What happened
On July 1, 2015, a CH601 Zodiak ultralight aircraft was conducting a recreational flight following a route from Piotrków Trylaralski (EPPT) via Pajęczno and returning to Piotrków Trybunalski. During the flight, the pilot experienced engine vibrations that progressively increased in intensity. In response to the growing instability, the pilot decided to perform a precautionary landing in a flat field approximately 500 meters in length. The landing was completed successfully without injury to the pilot or the passenger.
Upon inspecting the aircraft following the landing, the pilot discovered that two screws used to secure the propeller cap were missing. It was determined that these screws had unscrewed and fallen out during the flight, which was the source of the vibrations perceived by the pilot as engine instability.
The investigation
The investigation established that the loss of the two propeller cap screws caused the vibrations felt during the flight. The investigation also noted that there was no definitive information regarding whether the pre-flight inspection had been performed with sufficient care. After the missing screws were replaced and a ground engine test confirmed that the vibrations had ceased, the pilot initially intended to depart without the passenger to shorten the takeoff run, but ultimately decided to proceed with the passenger on board. During the subsequent takeoff, a separate accident occurred (registered under number 1219/15), which is being investigated by the aircraft operator.
Findings
- The primary cause of the incident was the unscrewing and subsequent loss of propeller cap mounting screws during flight.
- The loss of these components resulted in the increased engine vibrations experienced by the crew.