What happened
On October 3, 2003, a Piper PA-23-250, registration EC-GLA, departed from Cuatro Vientos Airport (Madrid) for a test flight following a scheduled 100-hour maintenance inspection. The flight was being conducted by two experienced flight instructors to verify engine and system performance.
During the third takeoff and landing cycle, the crew noticed the nose gear unsafe warning horn activate upon touchdown. Although the nose gear appeared visually extended through the engine nacelle mirror, the cockpit indicator light remained unlit. The crew performed several attempts to secure the gear, including cycling the landing gear and using the manual hydraulic pump, but the nose gear indicator failed to show a locked position.
The crew decided to return to the airport, notifying air traffic control and requesting fire services to be on standby. To minimize fire risks, the crew proactively shut down non-essential electrical systems before landing. During the landing roll, the nose gear collapsed forward, causing the aircraft's fuselage to drag along the runway. The aircraft came to a stop approximately 14 meters after the collapse, resulting in damage to the lower fuselage, antennas, and both propellers.
The investigation
Investigators examined the nose gear assembly and discovered that the right-side fitting for the upper drag link attachment had broken. A specific bolt (P/N AN6-43) used to secure the drag link had failed.
Technical analysis revealed that the bolt had previously suffered a fatigue fracture near the left fitting. This failure caused the remaining portion of the bolt to bend under the load, eventually leading to the tearing of the right-side fitting. The investigation also noted that while the aircraft had recently undergone a 100-hour inspection, the critical component in question was subject to a different inspection interval. Specifically, the 1,000-hour airframe inspection, performed earlier in July 2003, was the interval during which this specific bolt should have been removed and inspected for defects.
Findings
- The primary cause of the incident was the fatigue failure of the nose gear upper drag link bolt.
- This failure prevented the nose gear from properly locking in the down position and eventually led to the structural collapse of the nose gear assembly during the landing roll.
- The failure of the bolt caused the drag link to lose its proper alignment, triggering the cockpit warning horn.
- The crew's decision to perform a go-around and their subsequent emergency procedures during the landing were considered highly effective and appropriate.