Incident Overview
On final approach, the flight crew turned the aircraft's cabin environmental control system from the automatic mode to the off position. Shortly thereafter, the cockpit and cabin began to fill with smoke. The occupant of the copilot's seat reported feeling heat around his feet. The crew executed a normal landing, and all passengers and crew exited the aircraft without injury.
Examination Findings
Post-incident examination revealed that the fiberglass ducting located on top of the heater plenum chamber had caught fire. The fire burned a hole through the pressure bulkhead and into the avionics compartment.
Operational Context
The crew's action of switching the environmental control to off occurred while the aircraft was on final approach. No further details regarding the specific aircraft type, registration, operator, or location were provided in the investigation source. No injuries were reported among the occupants.
Conclusion
The source does not state a probable cause for the incident.