What happened
On 13 September 2020, a Piper PA-28-161, registration G-BZDA, was conducting a training flight at White Waltham Airfield. While climbing through 100 feet following takeoff, the engine power abruptly decreased. The instructor took control of the aircraft, lowered the nose to search for a landing site, and issued a MAYDAY call.
During this maneuver, the engine power recovered, prompting the instructor to attempt to climb away. However, the engine power failed a second time and the engine stopped completely. To avoid an oncoming railway line, the instructor performed a hard left turn toward open ground and executed a forced landing. During the impact, the nosewheel collapsed, causing damage to the propeller blade and the left wing root skin. Both the student and the instructor escaped the aircraft without injury.
The investigation
The AAIB investigation focused on the cause of the engine power loss and the state of the aircraft's fuel system. Although the aircraft was originally manufactured with a non-locking gascolator drain, investigators discovered that G-BZDA had been fitted with a lockable version of the valve.
Upon inspection of the scene, the airfield fire service noted fuel leaking from the gascolator drain. The investigation examined the history of gascolator drain designs, noting that the manufacturer had moved away from lockable valves in the late 1980s because they posed a safety risk. The investigators could not determine when or how the incorrect, lockable valve was installed on this specific aircraft.
Findings
- The engine power loss was caused by partial fuel starvation.
- The fuel starvation resulted from the gascolator drain valve being inadvertently left in the locked open position following a fuel sample.
- The presence of a lockable drain valve on an aircraft that should have been equipped with a non-locking variant created a significant hazard.
- The instructor had performed a fuel sample check during the transit check prior to takeoff, which involved using the gascolator drain.