What happened
On September 20, 2011, a Fokker F27 MK500, registration I-MLHT, departed Paris Charles de Gaulle for Dôle Tavaux as a scheduled cargo flight. During the initial climb, while approaching flight level 60, the crew observed an engine fire warning and an audible alarm for the right engine. The crew immediately implemented engine fire procedures, utilized one of the two available fire extinguishers, and shut down the right engine. After the fire warning light extinguished, the crew performed a turn-back and executed an emergency landing on runway 27L at Paris Charles de Gaulle without further incident.
The investigation
The BEA investigation focused on the right engine, a Rolls-Royce Dart RDa7 mark 532-7. A visual inspection revealed significant heat damage on the engine cowling and a perforation in combustion chamber No. 4. Technical analysis of the engine revealed that a small component—a ferrule (part number PNKB5281) from the engine fire extinguishing circuit—was lodged in the fresh air supply chamber near the fuel injector.
Investigators determined that during a recent maintenance task on September 16, 2011, a technician had replaced combustion chamber No. 3. To facilitate this, the technician also disconnected the "three-way junction" of the fire extinguishing circuit. During this process, the ferrule likely fell into the compressor's air stream and settled in a low point of the compressor casing. Upon engine startup, the airflow pushed the ferrule into the combustion chamber, where it became lodged against the fuel injector.
Findings
- The presence of the ferrule in the airflow path created a turbulent, low-pressure zone around the flame tube.
- This turbulence caused abnormal heating, which led to the perforation of the flame tube, the outer air casing, and the anti-burst strap.
- The escaping hot gases triggered the engine fire detection system.
- The maintenance documentation (Rolls-Royce Maintenance Manual) lacked specific details for replacing a single combustion chamber while the engine is installed on the aircraft.
- The operator's work card did not include specific instructions for the three-way junction or its associated ferrules.
- The Illustrated Parts Catalogue (IPC) failed to reference the ferrule located on the cold side of the junction, preventing the technician from noticing its absence during reassembly.