What happened
On 11 January 2006, an Avro 146-RJ100, registration G-CFAE, was prepared for a scheduled passenger flight from Edinburgh to London. Because the aircraft's Auxiliary Power Unit (APU) was unserviceable, the crew was operating on ground power. During the engine start sequence, the crew attempted to start engine No 4. However, the required procedure to increase the engine N2 speed to 65% before starting the subsequent engine was not followed.
As the crew initiated the start for engine No 3, the increased load on the operating generator caused the engine to drop into a sub-idle condition. This resulted in over-fuelling and a subsequent jet-pipe fire on engine No 4. A ground handler alerted the flight crew to the flames. Simultaneously, the electrical load caused the generator to trip, leaving the aircraft running solely on battery power.
While the pilots focused on fire suppression, the cabin crew became isolated. The loss of AC power rendered the remote cockpit door release inoperative, and the locked door prevented the purser from communicating with the pilots. Seeing the fire, the cabin crew initiated an emergency evacuation. All 98 passengers and 5 crew members successfully exited the aircraft via the front left slide before the fire service arrived.
The investigation
The AAIB examined the engine start procedures, the functionality of the internal communications system under degraded power, and the impact of the locked cockpit door policy. The investigation reviewed flight data recorder (FDR) and cockpit voice recorder (CVR) data, which confirmed that the engine N2 speed had not reached the necessary threshold before the next start was attempted. The investigation also looked into the limitations of the interphone and PA systems when operating on battery power and the inability of the cabin crew to access the flight deck.
Findings
- The primary cause of the engine fire was the failure to increase the N2 speed of the operating engine to 65% as required when the APU is unavailable.
- The loss of AC electrical power severely restricted the functionality of the aircraft's internal communications, preventing the purser from contacting the flight deck.
- The locked cockpit door prevented the cabin crew from establishing liaison with the pilots during the emergency.
- The cabin crew lacked sufficient training regarding the specific limitations of the communication systems during degraded electrical conditions.