What happened
On August 31, 2013, a Cessna C152, registration OK-OGC, was conducting a training flight near the LKRICA airfield when the engine began running irregularly. The flight, which was part of a navigation training syllabus, was being conducted by an instructor and a student pilot. During the descent, the crew attempted various fuel valve and mixture adjustments, believing the engine instability might be caused by air bubbles or debris in the fuel lines.
While the engine briefly recovered, the instability returned during a climb attempt back toward Letňany airfield. Realizing the aircraft could not reach its destination, the instructor took control and performed an emergency landing in a field covered with tall vegetation north of the LKRICA airfield. The aircraft landed without structural damage, and the crew escaped without injury.
The investigation
The ÚZPL and investigation focused on the fuel management procedures and the accuracy of the fuel readings prior to takeoff. The investigation established that the aircraft was equipped with long-range tanks, but the fuel gauge for the right tank was non-functional. This defect had not been recorded in the maintenance logs, nor was the gauge clearly marked as inoperative.
To compensate for the faulty gauge, the operator provided a homemade wooden dipstick. However, testing revealed that this amateur-made measuring tool was significantly inaccurate. Due to the non-linear nature of the tank profile, the wooden stick overestimated the remaining fuel by as much as 20 to 30 liters compared to an original manufacturer's gauge. While the crew believed they had approximately 90–100 liters of fuel remaining, the actual usable fuel had been depleted.
Findings
- The engine failure was caused by the complete exhaustion of usable fuel.
- The crew relied on an incorrectly calibrated, homemade dipstick to estimate fuel levels, which prevented an accurate determination of the remaining fuel.
- The pilot did not immediately recognize the engine irregularities as fuel exhaustion, instead focusing on troubleshooting the fuel system, which led to the loss of a suitable landing site.
- The aircraft was operated with a known but undocumented fuel gauge failure, and the replacement measurement method provided by the operator was unreliable.