What happened
Approximately one hour after departure, while cruising at an altitude of 34,000 feet msl, a transport category airplane developed an electrical burning odor. The flight engineer observed smoke coming from the center console.
The aircraft completed an uneventful landing. Following the arrival, mechanics and FAA inspectors identified a hot lower incandescent lamp dimmer. The component remained hot enough to burn a mechanic nearly two hours after electrical power had been disconnected from the unit.
The investigation
Investigators removed and examined the dimmer and its associated circuit breakers. During this process, scorching was observed around the dimmer LV1 lead as well as on the lower side of both circuit breaker covers. The switch and the related circuit breakers were transported to the National Transportation Safety Board Materials Laboratory for further analysis; however, these items were lost during transit.