What happened
On 2 June 2016, an F-16CJ, tail number 92-3890, was destroyed following a ground impact near Peterson Air Force Base, Colorado. The aircraft, operated by the 57th Wing of the United States Air Force Air Demonstration Squadron (USAFADS), was performing a six-aircraft flyby and airshow sequence for a United States Air Force Academy graduation ceremony in Colorado Springs.
During the landing pattern, while positioned on the downwind leg, the pilot inadvertently moved the throttle to the engine cutoff position. This action occurred below the minimum altitude and airspeed required to attempt an engine restart or perform a flame-out landing. The pilot was forced to eject over a grassy area in El Paso County; the pilot sustained one minor injury, while no other personnel were harmed.
The investigation
The investigation focused on how the throttle reached the cutoff position, a state that normally requires the physical actuation of the throttle cutoff release trigger. Analysis by the Air Force Research Laboratory/Materials Integrity Branch revealed that the throttle trigger was intermittently sticking and binding.
Investigators found that the throttle trigger bushing had suffered damage and wear due to a misalignment of the clevis pin. This misalignment, combined with metallic-particle debris contamination and the use of an unauthorized lubricant in the assembly, increased the likelihood of the trigger remaining in a retracted, stuck position. This malfunction effectively bypassed the safety mechanism intended to prevent the throttle grip from being rotated outboard into the cutoff zone.
Findings
- The primary cause was the actuation and subsequent malfunction of the throttle trigger, which remained stuck in the retracted position.
- The pilot inadvertently rotated the throttle grip fully outboard while retarding the throttle toward the idle position.
- Maintenance Technical Orders lacked sufficient detail to consistently identify clevis pin misalignment or a sticking throttle trigger.
- Debris contamination and improper lubrication exacerbated the mechanical binding of the trigger assembly.