What happened
On January 22, 2009, a CESSNA 172-RG, registration EC-DMR, was conducting an instrument flight rules (IFR) instructional flight from Sabadell Airport. The crew, consisting of a flight instructor and a student pilot, had successfully completed an approach to Reus Airport and was returning to Sabadell.
Upon entering the traffic circuit for runway 31, the crew attempted to extend the landing gear but noticed the associated indicator light remained unlit. A visual inspection confirmed that the right main landing gear leg was not fully extended. The crew followed emergency procedures, contacted the control tower, and performed fly-bys to allow air traffic controllers to verify the asymmetrical gear configuration. After attempting to lower the gear several more times while remaining airborne, the instructor decided to proceed with an emergency landing.
During the landing roll, the instructor managed the aircraft's weight on the left wheel to mitigate impact. However, as the aircraft neared a full stop, the right wing dropped and the wingtip contacted the ground, causing the aircraft to pivot 180 degrees. The aircraft sustained significant damage to the right wingtip, the horizontal stabilizer, the right main landing gear leg, and the nose wheel leg. No injuries were reported to the occupants.
The investigation
The investigation focused on the mechanical failure of the landing gear system. Laboratory analysis of the right main gear actuator revealed three distinct cracks in the annular part near the orifices where the ring joins the tubular body.
Technical examination determined that the fracture mechanism was microvoid coalescence, which is characteristic of a static overload fracture. This type of failure occurs when the material is subjected to tensile loads that exceed its structural capacity. The investigation also considered the aircraft's history, noting it had been used for flight training since 2002, a role that often involves high-stress maneuvers and hard landings.
Findings
- The primary cause of the accident was the fracture of the right main landing gear actuator.
- The fracture was a result of a static overload caused by local stresses in the annular region of the actuator.
- It is probable that the maximum static load capacity of the actuator was exceeded during one or more previous hard landings, which had likely occurred due to the aircraft's intensive use in flight training.
- The resulting cracks weakened the structural integrity of the component, eventually leading to its failure during the flight.