What happened
On October 4, 2018, a Dassault Aviation Falcon 2000EX, registration HB-IAU, departed Zurich Airport (LSZH) for Paris le Bourget. Approximately two minutes into the climb at flight level 70, the crew heard a loud bang and experienced a failure of the right engine. This engine failure caused the loss of the right generator, which subsequently led to the failure of the autopilot, the pitch trim, and one of the two radio systems.
The flight crew requested immediate radar vectors to return to Zurich. During the return, the crew initially indicated they were not ready for an instrument approach, but later declared a "Mayday" and eventually signaled readiness for landing. During the approach to runway 14, the aircraft drifted east of the localizer due to an autopilot mode change triggered by a brief signal disturbance. The crew eventually stabilized the aircraft and landed safely at Zurich.
The investigation
Investigators examined the engine's electronic control data, which showed no internal engine malfunctions. However, a physical inspection revealed that the emergency fuel shut-off valve had closed, cutting off the fuel supply. This valve is designed to close only in the event of a low-pressure turbine shaft break.
The investigation found that the engine had been reinstalled just two days prior following repairs. While the valve's adjustment had been checked after installation, subsequent checks revealed that the adjustment was out of tolerance. Further technical scrutiny revealed that the Bowden cable leading to the valve was stiff and moved jerkily, and the return spring force within the valve had decreased. Both components were subsequently replaced.
Findings
- The right engine failed because the emergency fuel shut-off valve triggered due to incorrect adjustment.
- The loss of the right generator caused the simultaneous failure of the autopilot, pitch trim, and one radio.
- The aircraft's deviation from the localizer course during the approach was caused by a temporary signal disturbance that altered the autopilot programming.
- The crew's failure to monitor flight instruments effectively during the turn was likely exacerbated by self-imposed time pressure during the emergency return.