What happened
On August 2, 2003, a Piper Seneca PA-34, registration EC-FMX, was conducting a dual instruction flight from Cuatro Vientos Airport to Son Bonet Aerodrome in Palma de Mallorca. The flight, which included an instructor and three students, lasted approximately 2 hours and 25 minutes.
Upon arrival at Son Bonet, the aircraft entered the traffic pattern for an approach to runway 24. During the landing phase, the aircraft experienced a hard touchdown. While taxiing toward hangar 2, the nose gear strut failed, causing the aircraft to tilt forward and resulting in the propellers striking the ground. All four occupants evacuated the aircraft safely, and there were no injuries, though the aircraft sustained minor damage.
The investigation
The investigation focused on the structural integrity of the nose gear assembly. The nose gear strut is attached to the airframe via a fixed cradle consisting of an inverted V-shaped main element and four supporting tubes. Because this component is not easily accessible, it can only be inspected thoroughly by removing the nose section of the aircraft.
Investigators examined the cradle after it was removed from the aircraft. The inspection revealed fractures in tubes A and B at the junction with the main node, as well as damage to tube C. Metallurgical testing was performed to determine if the failure originated from a material defect or external force. The analysis confirmed that there were no inherent metallurgical defects in the cradle components themselves, and the tubes outside of the weld zones showed hydrogen levels low enough to not affect mechanical behavior.
Findings
- The investigation identified that the welding process used to attach tube A to the cradle node introduced an excessive amount of hydrogen into the metal.
- This high hydrogen content caused hydrogen embrittlement in the affected weld zones.
- The fracture in tube A exhibited characteristics of a brittle fracture caused by this embrittlement.
- The remaining fractures in the other tubes were consistent with static overload following the initial failure.