What happened
On August 28, 2020, at approximately 12:00 LMT, a Skyline Towmaster and a Let L13 Blanik glider departed from runway 23L at Leszno (EPLS) for a training flight in preparation for upcoming airshows. The planned release altitude for the glider was 1,300 meters.
While flying at an altitude of approximately 900 meters, the engine of the Skyline Towmaster experienced a failure. Upon noticing the loss of power, the glider pilot performed a self-release. The aircraft pilot attempted to restart the engine five times without success and declared an emergency to the air traffic controller, deciding to land the aircraft. Due to the sufficient altitude and proximity to the airfield, a safe approach was maintained. During the final approach to runway 2 and at an altitude of approximately 300 meters, a final restart attempt was successful, allowing the pilot to land on runway 23L with a functioning engine.
The investigation
Following the incident, a visual inspection of the fuel gauge indicated that the fuel level was below the red zone (less than 1/4 tank), suggesting no more than 12 liters remained. To determine the exact quantity, 43 liters of fuel were added to the single tank located in the right wing. Given the total tank capacity of 47 liters, investigators established that only 4 liters of fuel had been remaining in the tank.
Investigation of the fuel system revealed that the fuel gauge readings are subject to an error of approximately 5 to 8 liters depending on the terrain slope where the aircraft is parked. The pilot had estimated that the fuel level shown on the gauge was sufficient for one hour of flight, but failed to account for the potential error caused by the aircraft's parking position on uneven ground. Furthermore, the fuel tank lacks baffles to prevent rapid fuel movement during maneuvers.
Findings
- The primary cause of the engine failure was fuel starvation resulting from an incorrect pre-flight calculation of the fuel required for the mission.
- The pilot relied on a fuel gauge reading that did not account for inaccuracies caused by the aircraft's orientation on uneven ground.
- The fuel tank is not equipped with baffles to mitigate fuel sloshing during flight maneuvers.
- The fuel gauge error margin (5-8 liters) significantly impacted the pilot's ability to accurately assess remaining endurance.