What happened
On 8 March 1998, a McDonnell Douglas DC-10-30, registration N68065, was preparing for a scheduled passenger flight from Manchester to Newark, USA. During taxiing at Manchester Airport, the flight crew noticed a strange odour in the cabin, which they suspected was gasoline. While the aircraft was proceeding toward the runway, ground controllers and the tower observed vapour emanating from the No 2 engine.
As the aircraft continued its taxi, the vapour developed into a visible fuel leak, and a fire subsequently ignited in the No 2 engine. The commander immediately halted the aircraft and requested the Airport Fire Service. Upon the arrival of fire crews, the fire intensified, prompting the commander to initiate an emergency evacuation. The evacuation of the 249 passengers and 14 crew members was completed, though 2 minor injuries were reported.
During the evacuation, several issues occurred with the emergency slides. At the left overwing exit (door 3L), the first section of the slide inflated, but the second section failed to reach the ground, leaving passengers stranded on the wing. Additionally, the slide at the forward right door (1R) failed to achieve full inflation pressure, resulting in a steep, unstable angle that required firefighters to physically hold the slide in place to allow passenger use.
The investigation
The AAIB investigation focused on the mechanical cause of the engine fire and the failure of the emergency equipment. Investigators examined the fuel-cooled oil cooler (FCOC) from the No 2 engine and performed a metallurgical analysis of its components. The investigation also included a review of the emergency slides, involving coordination with the NTSB and the slide manufacturer.
Regarding the slides, investigators found that the overwing slide (3L) showed no obvious mechanical defect that would explain the failure to inflate automatically. However, they noted a disconnected manual inflation cable, though this was not believed to be the cause of the failure. For the forward right slide (1R), investigators identified internal damage to the regulator valve, specifically a regulating spring that had become coil bound due to abnormal vibration, which likely caused the low inflation pressure.
Findings
- The fire was caused by an internal failure of the fuel-cooled oil cooler (FCOC) in the No 2 engine.
- A rupture in a fuel matrix tube allowed pressurized fuel to enter the engine's lubrication system.
- This leakage allowed fuel vapours to enter the oil vent system, where they ignited in the jet pipe.
- The rupture was caused by fatigue cracks in the unit's divider plate, which led to the thinning and eventual failure of the tube walls due to fretting.
- The failure of the 1R slide was attributed to internal damage within the regulator valve caused by vibration.