What happened
On May 14, 2011, a Zlín Z 50M, registration OK-XRK, was performing a training flight near Benešov when the engine failed. The pilot, who was conducting maneuvers in the area, noticed irregular engine behavior and a drop in oil pressure while attempting to increase power during his approach to the airfield.
As the aircraft continued its descent, the oil pressure dropped to zero, resulting in a complete engine failure. The pilot initially considered landing in an area near the Semovický pond but rejected the option due to the need for a significant course change and the presence of overhead power lines. Instead, the pilot opted for an emergency landing in a field behind the pond, heading toward runway 24.
The landing site was covered in dense, tall beet crops approximately one meter in height. Although the pilot executed the landing procedure correctly, the thick vegetation caused an abrupt deceleration. The resulting inertial forces caused the aircraft to nose over and capsize onto its back. The pilot was able to exit through the broken canopy and escaped without injury.
The investigation
The ÚZPLN investigation focused on the mechanical failure of the engine and the circumstances of the landing. Investigators examined the engine's oil system and identified a failure in a rubber seal (part no. Sc3770) located at the junction of the lubrication channel on the fuel injection pump flange. This failure caused oil to leak progressively, leading to the drop in oil pressure.
Technical analysis confirmed that once the oil pressure fell below 100 kPa, the engine's fuel pump automatically switched to a rich mixture setting, which subsequently caused the engine to shut down. The investigation also noted that the dark smoke observed by a nearby helicopter pilot was likely an aerosol of escaping oil and unburned fuel rather than fire. The investigation found that the pilot's decision-making regarding the landing site was appropriate given the hazards of power lines and the need to maintain directional control.
Findings
- A sudden failure of a rubber seal in the engine's oil installation led to a loss of oil pressure.
- The engine shutdown was a result of the automatic fuel pump adjustment triggered by low oil pressure.
- The aircraft overturned due to the high resistance and abrupt deceleration caused by the dense beet crop during the emergency landing.
- The pilot was properly qualified and the aircraft was fully compliant with all maintenance and airworthiness requirements.