Incident Overview
On 31 August 2013, a Cessna C152, registration OK-OGC, performed a training flight from Prague Letňany airport. The aircraft was operated by Aeroklub Točná. During the return leg, the engine began running irregularly and subsequently failed completely. The instructor took control, executed emergency procedures, and performed a forced landing with the engine inoperative in a field south of the village of Říčany, near the ultralight airfield LKRICA. The aircraft touched down in a field of mature alfalfa. No damage occurred to the aircraft, and neither crew member was injured.
Pre-flight and Flight
The aircraft was borrowed from Aeroklub Točná for the training flight. A handover protocol was completed, noting known issues with the fuel gauge and that fuel quantity should be measured using a supplied dipstick. The protocol did not record the fuel quantity or the date. After the handover, the aircraft was flown to Letňany, where six training flights (total 37 minutes) were conducted without reported defects.
The critical flight was a navigation exercise (lesson 18A-1) with a planned duration of 2 hours 35 minutes. Both the student and instructor checked the fuel level using the homemade wooden dipstick. They estimated the fuel quantity at 90–100 litres based on the level reading “a thumb above the top mark.” According to the pilot’s operating handbook, the required fuel for the planned flight, including a 30-minute reserve, was approximately 65 litres. No refueling was performed, and the flight commenced.
During the return, while south of Říčany, the engine began to run irregularly. The crew decided to land at the nearby LKRICA ultralight strip. While descending and approaching, they experimented with different fuel valve and throttle settings, suspecting air or contamination in the fuel system. Neither pilot checked the fuel quantity indicator. The engine temporarily recovered, and they aborted the landing, beginning a climb toward Letňany. Shortly after, irregular running returned, and the crew realized they could not reach Letňany.
Fuel Measurement Issues
The aircraft was equipped with larger-capacity fuel tanks (38 US gallons total). The cockpit fuel gauges had two separate indicators for left and right tanks. The right indicator was found to be inoperative during the technical inspection after the incident. This defect was not recorded in the aircraft logbooks, and the gauge was not clearly marked as inoperative. Additionally, the installed gauges had a scale of 0–12 US gallons, which did not match the larger tank capacity; this discrepancy was not documented in the flight manual.
Because of the gauge defect, the operator had created a homemade dipstick from a varnished wooden dowel, 12 mm in diameter, with three red marks spaced 14 mm apart. This dipstick was not marked with the aircraft type or registration. After the incident, the operator provided another homemade dipstick with numerical markings and the aircraft registration.
A comparative test was conducted to evaluate the homemade dipstick against an original manufacturer dipstick and a commercially available plastic pipette. It was found that the residual fuel level markings were consistent across all dipsticks. However, at higher fuel quantities, the homemade dipstick significantly overestimated the fuel level. For the level “a thumb above the top mark” as reported by the pilots, the discrepancy was more than 20–30 litres. The actual fuel consumption during the flight was consistent with pre-flight calculations.
Landing
The instructor took control, turned slightly right at low altitude, and touched down in a field of mature alfalfa north of LKRICA. Before touchdown, he switched off electrical equipment, ignition, and closed the fuel valve. The aircraft rolled about 160 meters and stopped. Both crew members exited, confirmed no injuries or damage, and called for assistance. Police arrived and performed breathalyzer tests, both negative. A post-flight technical inspection revealed only residual unusable fuel remained in the tanks. Calculated flight time was 1 hour 51 minutes, with approximately 42 litres of fuel consumed.
After agreement with the LKRICA operator, the aircraft was pushed to the strip, refueled, and after an engine ground test, it was flown back to Letňany without any defects noted.
Probable Cause
The investigation concluded that the engine failure was caused by fuel exhaustion resulting from an incorrect determination of the fuel quantity on board.