Incident Summary
Following departure, the flight crew observed smoke emanating from the cabin. In response, they initiated a return to the departure airport and executed a safe landing.
Investigation Findings
Post-incident examination revealed that a bearing within the forward cabin ventilation blower motor had failed. Subsequent to the bearing failure, the wires and resistors associated with the ventilation motor overheated. Evidence of charring and soot was present on the blower motor housing. The resistors, which facilitate low-speed fan operation, exhibited indications of thermal damage.
The electrical system incorporated current limiters intended to safeguard the circuit. However, further analysis determined that the wiring and resistors were not sufficiently protected when the fan operated in low-speed mode.