What happened
On January 17, 2013, a private PA-60-601P (Aerostar 601P), registration EC-ICG, was performing a landing on runway 28 at Cuatro Vientos Airport in Madrid, Spain. The flight had originated from Axarquia Aerodrome. While the approach was normal, the aircraft's nose landing gear collapsed immediately after the main gear made contact with the runway. The nose of the aircraft slid along the asphalt, causing friction-related damage to the fuselage and wheel well doors, before coming to a stop in the final third of the runway. The two occupants, the pilot and one passenger, were uninjured and evacuated the aircraft safely.
The investigation
The CIAIAC investigation focused on the structural integrity of the nose landing gear and the maintenance history of the aircraft. Investigators examined the U-beam that houses the axis for the nose gear's upper drag link. Post-incident inspections revealed that this beam was broken and had lost the rivets that attached it to the side bulkhead. Laboratory analysis of the aluminum alloy component identified a fatigue process characterized by cracks in the rivet holes and at a previously repaired area. The study concluded that the fracture sequence began with the development of fatigue cracks, which eventually led to a ductile tearing mechanism under excessive stress.
Additionally, the investigation noted that the pilot had observed the nose gear doors being partially open during pre-flight checks on recent flights, a symptom of the structural degradation. While a previous crack had been detected and repaired in 2011, the repair did not prevent the subsequent failure, and there were no specific maintenance requirements in the aircraft's program to monitor this particular internal beam for cracks.
Findings
- The primary cause of the incident was a generalized fatigue process that led to the fracture of the support structure for the upper drag link on the nose gear.
- The structural degradation caused the nose gear to lose its rigidity, allowing the leg to move excessively and strike the wheel well's aft bulkhead during the landing run.
- The failure of the beam caused the breakage of the hydraulic return line for the gear actuator.
- There were no specific airworthiness maintenance instructions or requirements to inspect the internal U-beams for fatigue cracks.
- The aircraft's maintenance program did not include monitoring for cracks in this specific structural component, which allowed the fatigue to progress undetected.