Open Cargo Door Sparks Global Maintenance Rules Change for Boeing 747-400 Freighters
A Boeing 747-400 freighter aircraft, registered G-ONEE, departed London Heathrow for Hong Kong on February 8, 2024. Shortly after takeoff, the crew encountered electrical system failures due to water ingress into the aircraft's electronics bay. The cause of the issue was a single event: the L1 cargo door had been left open during rain at Heathrow.
The investigation found that previous water ingress events on the 747-400 had produced service bulletins and airworthiness directives, but none required operators to check whether the protection systems were still working on a recurring basis. The UK Air Accidents Investigation Branch published its report on September 3, 2026.
The L1 door's failure led to water entering the cargo deck and pooling beneath the floor panels, where the Generator Control Units (GCUs) for buses 1 and 4 were located. The GCUs failed due to contamination from the water, causing both AC buses to isolate and removing power from various systems.
The crew managed the emergency situation by declaring a PAN to air traffic control and diverting to Amsterdam Schiphol Airport. Despite a subsequent flap issue during the approach, they landed safely without injuries or significant damage.