What happened
On December 29, 2015, a Cessna 172RG, operated by Omni Aviation Training Center, was conducting an instrument flight training mission from Cascais (LPCS) to Faro (LPFR). During the flight, the crew performed a low pass after a discontinued approach at Faro. During the subsequent landing gear retraction, the crew heard an unusual mechanical noise, though the position indicator initially suggested the gear had retracted correctly.
Upon attempting a new approach using the ILS for runway 10, the crew observed that the landing gear position indicator was not showing the gear as down and locked. The instructor pilot physically confirmed that the right main landing gear wheel was not in its normal position. After attempting several maneuvers to lock the gear in the extended position without success, the crew decided to perform an emergency landing on runway 17 at Cascais.
The aircraft touched down intentionally slightly to the left of the runway centerline, first with the left main gear and then the nose gear. When the unlocked right main landing gear made contact with the ground, the aircraft began a rightward rotation, eventually coming to rest at an 80-degree angle to the runway heading. The aircraft sustained substantial damage to the landing gear, the lower rear fuselage, the right wing tip, the stabilizer, and the elevator. The crew and passenger escaped without injury.
The investigation
The GPIAAF investigation focused on the mechanical failure of the landing gear system. Technical analysis of the right main landing gear actuator (P/N: 9882015-2; S/N:6891) revealed that the component was fractured and slightly deformed.
Specialists from the Instituto Superior Técnico performed a materials analysis, which determined that the fracture developed along a longitudinal plane relative to the axis of the holes and the ring. The investigation noted that the existing inspection methods, based on Textron Aviation's SEB01-2, were dependent on the component exhibiting visible cracks, which was not always sufficient for detection. The investigation also found that the airworthiness management organization (Part M) had not effectively controlled inspections or assessed the specific risks of operating an aging aircraft in a high-cycle training environment.
Findings
- The right main landing gear actuator suffered a fracture that prevented the gear leg from operating normally.
- The failure mode of the component was rapid, making the existing inspection methods the only defense against catastrophic failure.
- The maintenance program for the aircraft did not adequately account for the increased risks associated with the high-cycle nature of flight training operations.
- The current component design and inspection requirements were insufficient for the reliable detection of such fractures before failure.