What happened
On December 24, 2015, a Socata TB-9, registration EC-LIQ, departed from the Tomás Fernández Espada aerodrome in Villamartin for a private local flight. The aircraft was carrying a pilot and one passenger. The flight path was intended to take the aircraft toward Ronda via Zahara de la Sierra.
Approximately fifteen minutes into the flight, the aircraft was flying at an extremely low altitude over a field near Monte Sauco. The aircraft was observed by witnesses flying very low and slow. While attempting to climb out of a valley, the aircraft struck a large oak tree. The impact caused the right wing and the propeller assembly to detach, and a fire subsequently broke out, destroying the aircraft. Both the pilot and the passenger sustained fatal injuries.
The investigation
The investigation examined the aircraft's maintenance history, fuel logs, and engine condition. Investigators found that the aircraft's certificate of airworthiness had expired ten months prior to the accident. Furthermore, the aircraft and engine logbooks had not been updated since early 2015, and the maintenance status was found to be deficient.
An inspection of the Lycoming engine revealed evidence of improper maintenance, including improperly torqued spark plugs and loose carburetor screws. Crucially, the engine showed signs of long-term use of unleaded gasoline that did not meet the manufacturer's specifications. Witnesses also confirmed the pilot frequently refueled the aircraft using 95-octane automotive gasoline from portable containers because aviation fuel was unavailable at his home base.
Findings
- The engine stopped due to the use of unauthorized automotive fuel, which does not meet the requirements of Lycoming Service Instruction No. 1070S.
- The aircraft was operating with a very low fuel quantity, which, combined with an aggressive climbing maneuver, likely prevented sufficient fuel from reaching the engine.
- The pilot was flying at an altitude significantly lower than the minimums required by Spanish Air Traffic Regulations.
- The aircraft was being operated with deficient maintenance and an expired certificate of airworthiness.
- The presence of a passenger increased the aircraft's weight, which hampered climb performance and increased fuel consumption during the low-altitude flight.