What happened
On May 4, 2005, at approximately 16:40 local time, a Piper PA-34-200T, registration EC-EUN, was performing a dual instruction flight at Cuatro Vientos Airport in Madrid. During the takeoff roll, after traveling only about 10 meters, the left main landing gear strut failed. This caused the front and left sections of the aircraft to strike the ground.
The aircraft was operated by Aeromadrid, and the crew consisted of an instructor and a student pilot. Both occupants were uninjured and were able to egress the aircraft on their own. At the time of the accident, weather conditions were reported as calm winds with unlimited visibility and clear skies. The aircraft sustained damage to the left flap, the left propeller blades, and the landing gear assembly.
The investigation
Investigators examined the fractured component of the left main landing gear. The analysis focused on the piston located inside the cylinder of the gear strut, specifically at the junction with the fork holding the wheel axle.
Maintenance records indicated that the aircraft had undergone its required 100-hour and 1,000-hour inspections in accordance with the approved maintenance program. While a previous Airworthiness Directive (FAA 94-13-11) had required the replacement of the main structural trunnion after 2,000 hours of service, this specific component had been replaced in 2000. However, that directive did not mandate the replacement of the piston, which was subject to inspection rather than automatic replacement.
Findings
- The investigation determined that the failure of the piston was caused by material fatigue.
- Microscopic analysis of the fracture surface revealed typical fatigue striations (beach marks) indicating progressive cracking.
- The fracture originated near the through-hole of the bolt securing the piston to the fork, a high-stress concentration area.
- The final failure occurred when the crack reached a critical length, leading to a static rupture of the remaining material.