What happened
On December 26, 2012, a Cessna 172M, registration EC-GUV, departed from the Casarrubios del Monte aerodrome for a local flight with a pilot and two passengers. During the initial climb, while the aircraft was established in a crosswind component, the engine suffered a total power loss. The pilot attempted an emergency landing on runway 08.
The aircraft contacted the runway approximately 150 meters from the end of the paved surface. The landing involved several bounces, and the pilot was unable to stop the aircraft within the runway limits. The aircraft overran the pavement, struck an embankment, and overturned. All occupants evacuated the aircraft; one passenger sustained serious injuries, while the others suffered minor injuries. The aircraft sustained significant damage.
The investigation
The investigation focused on the engine's mechanical state and the pilot's approach. GPS data from a Garmin onboard unit confirmed a loss of power followed by a descent. The investigation revealed that the aircraft touched down late on the runway at a high speed. The pilot had attempted to lose altitude by pitching the nose down, which inadvertently increased the airspeed and prolonged the float phase.
Mechanical inspection of the Lycoming O-302-E2D engine revealed that the lower spark plug of cylinder number 1 had been dislodged from its housing. Furthermore, the investigation found that the helicoils installed in the cylinder heads of cylinders 2, 3, and 4 were not the specific models required by Lycoming manuals. In cylinder 1, the helicoil was entirely missing, and the threaded area showed extreme wear.
Findings
- The primary cause of the engine failure was the dislodged spark plug, which occurred because of the use of improper, non-specification helicoils.
- The failure to stop the aircraft on the runway was due to the high approach speed and the late touchdown point.
- The use of incorrect thread inserts (helicoils) led to excessive wear on the cylinder head threads, eventually allowing internal cylinder pressure and high temperatures to eject the spark plug.
- The passenger's injuries were aggravated by the fact that the front passenger seat had become detached from its tracks during the impact.
Safety action
- The operator, Fly With Us, S.L., was recommended to update its Maneuvering Manual to clearly differentiate between engine failure procedures for takeoff versus cruise phases.
- The maintenance organization, SINMA AVIACIÓN, S.L., was advised to align its work procedures with aircraft maintenance manuals and specified materials.
- A recommendation was made to AESA to ensure maintenance center procedures comply with EASA Part 145 requirements.