What happened
On February 29, 2004, a Commander 114B, registration CS-DBH, departed from Tires Aerodrome in Cascais for a local leisure flight. The aircraft was carrying three occupants. Approximately 50 minutes into the flight, while cruising at 2,000 feet on the return leg to the departure aerodrome, the engine ceased operation.
Following several unsuccessful attempts to restart the engine, the pilot declared an emergency to Air Traffic Control and executed an emergency landing in a rural cultivation area. During the landing sequence, the pilot performed necessary emergency procedures, including shutting off the fuel pump and fuel selector, and extending the landing gear. As the aircraft made contact with the ground, the left landing gear touched first, and the aircraft slid approximately 115 meters.
The aircraft struck a low stone wall separating two properties. The impact caused the left wing to strike the wall, inducing a rotation, and the right wing subsequently struck the wall, rupturing the right fuel tank. Despite the significant damage to the airframe and the resulting fuel spill, all three occupants escaped the wreckage without injury.
The investigation
The GPIAAF investigation examined the aircraft's maintenance history, engine performance, and fuel management. The engine was removed and tested on a test bench; it functioned normally during the test, showing no anomalies in oil consumption, cylinder temperatures, or magneto performance. The investigation also reviewed the aircraft's fuel consumption records and refueling patterns.
Investigators analyzed two hypotheses regarding the engine failure. The first considered the possibility of the right tank being empty due to a potential error in fuel selector management. The second hypothesis assumed the fuel selector was in the 'BOTH' position, allowing the tanks to balance via a communicating vessels system. Calculations based on refueling logs indicated that the aircraft likely had sufficient fuel to reach its destination, with the remaining fuel in the left tank estimated at over 20 liters.
Findings
- The engine failure occurred for undetermined causes, as all mechanical components, including the fuel system, ignition, and engine internals, functioned normally during post-accident testing.
- The pilot's refueling practices were inconsistent, ranging from refueling only what was needed to topping off the tanks, which made precise fuel load estimation difficult.
- The aircraft was properly maintained and held a valid Certificate of Airworthiness.
- The pilot successfully executed emergency procedures, which prevented a post-crash fire despite the ruptured right fuel tank.