What happened
On 20 June 2006, a Piper PA-30 Comanche, registration ZS-EVB, departed Wonderboom Aerodrome for a test flight. The flight was being conducted to verify repairs recently performed on the right-hand engine's fuel injector, which had previously suffered from blocked nozzles. The pilot and an aircraft maintenance engineer were on board during the flight.
After approximately forty minutes of normal flight operations, the aircraft experienced a critical loss of power during its final approach. The right-hand engine failed first, followed shortly by the left-end engine. Unable to maintain altitude, the pilot executed a glide toward the runway. During the descent, the aircraft struck a streetlight and a fence before the undercarriage impacted the ground. The aircraft skidded approximately 35 meters from the runway centerline before coming to a complete stop. There were no injuries to the two occupants.
The investigation
SACAA AIID investigators examined the mechanical state of the aircraft and the fuel system following the impact. The investigation focused on why both engines failed despite the pilot having selected the main fuel tanks for the duration of the flight.
Technical analysis of the fuel selector valves revealed a mechanical discrepancy. It was discovered that a previous maintenance adjustment to the selector timing had caused the internal cam to press against two ball bearings simultaneously. This error caused the selectors to leak fuel between the main and auxiliary positions, even when set to the "OFF" position.