What happened
On July 28, 2013, an Air France Boeing 777-300, registration F-GSQA, was parked at Paris Charles de Gaulle preparing for a flight to Shanghai. During the boarding process, the flight crew activated the Auxiliary Power Unit (APU) to provide cabin air conditioning.
At approximately 22:54, the flight crew detected a burning odor. As the crew investigated, smoke began to spread through the cabin. An onboard alarm (SMOKE REST UPPER DOOR 1) alerted the cockpit to smoke detection near the crew rest area. The smoke eventually became thick enough to enter the cockpit, prompting the co-pilot to shut down the two air conditioning packs.
Following the detection of smoke appearing to originate from the APU, the captain ordered an evacuation. While the captain intended for a rapid deplaning via the boarding bridges, the cabin crew at doors 3G/3D interpreted the instructions as a full emergency evacuation and deployed the slides. During the evacuation, one passenger sustained a serious injury (a fractured elbow).
The investigation
The BEA examined the APU, the aircraft's air conditioning systems, and the crew's response. Technical analysis of the APU, conducted in collaboration with Honeywell, focused on the ventilation circuit. The investigation also reviewed the toxicity of the smoke, noting that the Mobil Jet Oil II used in the APU can release neurotoxic compounds like Tri-Cresyl-Phosphates (TCP) when heated through pyrolysis.
Findings
- The smoke in the cabin and cockpit was caused by the pyrolysis of oil within the APU ventilation system.
- A failure of an APU ball bearing led to an axial movement of the compressor module, which damaged a carbon seal and allowed lubricating oil to leak into the compressor.
- The use of imprecise terminology by the captain regarding the evacuation method contributed to the crew's misunderstanding.
- The lack of a specific airline procedure for "rapid deplaning" (as opposed to a full emergency evacuation) led the cabin crew at doors 3G/3D to deploy the emergency slides.
- The crew's decision to leave the cockpit to investigate the odor prevented the captain from having a complete real-time overview of the cabin situation.
Safety action
Air France implemented several corrective actions, including:
- Developing a "precautionary deplaning" procedure.
- Improving the use of respiratory protection during persistent odor events.
- Enhancing crew training on intercommunication methods.
- Studying the risks associated with the toxicity of fumes from lubricating oils.