What happened
On September 4, 2021, a Cessna 152, registration OK-IKC, was participating in the Zdeněk Běhounek Memorial navigation rally near Kladno. While flying an eastbound leg toward a target point, the pilot performed a maneuvering turn (an 'S-turn') to precisely intercept the course. During this maneuver, the pilot deployed 10° of flaps and slowed the aircraft's ground speed from 65 knots to approximately 36.5 knots.
During this low-speed phase, the aircraft experienced a significant loss of airspeed, leading to a wing drop and a subsequent transition into a dive. Although the pilot attempted to recover from the dive, the aircraft entered a steep climb at an angle of 50 to 60 degrees before losing speed and entering a left-hand spin. The aircraft eventually impacted the ground in a vertical descent, with the right edge of the elevator striking the terrain. The impact caused the total destruction of the aircraft's forward and center fuselage and both wings. The pilot and the navigator, who was seated in the right seat, sustained fatal injuries.
The investigation
The ÚZPLN investigation examined flight data recorder logs, witness testimonies, and the physical wreckage. Investigators analyzed the aircraft's weight and balance, the engine's condition, and the meteorological environment. The investigation also reviewed the competition organizer's procedures regarding secondary surveillance radar (SSR) transponder usage.
Technical examinations of the engine and propeller showed no evidence of mechanical failure or bird strike prior to impact. The propeller deformation indicated the engine was producing power at the moment of impact. Meteorological conditions were found to be favorable for VFR flight throughout the event.
Findings
- The aircraft's maximum takeoff weight was exceeded by approximately 17 kg.
- The aircraft's center of gravity was outside of the permitted limits due to the weight of the navigator and the lack of a proper pre-flight weight and balance calculation.
- The pilot performed an improper maneuver for the intended target interception, leading to a critical loss of airspeed.
- The pilot failed to react appropriately to the onset of the stall and the subsequent dive, likely due to the unexpected handling characteristics caused by the overloaded and unbalanced state of the aircraft.
- The flight was conducted with the secondary surveillance radar transponder turned off.
- The competition organizer did not emphasize the requirement for transponder use, and a practice existed where participants flew with transponders deactivated.