The complex simulations at Naval Air Station Patuxent River in Maryland were meant to test how well the F-35 would perform in real-world combat scenarios.
With more than 80% of the Air Force's energy going to power aircraft, making planes more fuel-efficient is a major part of the department's climate plan.
If the testing process were to slip further, "there's not a lot of leeway" to reach a decision on full-rate production by the end of fiscal 2023, Lt. Gen. Eric Fick said.