LAX01IA073

The transport category airplane developed an electrical burning odor about 1 hour after departure while at an altitude of 34,000 feet msl. The flight engineer noted smoke emanating from the center console. Following an uneventful landing, mechanics and FAA inspectors found a hot lower incandescent lamp dimmer, which burned the mechanic nearly 2 hours after electrical power was removed from the component. The dimmer and its corresponding circuit breakers were removed and examined. Scorching was noted around the dimmer LV1 lead and on the lower side of both circuit breaker covers. The switch and related circuit breakers were sent to the National Transportation Safety Board Materials Laboratory for examination, but were lost in transit.

On January 5, 2001, approximately 1410 Hawaiian standard time, a Boeing 747-200F transport category airplane, N470EV, experienced smoke in the cockpit en route from Honolulu, Hawaii, to Pago Pago, American Samoa. The pilot declared an emergency and landed uneventfully in Honolulu. The airplane was not damaged and there were no injuries to the airline transport rated pilot, co-pilot, and flight engineer. The airplane was operated by Evergreen International Airlines, Inc., McMinnville, Oregon, as a regularly scheduled cargo flight under the provisions of 14 CFR Part 121. An instrument flight plan was filed for the flight.

According to the operator, the flight was approximately 1 hour out of Honolulu at a flight level of 34,000 feet msl, when the flight crew detected the odor of burning insulation. The flight engineer examined the main cargo deck and aft upper deck and found no anomalies. Upon his return to the cockpit, the flight engineer noticed smoke coming from the aft right corner of the center pedestal. The flight crew performed the electrical fire/smoke checklist and the smoke dissipated.

After the airplane returned to Honolulu (at 1512), maintenance personnel and Federal Aviation Administration (FAA) inspectors examined the center console area. While troubleshooting the wiring in the center console, one of the mechanics burned himself on the lower incandescent lamp dimmer (Boeing part number 60B40024-3). The FAA inspectors reported the case was still hot after having power removed for over 2 hours. Neither circuit breaker attached to the dimmer had opened. When the mechanic manually opened the circuit breakers, they were so hot the mechanic burned his fingers again. Examination of the dimmer and attached circuit breakers after their removal revealed scorching around the LV1 lead and scorching on the lower side of both circuit breaker covers.

The dimmer component for an incandescent lamp displayed a manufacturer part number of 2-459 and a serial number of 1175. It was manufactured in July 1970. According to the FAA inspectors, the part appeared to be manufactured by EDC, Lynnwood, Washington. A label, located on the base of the component, indicated it was bench checked on January 20, 1995, by Astro-Aire Enterprises, Oakland, California.

No additional anomalies were noted and a new dimmer component was inserted. No anomalies were reported after the dimmer replacement.

A search of the FAA's Service Difficulty Report Database revealed seven reported incidents involving overheating/burning dimmer control sharing the same part numbers.

The switch and related circuit breakers were sent to the National Transportation Safety Board Materials Laboratory for examination, but were lost in transit.