History of Flight
On 19 March 2009, a BAe 146-200 aircraft, registration ZS-PYM, operated a scheduled domestic flight from Cape Town International Aerodrome (FACT) to George Aerodrome (FAGG). The aircraft, with 4 aircrew and 57 passengers on board, departed FACT at 0507Z under instrument flight rules. After landing on runway 29 at FAGG at 0550Z, the flight crew experienced a number 1 engine flameout and a number 3 engine spooling down into a hung state. Line maintenance was carried out, and the aircraft was returned to service. For the return flight, the aircraft departed FAGG for FACT at 0727Z with 19 passengers on board.
During the approach to FACT, the captain observed that the thrust modulation system (TMS) for the number 2 engine was not functioning correctly. After landing on runway 19, with the throttles set to ground idle, all four engines spooled down and flamed out uncommanded. The auxiliary power unit provided electrical power, allowing the captain to steer the aircraft to taxiway Charlie. The passengers disembarked normally without incident.
Investigation Findings
Initial information indicated that the TMS was malfunctioning. Further investigation revealed that during base maintenance, the TMS had been deactivated. According to the manufacturer's maintenance manual, the aircraft maintenance organisation (AMO) was required to depower the system by pulling three primary circuit breakers. However, the AMO pulled a total of seven circuit breakers: three primary and four actuator centering circuit breakers. The manufacturer's manual warned that the four actuator centering circuit breakers should not be pulled. The result of pulling these four circuit breakers was that the actuators would not centre. Subsequently, during the approach and landing sequence, when the flight crew moved the throttles to ground idle, the actuators retracted and the power levers on the engine fuel controls moved below the ground idle position, causing the engines to spool down to sub-idle and flame out.
Probable Cause
Probable cause: All four engines spooled down and flamed out uncommanded.
Contributory remarks: The thrust modulation system (TMS) was malfunctioning. The AMO did not comply with the minimum equipment list (MEL 76-10-01) procedures when deactivating/reactivating the TMS. The AMO did not comply with the manufacturer's maintenance manual and other instructions for safe operation and continued airworthiness. The information that the four centering actuator circuit breakers had been pulled was not documented in any AMO maintenance documentation, and line stations were not aware of it.