission systems growth for Block 4.

Block 4 may cost $15 billion, while the Air Force has pegged the development cost of AETP for the F-35 at $6.7 billion –costs which the Air Force has not detailed Defense Daily, June 30).

“Part of the [future F-35 engine] conversation is what myself and [Air Force] Secretary [Frank] Kendall are a part of is we need to look at whatever the follow-on advanced propulsion is gonna be for the F-35, whether it’s AETP or EEP,” Air Force Chief of Staff Gen. Charles Q. Brown told reporters during the Air & Space Forces Association annual conference last week. “The other piece of this is actually doing the business case analysis, which is in OSD. We’d like to get to a decision this year to get to a point that we’d be able to say which way we’re gonna go, and then that way we could better invest and make sure we’re gonna provide opportunities in the future because there’s an aspect of the various variants of the F-35, which engine is gonna fit, is one thing to think through, and how do we do this, not just for the Air Force, or do we do this just for the Air Force, but also looking at the other services.”

It seems unclear whether AETP or EEP are the only options, or whether DoD may pursue an open strategy in which bidders may propose either a new engine or an upgraded one.

Since 2016, the Air Force has funded the AETP.