Incident Overview
Shortly after takeoff, while climbing through 500-600 feet above ground level, the flight crew detected smoke in the cabin. They declared an emergency and immediately returned to the departure airport, landing without further incident. After the aircraft came to a stop, crash fire rescue personnel extinguished a fire that had developed in the overhead paneling of a coat closet located directly behind the cockpit.
Examination Findings
Post-incident examination of the aircraft revealed extensive heat damage to the overhead paneling around a closet light fixture in the cabin. Visual inspection of the damaged area showed that electrical wiring and an oxygen line were installed in close proximity to each other near the light fixture. Examination of the oxygen line uncovered a pin-size hole through its circumference, with damage signatures consistent with electrical arcing. Further analysis of the light fixture identified areas of severe localized heating and melting.
Maintenance History
Review of the aircraft's maintenance records disclosed two entries within the previous 12 months describing that the closet light circuit breaker had popped during illumination of the light. Both instances were attributed to electrical arcing between the light assembly and the oxygen line. The corrective action in each case involved installing Teflon tape to protect against interference between the assembly and the oxygen line.
Conclusion
No other causal factors were identified beyond the arcing event between the light fixture and oxygen line, with prior maintenance attempts failing to eliminate the underlying interference.