What happened
On May 9, 2014, at approximately 08:35 UTC, a Z-37A aircraft, registration OK-ZJG, was performing agricultural spraying operations near Chvalkovice, Czech Republic. The pilot was conducting a low-level maneuver to treat a field with fertilizer granules at an altitude of approximately 25 to 30 meters.
During a turn toward a slight slope, the aircraft encountered an unexpected and extremely strong wind gust. This sudden atmospheric disturbance caused the aircraft to experience a rapid increase in the angle of attack and a significant roll. The pilot attempted to recover by applying full left control and advancing the throttle and propeller levers. In an effort to lighten the aircraft, the pilot also jettisoned the fertilizer spreader. However, the aircraft lost airspeed and entered a critical state, causing the right wingtip to strike the ground. This initial impact led to a sequence of further strikes, including the propeller and fuselage hitting the earth, which ultimately caused the engine to be torn from the airframe and the aircraft to capsize. The pilot sustained serious injuries and was trapped in the deformed cockpit until rescued by emergency services.
The investigation
The ÚZPLN investigation examined the aircraft's maintenance records, the pilot's experience, and the meteorological conditions at the time of the accident. Technical inspections of the Z-37A revealed no evidence of mechanical failure prior to the impact; the engine and propeller were found to be in good working order and were likely operating at flight power during the crash. The investigation also analyzed the wreckage, noting that the spreader was jettisoned just before the wing struck the ground, and reviewed witness testimony from a bystander who observed the aircraft struggling to maintain control after being hit by a gust of wind.
Findings
- The pilot was highly experienced in agricultural flight operations with the Z-37A.
- The aircraft was fully airworthy and had no pre-existing mechanical defects.
- Meteorological conditions involved significant thermal turbulence and gusty winds, with gusts measured at up to 12 m/s at 20 meters AGL.
- The pilot was performing a maneuver in a challenging environment, flying against a slight slope with a tailwind or side-wind component.
- The primary cause was an aerodynamic stall resulting from an excessive angle of attack caused by sudden, intense thermal turbulence.