What happened
On 14 March 2000, a BAe RJ85, registration OO-DJS, was performing a scheduled public transport flight from London City Airport to Brussels. The flight departed from Runway 28 under clear weather conditions. During the initial climb to 3,000 feet, the flight crew noticed a brief period of vibration. Shortly thereafter, the vibration intensified significantly, accompanied by a low oil pressure warning and a fire warning for the No. 3 engine.
Passengers and cabin crew reported seeing flames emanating from the inboard right engine nacelle. The flight crew immediately initiated the engine fire drill, successfully discharging both fire bottles to extinguish the flames. A 'MAYDAY' was declared, and the crew requested an immediate return to London City Airport. The aircraft completed an ILS approach and landed safely on the remaining three engines. There were no injuries to the 55 passengers or 4 crew members on board.
The investigation
The AAIB investigation focused on the mechanical failure of the No. 3 engine. Flight data recorder analysis revealed that while engine parameters were normal during takeoff, vibration levels spiked rapidly 90 seconds into the flight, followed by the fire warning.
Detailed examination of the engine by the manufacturer revealed that the high pressure rotor shaft had seized. The No. 2 bearing assembly and air diffuser had sustained severe heat damage. Investigators determined that the fire originated from an internal oil fire within the bearing cavity. This intense heat caused a brazed joint on the No 2 bearing oil scavenge tube to melt, which allowed the fire to escape the engine interior and spread into the nacelle.
Findings
- The primary cause of the engine fire was the failure of the No. 2 bearing, which led to frictional heat and the ignition of engine oil.
- It is believed that air leakage past the bearing carbon seals may have pressurized the bearing cavity, restricting the necessary oil flow and causing the bearing to overheat.
- The fire spread to the engine nacelle because the brazed joint on the oil scavenge tube failed due to the heat of the internal fire.
- The nature of this specific bearing failure was not detectable through standard engine health monitoring or existing maintenance protocols.
Safety action
- Recommendation 2001-61: The engine manufacturer should ensure the modified oil pump, designed to maintain oil supply even if the bearing cavity is pressurized, is installed on all affected engines.
- Recommendation 2001-62: The engine manufacturer should ensure that scavenge tubes with welded joints, rather than brazed joints, are installed on all affected engines to prevent fire from spreading to the nacelle.