What happened
On 18 October 1999, a Boeing 767-336, registration G-BNWM, was performing a passenger flight from Gatwick Airport when the aircraft experienced a significant engine malfunction shortly after takeoff. While climbing to approximately 450 feet, the crew heard a loud bang followed by a rapid reduction in power from the No 2 engine. This event was accompanied by intense vibrations, and several passengers observed flames emitting from the right-hand engine.
Prior to the incident, the flight crew had observed a flock of birds passing beneath the aircraft. Suspecting a birdstrike, the pilots shut down the No 2 engine. The commander subsequently initiated an immediate return to Gatwick, performing an overweight landing that concluded without further incident. There were no fatalities and no injuries among the 11 crew members or 129 passengers on board.
The investigation
Investigators examined the No 2 engine and discovered that one fan blade had fractured, with the outer nine inches of the blade becoming embedded in the acoustic lining of the fan duct. The inspection revealed that the fan blades adjacent to the fracture showed impact damage consistent with a soft body strike, including curled tips. Additionally, the fan tip-path abradable lining had been heavily gouged, and a segment of this lining was missing.
Analysis of the biological remains identified the striking object as a wood pigeon. Metallurgical testing of the fractured blade parts showed no evidence of pre-existing cracks or material defects that would have made the blade susceptible to failure.
Findings
- The engine strike involved a wood pigeon, a species capable of weighing up to 740 grams.
- While the engine type is certified to withstand the ingestion of birds weighing up to 1.5 lbs, the damage sustained was more severe than expected for a bird of this size.
- A critical factor in the failure was the detachment of a segment of the abradable liner, which had been previously repaired.
- It is believed that this detached segment of the liner acted as a ramp, driving the fan blade tips against the adjacent liner and inducing the stresses that led to the blade fracture.