Failure In F-16 Engine ‘Blind Spot’ Caused Crash, Report Says

Fan blade failure in a known “blind spot” of F-16 engine maintenance caused a Fighting Falcon to crash in New Mexico in 2024, a U.S. Air Force report says, prompting new questions on if inspection procedures should change for the aging fighter.

The Block 42 F-16C, assigned to Holloman AFB, New Mexico, crashed shortly after taking off on April 30, 2024. The pilot was able to eject safely, and the aircraft was destroyed at a loss of $21.7 million.

An Air Force Accident Investigation Board (AIB) report into the incident, released Feb. 5, says the cause was a misaligned or turned No. 10 position variable stator vane in the fifth stage of the aircraft’s Pratt & Whitney F100-PW-220 engine. This triggered a subsequent breaking free of a fifth-stage compressor blade, causing catastrophic engine damage.

The engine damage happened about 1 min., 18 sec. after takeoff, at 1,030 ft. above ground level and 329 kt. calibrated air speed during a slightly climbing turn. It caused an unrecoverable stall and the pilot’s “only possible favorable outcome was ejecting before running out of altitude or airspeed,” the report says.

The AIB report outlines a unique maintenance issue facing the PW100-220. The aircraft, which was previously based at Luke AFB, Arizona, experienced a foreign object debris (FOD) incident that caused damage to blades in the engine’s first stage in 2022. Following procedure, 15 first stage blades were repaired and inspected and all “accessible stages of the engine were inspected.” Inspectors found no damage in the second through fourth stages, nor in the sixth through 13th stages.

The engine’s fifth stage is not inspected, other than in a depot-level maintenance teardown of the engine core and high-pressure compressor. Therefore, investigators could not be sure if damage from the FOD incident contributed to the misaligned or turned variable stator vane in this fifth stage.

Investigators also said it is possible, though not likely, that a single vane could be incorrectly assembled at the depot and then missed during a quality assurance inspection. Interviewed professionals said a misaligned vane would cause a whole set to bind and not pass inspection.

“Furthermore, it is unlikely the engine would perform most of its calculated cycles before the next scheduled depot overhaul without incident if the vane were incorrectly assembled during the previous overhaul,” the report says. “While historical instances suggest the possibility of a vane being turned by maintenance activity, I found no evidence of improper maintenance activity.”

Going forward, it is an open question if these maintenance procedures should change, the report says. In a section on contributing factors to the mishap, the AIB president writes that this known “blind spot” of not inspecting when field procedures do not indicate damage will require a deliberate risk assessment by the F-16’s system program office.

“The risk assessment is based on the historical and anticipated probability of damage before scheduled maintenance compared to the severity of possible adverse effects,” the report says. “This deliberate risk assessment is informed by the limited time, manpower, and funding available to pull an engine out of an aircraft in the field, ship it to depot-level maintenance, perform a teardown, inspect it and make repairs (if any), reassemble it, ship it back to the field, and reinstall it into an aircraft.”

Performing this unprescribed, unscheduled maintenance even out of an abundance of caution would adversely impact the whole program and other programs that compete for resources, the report says.

“However, it is highly likely this specific mishap might have been avoided if post-FOD event policy or general life cycle procedures prescribed a shorter deadline for the next depot-level scheduled maintenance,” the report says.