What happened
On March 13, 2007, a Bombardier DHC-8-402, registered JA849A, operating as All Nippon Airways flight 1603, experienced a landing gear malfunction during a scheduled flight from Osaka International Airport to Kochi Airport. While the aircraft was on approach to Kochi, the crew discovered that the nose landing gear would not extend.
Following the discovery, the crew performed several troubleshooting maneuvers. They conducted two low passes over the runway to check the status of the nose gear doors and attempted to use aerodynamic forces—including a steep turn and a touch-and-go maneuver—to force the gear into position. The crew also utilized the manual alternate extension system, but the gear remained retracted.
As fuel levels became a concern, the pilot in command decided to proceed with a landing. To mitigate the impact, the crew moved several passengers to the rear of the aircraft to adjust the center of gravity and prepared for a potential emergency evacuation. The aircraft touched down on its main gear at 106 knots; approximately 12 seconds later, the nose descended and struck the runway surface. The impact caused damage to the forward lower fuselage. There were no injuries among the 6 and 56 passengers and crew on board.
The investigation
The investigation examined the aircraft's maintenance history, the flight data recorder, and the cockpit voice recorder. Investigators also analyzed the nose landing gear door linkage mechanism. The inquiry included technical reviews of the manufacturing and repair processes at Bombardier Inc. and Goodrich Corp. to determine why the gear failed to deploy.
Findings
Technical analysis revealed that the nose landing gear doors remained closed because a spacer had migrated out of the toggle link assembly. This movement caused the spacer to interfere with a support fitting, effectively jamming the entire door linkage mechanism.
This migration was caused by the absence of a bolt and nut during a previous repair in the manufacturing process. Without these securing components, the spacer was gradually pulled out of position by the combined effects of gear retraction/extension cycles, airframe vibrations, and aircraft acceleration during flight operations.