What happened
On 3 September 2014, a Boeing 737-36Q, registration G-GDFT, was operating a passenger flight from Ibiza to East Midlands Airport. During the descent, the flight crew noticed a series of simultaneous system failures, including the loss of the PA system, weather radar, and engine fuel flow indications. The crew identified the issue as a failure of the battery busbar and requested an expedited approach.
During the approach, the crew encountered further complications when landing gear indications disappeared. After a period of flying above the runway to visually confirm the gear's position, the aircraft landed safely. However, as the aircraft taxied toward its parking stand, an acrid smoke haze appeared in the cabin and flight deck. The crew declared a MAYDAY and initiated an emergency evacuation. While the evacuation was successful, the crew faced challenges due to a non-functional PA system and a faulty loud hailer. One passenger sustained a minor injury.
The investigation
The AAIB investigation focused on the electrical failure and the subsequent appearance of smoke. Engineers discovered that the electrical symptoms could be reproduced by applying ground power, confirming a loss of continuity in the electrical system. Further examination of the R1 relay revealed that several terminals had become loose and detached from their insulated mountings. The investigation also looked into the source of the smoke, finding that the loss of the battery bus caused the air cycle machine (ACM) cooling fans to stop. This led to the overheating of the ACM, causing dust and oil residue on the hot metal ducts to burn off, creating the smoke haze.
Additionally, the investigation examined the emergency equipment. The 1R escape slide had twisted during deployment, rendering it unusable, though no mechanical fault was found with the slide itself. The forward emergency loud hailer was found to be missing its volume control knob and was set to minimum volume.