What happened
On July 2, 2010, a Z-37A aircraft, registration OK-CJV, was performing agricultural spraying operations near the village of Kočín. After completing several sorties, the pilot attempted to fly to a new target area near Žebnice. During the flight, at an altitude of approximately 60 meters, the pilot noticed the aircraft was failing to climb and heard an unusual engine sound, described as a "buffeting."
At this moment, the pilot also received a stall warning. Believing a spark plug had failed, the pilot attempted to execute a right-hand turn to use the downward slope of the terrain to regain airspeed. However, the aircraft continued to descend. At a very low altitude, the pilot decided to perform an emergency landing in a nearby field of rape. During the descent, the aircraft entered a slight right turn, lost speed, and struck the ground. The impact caused the engine to tear from its mounts, the landing gear to collapse, and a subsequent fire to destroy the airframe. The pilot sustained serious injuries but managed to exit the cockpit before the fire spread.
The investigation
The ÚZPLN investigation focused on the engine's performance and the aircraft's weight configuration. Investigators examined the engine and propeller, as well as the spark plugs. The investigation also reviewed the environmental conditions, specifically the high ambient temperature, which was approximately 29.5°C at the time of the accident.
Technical analysis of the engine revealed that one spark plug was completely non-functional and two others were functioning irregularly. Furthermore, the porcelain insulation on the high-voltage lead for cylinder number five was found to be broken. The investigation also confirmed the aircraft's weight was near its maximum takeoff weight (MTOM) for the given conditions, as the aircraft was carrying 500 kg of chemical granules and approximately 72 kg of fuel.
Findings
- The primary cause of the accident was a reduction in engine power caused by an unexpected ignition system failure.
- The combination of high ambient temperatures and the aircraft operating at the upper limit of its permissible takeoff weight significantly reduced the aircraft's performance margins.
- The pilot underestimated the impact of the environmental conditions on the aircraft's climb capability.
- The decision to execute a turning maneuver at low speed and low altitude led to an unavoidable loss of airspeed and the subsequent impact.
- The pilot did not have sufficient time to perform emergency procedures, such as jettisoning the chemical load, due to the critical nature of the situation.