What happened
During an international passenger flight operating under Title 14, CFR Part 121, the flight crew observed smoke and smelled burning in the cockpit. The incident occurred shortly after a crew change that necessitated opening and closing the cockpit security door. The pilot declared an emergency and diverted to the nearest airport, where the aircraft landed without further incident. There were no injuries reported.
The investigation
An examination of the reinforced cockpit door, which had been modified under STC ST01391LA, was conducted by maintenance personnel and the NTSB investigator-in-charge. Investigators discovered that excess wiring used to power the electrically operated locking solenoid was resting on top of the unshielded, metal-encased solenoid inside the doorframe. While some wires were protected by a plastic anti-chafe mesh, a portion of this mesh had melted and emitted a burnt plastic odor.
Maintenance records showed the door conversion was completed on March 21, 2003, and the unit had accumulated approximately 16,416 flight hours and 1,170 cycles. While the installation instructions included a caution regarding the need for the security bolt to engage fully to prevent the solenoid from overheating, the instructions did not specifically address how to secure excess wiring located above the striker/solenoid unit. Although an aircraft warning light exists to indicate if the solenoid remains energized, the crew did not report seeing this light during the flight, and ground tests of the mechanism were successful.