What happened
On April 18, 2005, at approximately 11:00 local time, a Grumman G-164 A Super Ag-Cat, registration EC-CZC, was performing a solo familiarization flight at the Palma del Río Aerodrome in Córdoba, Spain. Prior to departure, the pilot had completed refueling, drained the tanks to check for contaminants, and performed all necessary engine warm-up and taxi procedures without detecting any abnormalities.
During the initial climb phase after departing from runway 25, the pilot noticed the engine began to fail. The pilot executed an emergency maneuver, turning right to reach a field located approximately 70 and 700 meters from the runway. The aircraft landed on the terrain but traveled 17 meters before the aircraft overturned. While the aircraft sustained significant damage, the pilot was able to exit the cockpit uninjured.
Witnesses on the ground, including two mechanics, reported that the takeoff appeared normal, but observed a series of explosions accompanied by black and white smoke following the aircraft's turn, which continued until the impact with the ground.
The investigation
The investigation focused on the mechanical state of the Pratt & Whitney R-1340-AN1 engine and the structural integrity of the aircraft following the impact. Investigators examined the wreckage and found that the main landing gear and the wing spar had broken. The propeller blades were bent backward, indicating the aircraft struck the ground at a low speed and with low power.
Technical inspection of the engine revealed that the rocker arm shaft for the exhaust valve of cylinder number 2 was missing. This failure prevented the rocker arm from functioning as a lever to compress the valve spring, leaving the exhaust valve permanently closed. Consequently, high-temperature combustion gases remained trapped within the cylinder. The presence of soot, carbon, and greenish deposits on the spark plugs—indicative of melting copper from the electrodes—confirmed that the engine was operating under extreme thermal stress.
Findings
- The primary cause of the accident was an engine failure caused by the breakage and loss of the rocker arm shaft for the exhaust valve of cylinder number 2.
- The loss of the shaft prevented the exhaust valve from opening, leading to trapped high-temperature gases that flowed back into the intake manifold.
- This malfunction caused irregular combustion, engine explosions, heavy smoke emissions, and a significant loss of power.
- The investigation could not determine the specific reason for the shaft's breakage because no fragments of the component were recovered from the wreckage.