Rolls-Royce is to modify the full-authority digital engine control (FADEC) software in the Bell Boeing V-22 tiltrotor after a FADEC failure resulted in an uncommanded take-off and hard landing during post-maintenance checks.
The cause of the failure is not yet known. The software improvement will speed up the automatic switching from a malfunctioning FADEC to its back-up to less than 1s.
In the 27 March incident, the crew of a US Marines Corps MV-22A was switching between FADECs during pre-flight checks after an engine change when the selected controller failed, causing a dramatic power increase to one engine. The control system reacted by increasing proprotor pitch to prevent an overspeed. This caused the aircraft to lift off rapidly to about 2m (6ft).
After 2-3s, the system detected the failure and switched to the good FADEC, which cut engine power to normal, causing a loss of lift and rapid descent. On impact, the right wing cracked at the root and the aircraft came to rest with its right nacelle resting on the ground.
For now, crews have been told to shut down the engines if a FADEC failure occurs on the ground or, once in the air, to increase proprotor pitch to maintain flight.
Source: Flight International