What happened
On 20 March 2001, a DHC-8-311, registration G-JEDD, was performing a scheduled public transport flight at Bristol International Airport. The aircraft, operated by a company conducting line training, had been parked at the terminal during a period of deteriorating weather characterized by heavy snow and freezing temperatures. During the turnaround, the crew did not install engine intake blanking plugs.
After the aircraft was de-iced and the crew completed a pre-flight inspection, the aircraft began taxiing for departure. While holding at the runway 09 threshold, the right engine suddenly lost power. As the crew followed the engine failure procedures, the left engine failed approximately two minutes later. The aircraft was left without engine power on the taxiway, necessitating the use of a tug to return to the ramp and a bus to disembark the 25 passengers and 4 passengers crew.
The investigation
Investigators examined the engine nacelles and found that while a visual inspection of the intake lips had appeared clear, a more detailed inspection using a ladder and torch revealed significant accumulations of wet slush deep within the bypass plenum. This buildup was present in both engines.
Analysis of the flight recorders showed that the right engine's power, torque, and fuel flow dropped simultaneously during the event. The investigation also noted that during the engine failure checklist, the crew did not select the ignition to the manual 'ON' position for the remaining operational engine. Furthermore, it was determined that the aircraft lacked a specific modification—an auto-relight system—that could have automatically triggered the igniters during a transient power loss.
Findings
- The primary cause of the dual engine failure was the sudden ingestion of wet snow and slush that had accumulated inside the engine intake bypass plenum while the aircraft was parked.
- The accumulation was located deep enough within the nacelle that it was not detectable through a standard visual or tactile inspection from the ground.
- The failure of the second engine was exacerbated because the ignition on the left engine was not set to manual, which would have provided continuous spark to prevent a flameout during airflow disturbances.
- The aircraft was not equipped with the optional auto-relight system modification, which would have provided automatic protection against such transient power interruptions.