What happened
On April 15, 2010, a Beech B200GT, registration F-HSFA, was conducting a ferry flight from Melun Villaroche to Toulouse Blagnac. While cruising at flight level 230, the crew noticed that the cabin heating system was not providing the expected warmth in automatic mode. To rectify this, the crew switched the system to manual mode and adjusted the temperature.
Shortly after, a pungent smoke began to fill the cabin. The crew immediately donned oxygen masks, shut down the heating system, and declared an emergency. They initiated an emergency descent to flight level 100. While the smoke ceased during the descent, the crew maintained the emergency status and requested fire services for their arrival in Toulouse. The aircraft landed safely at 20:44 UTC.
The investigation
The investigation focused on identifying the source of the smoke within the aircraft's air conditioning and distribution system. Post-flight inspections revealed a split in a flexible hot air duct located beneath the cabin floor. The investigation found that an aluminum sheet and grey adhesive tape, used to wrap the duct, showed clear signs of overheating and melting.
Investigators examined maintenance records and found that the damage was not documented in any previous repair logs. The investigation established that during a recent maintenance check of the flapper valves, a mechanic had used a sharp tool to remove the thermal insulation. This action inadvertently sliced the duct. Furthermore, the technician had applied unauthorized adhesive tape to the area during reassembly, which later melted under the heat of the manual heating mode.
Findings
- The smoke was caused by the melting of adhesives on a damaged hot air duct.
- The duct was damaged by the use of a sharp tool during maintenance operations.
- The mechanic failed to follow the manufacturer's recommended functional test procedure, which would have avoided the need to disassemble the components.
- There was a lack of formalization regarding maintenance procedures and the use of adapted tools within the maintenance workshop.
- The technician's decision to use unauthorized adhesive tape was an individual initiative not supported by approved maintenance documentation.