Incident Description
According to the captain, the flight and landing were uneventful, and the airplane was parked at the gate. The parking brake was set, the nosewheel steering was shut off, and the seatbelt sign was turned off. The ground power unit was connected, the green "AVAIL" light on the overhead panel illuminated, and the captain selected ground power. He stated he then turned off the No. 2 generator, and, at that "exact moment ... we observed a momentary flash of cabin and cockpit lights, and ... simultaneously ... the nose gear collapsed."
Examination Findings
Examination of the airplane's nose landing gear selector valve revealed slack in the lock wire on the spanner end cap, and the spanner end cap was backed off. Test bench examination of the unit revealed an internal hydraulic fluid leak, and disassembly examination revealed glyd rings No. 1 and No. 4 were damaged. The lock wire, end cap, and glyd ring conditions were the subject of two previous service bulletins, one from the valve manufacturer, Tactair, and one from the airplane manufacturer, Bombardier.
Service Bulletins
Tactair had issued its service bulletin dated March 12, 2003, effective for valve serial numbers 0001 to 0645; the incident airplane's nose landing gear selector valve was serial number 550. Bombardier had issued a service bulletin dated May 29, 2003, with Revision "A" dated June 12, 2003, that directly referenced the Tactair service bulletin and was distributed to each airplane operator. The Bombardier service bulletin, however, incorrectly listed its effectivity; it stated the service bulletin applied to Bombardier airplane serial numbers 7045 thru 7067 and 7069 thru 7189. The incident airplane was Bombardier serial number 7192, and selector valve serial number 550 was original equipment for that airplane. The service bulletin is being revised.