What happened
On 30 September 1998, a Lockheed L1011 Tristar, registration TF-ABT, was operating a charter flight from London Gatwick to Venice. During the initial climb through approximately 80 feet, the crew experienced a loud bang, a leftward yaw, and a nose-down trim change. The flight crew immediately identified a failure in the No 1 engine, which was accompanied by severe vibrations.
While performing the engine shutdown procedure, the flight engineer noticed an 'AREA A OVERHEAT' warning on the engine bleed control panel. To mitigate the issue, the crew deactivated the No 1 air conditioning pack. Despite the shutdown, the engine continued to produce an unusual rattling noise. The commander subsequently declared an emergency, jettisoned approximately 15,000 lb of fuel, and returned to Gatwick for a two-engine approach and landing. There were no fatalities and no injuries among the 14 crew members or 289 passengers.
The investigation
The investigation focused on the structural damage to the aircraft and the mechanical failure of the engine. Post-flight inspections revealed that a panel near the nose landing gear was missing. Detailed examination of the aircraft showed that the hinged left-side door to the Environmental Control System (ECS) bay had been torn from its hinges. The force of the internal pressure had even pushed the latching shoot bolts past their striker plates.
Investigators found that the missing ECS bay door had been ingested by the No 1 engine, resulting in severe damage to the fan blades and the engine nacelle. Fragments of the door had also penetrated the bypass duct, causing damage to the duct lining. The investigation traced the sequence of events back to a failure in a pneumatic duct located near the bulkhead separating the ECS bay from the forward freight hold.
Findings
- The primary cause of the incident was the failure of a titanium pneumatic duct due to fatigue.
- The duct failure caused a rapid increase in pressure within the ECS bay, which exceeded the capacity of the pressure relief blow-out door.
- This internal pressure forced the ECS bay door to detach from its hinges and enter the path of the No 1 engine.
- Hardness testing revealed that the weld area of the failed duct was significantly harder than the surrounding material, suggesting weld embrittlement caused by gas contamination during manufacturing.
- Fatigue damage was found to have compromised approximately 80% of the wall thickness at the fracture site.