What happened
On 13 November 2014, a Beechcraft 300 Super King Air, registration SE-KOL, was prepared for a ferry flight intended to return the aircraft to Sweden. During the engine start sequence at Farnborough Airport, the crew noticed an electrical odour within the cabin. Upon investigation, the co-pilot identified smoke emerging from beneath the floor, specifically in the area aft of the main wing spar.
As the smoke density increased and began to obstruct visibility, the commander declared an emergency and initiated an immediate evacuation of the aircraft. Emergency services arrived at the scene and utilized infra-red equipment to locate a heat source beneath the floorboards, confirming the presence of an active thermal issue.
The investigation
Investigators determined that the source of the smoke and heat was the electrical flap motor. The investigation established that the flaps had overtravelled their intended position, pressing firmly against the mechanical up stop. This continuous engagement caused the motor to overheat significantly. The overheating continued until the electrical circuit breaker eventually tripped, halting the current.
Following the incident, maintenance work was performed to replace the motor, the limit switch, and the flap control relay. The flap system was also re-rigged. However, the investigation could not determine which specific component failure or mechanical issue caused the flaps to overtravel.
Findings
- The primary cause of the smoke and heat was the overheating of the electrical flap motor.
- The motor overheated because the flaps had moved past their intended limit and were held against the mechanical up stop.
- The electrical circuit breaker eventually tripped, which stopped the overheating process.