What happened
On 19 February 2001, a Boeing 757-28A, registration G-OOOB, was performing a scheduled public transport flight from Las Palmas to Glasgow. While taxiing for departure, passengers and cabin crew in the rear galley heard a loud bang. Although the flight crew did not hear the noise, they noted a minor change in cabin pressure, though no flight deck instruments indicated any abnormalities.
Following a consultation with the cabin crew, the commander decided to return to the stand. During the shutdown procedures at the remote stand, reports of smoke in the rear of the aircraft were received. Due to the lack of airstairs at the remote location, the commander initiated an emergency evacuation using the aircraft's escape slides. All 232 passengers and 9 crew members evacuated the aircraft without no injuries.
The investigation
Investigators determined that the incident was triggered by the rupture of an Auxiliary Power Unit (APU) bleed air duct at a welded joint. This specific duct, part number 212N3076-9, is responsible for transporting pressurized air from the APU compressor to the air conditioning packs while the aircraft is on the ground. The failure occurred near the forward bulkhead of the aft cargo compartment, behind insulation and liner panels.
While smoke was reported in the cabin, the investigation found no evidence of an actual fire. Instead, the smoke was likely composed of dust and insulation material that was dispersed into the passenger cabin following the duct's rupture. The failed component had been in service since the aircraft's manufacture in 1987, accumulating over 60,000 hours and 20,000 cycles.
Findings
- The primary cause of the event was the rupture of an APU bleed air duct at a welded joint.
- The reported smoke was likely airborne insulation and dust rather than combustion products.
- A design change had been implemented by the manufacturer in 1989 to improve duct durability (transitioning to part number 212N3076-10), but this was a production change only and was not retrofitted to older aircraft via a Service Bulletin.
- Inspections of the operator's remaining fleet revealed that two other ducts of the same part number also exhibited cracks, suggesting a systemic fatigue issue in the older design.