Flight History
On 5 August 2008, at 18:40 local time, a Cessna 172 RG (registration EC-HHX) operated by Centro de Formación Aeronáutico Aerofan was conducting a dual instructional flight. The aircraft departed from Madrid-Cuatro Vientos Airport with an instructor and two students on board. The flight included planned stops at Marugán (Segovia) and Robledillo de Mohernando (Guadalajara).
During the return leg, while joining the downwind leg of the traffic pattern at Cuatro Vientos, the crew lowered the landing gear. Aural and visual alarms indicated the gear was not down and locked. Visual inspection confirmed that the right main landing gear leg was only partially extended; the left and nose gear were properly positioned.
The instructor took control and alerted the tower. The aircraft was cleared to remain in the circuit at 4,000 feet. The crew cycled the landing gear several times using both normal and emergency procedures. The left and nose legs operated correctly, but the right leg consistently stopped halfway.
After burning fuel for at least 40 minutes, the aircraft landed on the runway with the gear down. During the landing roll, the right main gear collapsed, causing the aircraft to come to rest on its right wing tip, right horizontal stabilizer, and aft fuselage. The occupants exited without assistance and were uninjured. The aircraft was recovered by airport emergency services and moved to a hangar.
Aircraft and Maintenance Information
The Cessna 172 RG (serial number 172RG-0006) was manufactured in 1980. At the time of the incident, it had accumulated 7,618 total flight hours and 1,855 engine hours. Its airworthiness certificate was valid until 20 December 2008.
Maintenance records show a 200-hour inspection on 16 July 2008 (7,550.05 airframe hours), during which landing gear components were checked. A 50-hour inspection had been performed on 28 June 2008 (7,598.02 airframe hours). The aircraft had incorporated Service Bulletin SIB01-02R2, which requires periodic inspections of the main landing gear actuators using fluorescent penetrant dye. The last such inspection was on 12 June 2008 (7,410 airframe hours), leaving 360 flight hours until the next required check.
Investigation Findings
The actuator from the right main landing gear was removed and bench-tested functionally; the test was satisfactory. Subsequent disassembly revealed a fracture in the rotational axis of the actuator's grooved piece. The fracture was located near the nip where the axis joined the toothed wheel.
Laboratory analysis characterized the material as an Al-Zn aluminum alloy (EN AW-7175) with a hardness of approximately 450 MPa. Metallographic examination showed no defects or corrosion. The fracture surface exhibited features typical of progressive fatigue failure. Longitudinal cracks were found in the grooved area, initiating at groove valleys, sides, and crests.
Friction marks on the actuator's inner walls and cover indicated that the pivot axis had moved both parallel and circumferentially during operation, likely due to misalignment. These motions were considered related to the fatigue failure.
Damage
The aircraft sustained minor damage to the right wing tip and tail cone. The aft fuselage was scratched, and the right horizontal stabilizer was bent upward from bearing part of the aircraft's weight during the landing. The right main gear actuator's rotational axis was broken approximately 3 mm from the actuator housing.