1998 Boeing 737-204 ADV G-SBEB Aft Cargo Door Fatigue Incident

Incident Overview and Flight Details On 13 August 1998 at 2120 UTC, a Boeing 737-204 ADV, registration G-SBEB, operated by an airline, was conducting a public transport flight between Ostend and Dover. The aircraft, manufactured in 1974 and powered by two Pratt & Whitney JT8D-15 turbofan engines, carried six crew members and 115 passengers. The incident resulted in one minor crew injury and four minor passenger injuries, with the primary damage identified as a cracked aft cargo door. ## Sequence of Events The flight departed London Gatwick Airport on schedule, arriving at Dubrovnik at 1807 UTC. The return flight was uneventful until the aircraft was in cruise at Flight Level 350. At 2100 UTC, air traffic control requested a descent to Flight Level 280. The first officer initiated the descent but noticed the cabin rate of climb indicator at the top of its scale. Attempts to control the rate via the standby system failed. The first officer donned his oxygen mask, while the commander, after checking the cabin altitude indicator reading 20,000 feet, lost consciousness while attempting to put on his own mask. ## Emergency Response and Landing The first officer initiated an emergency descent, transmitting a MAYDAY call to Maastricht ATC. After initial communication difficulties, he was cleared to descend to any level. In the cabin, passenger oxygen masks deployed automatically, and the senior cabin crew member manually deployed crew oxygen. She later collapsed near the flight deck door but recovered after receiving portable oxygen. The commander regained consciousness after the first officer successfully placed his oxygen mask on him. The aircraft descended to 8,000 feet before proceeding to Gatwick Airport, where it made an uneventful landing. Four passengers and the commander were taken to a local hospital for treatment. ## Engineering Investigation and Findings Ground pressurisation tests revealed the lower aft corner of the aft cargo door gaping open by about half an inch at a cabin pressure of 2 psi. Examination found a crack in the aft cargo door frame member at the aft/lower corner. Metallurgical analysis showed the crack initiated in fatigue at multiple sites in the inner radius of the outer flange-to-sidewall bend. The propagation mechanism changed from fatigue to fast tearing, extending to a total length of 12 inches. Additional cracks were found in the lower stop beam outer chord and web members. The crack surfaces at the origins in the chord fastener holes were contaminated with a polysulphide anti-fretting compound dissimilar to the manufacturer's type. ## Aircraft History and Maintenance At the time of the incident, the aircraft had accumulated 35,385 flight cycles and 86,446 flight hours. The cargo door had been subject to two related Service Bulletins. The first, SB 737-52-1065, related to FAA Airworthiness Directive 7626-02, required inspection and replacement of corner stop fittings. The lower fittings on this aft cargo door were replaced in September 1981, when the aircraft had flown approximately 12,000 flight cycles over 25,000 hours.