What happened
On the airfield of Theux (EBTX), a Piper PA-18-150 operated by Royal Verviers Aviation was performing glider towing operations. During the pre-flight inspection, the pilot noted that while the left fuel tank was full, the right tank was nearly empty. Following a successful tow and glider release at 3,000 feet, the aircraft returned to the airfield.
During the final approach leg, the pilot realized the aircraft was descending too low and attempted to increase power. However, the engine failed to respond to the throttle input. The aircraft continued to descend into a tree line bordering the airfield. The left wing struck a large tree trunk, causing the aircraft to veer and rotate 1/2 turn before crashing on its nose and undercarriage. The pilot sustained a broken foot and back injuries but managed to exit the wreckage independently.
The investigation
AAIU(Be) investigators examined the wreckage and the engine systems of OO-OAW. Technical inspections of the Lycoming engine, magnetos, and carburetor revealed no mechanical blockages, failures, or obstructions in the air intake. The engine control cables were also found to be intact.
Regarding the fuel system, investigators found that the right tank was empty while the left tank remained full. While the pilot believed the fuel selector was set to "both," evidence suggested the right tank had been selected during flight. The investigation also noted that the aircraft featured a 180HP engine modification (STC SA-00035-NY), which interconnects the tanks to allow a "both" setting. The investigators highlighted that different STC modifications for the same aircraft model can result in significantly different fuel system behaviors.
Findings
- The exact cause of the engine failure could not be definitively identified, but the evidence is consistent with fuel starvation.
- It is possible that after the glider was released, the engine was set to idle, allowing the depletion of the nearly empty right tank to go unnoticed until the pilot applied power for the final approach.
- The investigation noted that the fuel quantity gauges provided unreliable and imprecise readings.
- Potential confusion regarding the fuel tank selector configuration, due to varying STC modifications in similar aircraft types, may have contributed to the error.
Safety action
- The report advises Belgian aeroclub users of Piper PA-150 aircraft equipped with 180HP engines to remain vigilant regarding the significant differences in fuel system configurations between similar aircraft models and to maintain a sufficient safety margin in fuel management.