What happened
On 28 December 2005, a Boeing 747-436, registration G-CIVY, was operating a passenger flight from New York JFK to London Heathrow. During the flight, the crew noted a 'burnt bird' smell following a previous engine bird strike, but no immediate concern was raised. However, while over the Irish Sea near Strumble Head, Wales, the cabin crew reported a smell of burning and a visible haze originating in the first-class galley and spreading through the lower deck.
As the aircraft began its descent, the flight crew observed a 'NUMBER 3 GALLEY BUS' alert on the secondary Engine Indicating and Crew Alerting System (EICAS). Simultaneously, cabin crew reported loud metallic noises, described as 'graunching and banging,' coming from beneath the floor. The commander declared a MAYDAY and diverted the aircraft to Cardiff. As a precaution, the flight crew donned oxygen masks, and cabin crew prepared for a potential emergency evacuation.
The investigation
The investigation examined the cause of the smoke, the electrical alerts, and the mechanical noises reported by the crew. While the cabin crew perceived the smell as electrical, the flight crew did not experience similar symptoms on the flight deck, likely because the cockpit receives less recirculated air than the cabin.
To address the mechanical noises, the commander isolated the No 2 Air Cycle Machine (ACM). The investigation also looked into the electrical bus failure and the source of the haze. Maintenance inspections following the event included a borescope of the engines and a thorough check of the galley wiring.
Findings
- The primary cause of the smoke and haze was food debris found in the galley ovens.
- The mechanical noises reported by the cabin crew were linked to the No 2 ACM, which was removed and replaced.
- No defects were found in the galley wiring that could have caused the circuit breakers to trip.
- The aircraft returned to service after the ovens were cleaned and the ACM was replaced.