What happened
On July 28, 2010, a GRUMMAN AA-5A, registration EC-DAB, was performing a private VFR flight returning to Valencia Airport. While descending through approximately 1,200 feet between the Sagunto and El Puig points, the pilot reduced the throttle to initiate the descent. Upon attempting to increase engine power to reach the desired altitude, the pilot observed that the engine failed to respond to throttle movements, remaining fixed at 1,800 rpm.
Despite the pilot attempting to use the auxiliary fuel pump and adjusting the fuel selector, the engine power remained insufficient to maintain altitude. Realizing the aircraft could not reach the airport, the pilot declared an emergency and identified a suitable landing site in an orange grove. During the emergency approach, the aircraft struck the treetops of several rows of trees, causing the aircraft to rotate 180 degrees and strike further trees. The impact caused significant damage to the wings and the loss of the nose gear, though the fuel tanks ruptured without causing a fire. The pilot and one passenger were uninjured.
The investigation
Investigators examined the engine and cockpit controls, finding the throttle lever in the aft position and the mixture cut off. A detailed inspection of the engine revealed that the throttle control cable had become disconnected from the carburetor linkage because the securing nut for the bolt had been lost.
Technical tests demonstrated that the friction between the cable terminal and the bolt head was insufficient to prevent the bolt from rotating when the nut was turned. Investigators also reviewed maintenance records, noting that a 50-hour inspection had been performed on the aircraft 27 hours prior to the accident, which included the disassembly and reassembly of the carburetor.
Findings
- The engine did not suffer a mechanical power failure; rather, the pilot was unable to increase power because the throttle cable was disconnected from the carburetor linkage.
- The loss of control was caused by the loss of the securing nut on the throttle cable bolt.
- The investigation concluded that the nut was likely installed without the required torque, either because it was only finger-tightened during the recent maintenance or because the applied torque was insufficient to secure the component.