What happened
On April 13, 2006, a Cessna 182 RG, registration EC-DND, was conducting a flight training session consisting of takeoff and landing practice at Sabadell Airport. The flight crew included an instructor, a student pilot, and one additional occupant.
Following the initial takeoff, the crew noticed that the green nose gear down-and-locked indicator light failed to illuminate, accompanied by an audible warning. Despite performing six extension cycles and attempting to use the manual emergency extension system, the gear failed to lock. After consulting with the control tower, which visually confirmed the gear appeared to be in the down position, the crew proceeded with a landing.
During the landing flare, the engine was shut down, and the aircraft touched down on its main gear. The pilot delayed nose wheel contact for as long as possible; however, once the nose wheel made contact with the runway, the nose gear began to collapse. The aircraft briefly transitioned to a three-point roll before the nose struck the pavement, causing the aircraft to skid for several meters before coming to a stop. All three occupants were uninjured.
The investigation
The investigation focused on the failure of the nose gear locking mechanism. Investigators examined the damaged nose gear components and compared the broken locking pins to a new, standard-specification pin.
Laboratory analysis revealed that the broken pins had undergone a process of progressive fatigue cracking. These cracks originated at the base of the pin's groove due to asymmetric bilateral loads during the gear's extension and retraction cycles. Furthermore, the investigation found that the broken pins did not match the dimensions of the manufacturer's specifications. The broken pins were approximately 5.8 mm shorter in their seating length and had a groove width of roughly 2.5 mm, compared to the 1.3 mm width found on the standard sample. Additionally, the ends of the broken pins showed evidence of being modified with a grinding tool.
Findings
- The nose gear collapse was caused by the failure of the locking pins that secure the nose gear in the down position.
- The pins failed due to progressive fatigue cracking caused by alternating stresses during gear operation.
- The pins installed in the aircraft were non-standard, having been modified or incorrectly sized, which significantly reduced their structural resistance.
- The reduced seating length and increased groove width made the pins susceptible to the asymmetric loads encountered during flight operations.