What happened
On May 3, 2020, at approximately 17:00 LMT, a student pilot was conducting training flights consisting of several circuits at the Piotrków Trybunalski (EPPT) aerodrome. The first two circuits were completed without incident. However, shortly after commencing the third circuit at an altitude of 30 to 50 meters, the engine of the CH601 Zodiak, registration OK-JUA, suffered a sudden failure.
The pilot attempted to restart the engine by switching to the secondary engine control system, but the engine failed to restart. Due to the low altitude and the presence of buildings at the end of the runway, a straight-ahead landing was not possible. The pilot opted for an emergency landing in a nearby field to the right of the flight path, which was intersected by a dirt road.
During the approach, the pilot executed a 90-degree turn with excessive bank and insufficient slip correction, leading to a side-loading landing. The aircraft struck the ground, causing damage to the landing gear and engine cowling. The nose of the aircraft then struck a small embankment near the dirt road, causing the aircraft to pitch upward and begin a vertical rotation, before falling back to the ground and completing a 180-degree spin. There were no fuel leaks or subsequent fire. The pilot sustained no injuries, but the aircraft suffered extensive damage to the landing gear, propeller, engine mounts, engine cowlings, main bulkhead, cabin structure, wingtip, and the rear fuselage.
The investigation
The investigation focused on the cause of the engine failure and the mechanics of the electrical failure. An examination of the engine revealed that a connector within the switch used to select between the primary and backup engine control systems had partially retracted. This retraction interrupted the electrical supply to both the fuel injection and ignition systems.
Technical analysis showed that the switch utilized standard 6.3 mm automotive-style connectors. These connectors are secured by a spring-loaded locking tab and require significant force to mate. The investigation found that the force required for connection could lead to the bending of the locking tab, preventing the connector from being properly seated within the plastic housing.
Findings
- The primary cause of the engine failure was the interruption of electrical power to both the primary and backup fuel injection and ignition control systems.
- This power interruption was caused by the retraction of a connector within the engine control system selection switch.
- The use of automotive-type 6.3 mm connectors, which require high insertion force, contributed to the improper seating of the connector due to potential deformation of the locking mechanism.