Caused By Brief Power Interruption

A flight control system problem caused an F/A-22 Raptor to crash on the runway at Nellis Air Force Base, NV, on December 20th, according to an Air Force report released June 8th.

As ANN reported at the time, the pilot ejected and sustained minor injuries. The $133.3-million aircraft, assigned to the 422nd Test and Evaluation Squadron at Nellis, was destroyed when it crashed. Additional damage was limited to an arresting cable, runway guide sign, runway light and the runway itself.

The flight control system malfunction was caused by a brief power interruption to the aircraft’s three rate sensor assemblies, which caused them to fail. The assemblies measure angular acceleration in all three axes: pitch, roll and yaw. With three failed assemblies, the F/A-22 is not able to fly, investigators said.

When the pilot shut down engines for maintenance servicing, he left the auxiliary power unit running. Based on technical order guidance, he believed the power unit would supply continuous power to the flight control system. However, there was a less-than-one second power interruption to the assemblies during engine shutdown.

There is no automatic warning of this condition. To discover it, the pilot would have had performed a diagnostic test. The pilot accomplished a successful test before engine shutdown, and because the power unit was on, he believed a second test was unnecessary.

FMI: www.af.mil