Accident Overview
On 20 January 2007 at 1651 UTC, a Dassault-Breguet Mystère-Falcon 900B, registration G-HMEV, experienced a failure of its No. 3 engine while climbing through FL130 approximately 7 nm south-west of Worthing, Sussex. The aircraft, operating a commercial air transport flight from Farnborough to Tel Aviv, had two crew and no passengers on board. No injuries were reported.
Flight History
The aircraft departed Farnborough at 1640 UTC. About 10 minutes later, while at FL130, the crew heard a loud noise from the rear. Shortly after, an engine fire aural warning activated and the No. 3 Engine fire warning light illuminated. The pilots observed fluctuating ITT indications and executed the engine fire procedure, shutting down the engine and firing the extinguisher. The fire warning ceased. The crew declared a mayday to London Terminal Control and were vectored to Gatwick Airport, which they accepted due to its fully equipped rescue and firefighting services and adequate runway length. Approximately two minutes after the mayday, the fire was declared under control. The diversion was uneventful, though multiple GPWS 'too low, flaps' callouts occurred during the approach. The aircraft landed 12 minutes after the event. The operator initially intended to ferry the aircraft to Farnborough on the remaining engines, but after AAIB inspection, no further flights were conducted until repairs.
Engine Examination
Examination revealed major disruption of the low-pressure (LP) turbine assembly in the No. 3 engine (Honeywell TFE731-5BR-1C). Debris from the turbine assembly ruptured the engine casing, holed the nacelle cowl, and caused slight damage to the horizontal stabiliser. Many fractured parts were lost overboard. The LP turbine comprises three stages; the Stage 2 turbine has 52 blades. One Stage 2 blade showed signs of a casting defect, and fracturing of this blade likely initiated the turbine assembly break-up. However, there had been previous cases of Stage 3 blade fracture, which could also have caused the damage. The turbine casing had ruptured in prior blade failure incidents, but not where a newer standard casing was fitted. The engine manufacturer issued Service Bulletins in late 2007 recommending replacement with the later standard casing, though this modification was not mandated.
Probable Cause
The failure had probably resulted from the fracturing of an LP turbine blade, possibly due to a casting defect in a Stage 2 blade or fracture of a Stage 3 blade, leading to non-contained turbine assembly disruption.
Safety Recommendations
Two Safety Recommendations have been made by the AAIB. Additionally, the investigation noted that the flight data recorder (FDR) model (L-3 Communications F800) used magnetic tape and suffered data errors; solid-state recorders are less susceptible to such vibration-induced errors. The ICAO Flight Recorder Panel is reviewing the suitability of magnetic tape recorders.