What happened
On December 11, 2021, an instructor and a student pilot were performing circuit training at Gliwice Airport (EPGL) in a Schweizer 269C, registration SP-KGO, as part of a Commercial Pilot License (CPL(H)) training program. During the third turn of a circuit, the crew noticed vibrations throughout the aircraft and observed the helicopter drifting to the left of the intended flight path. Simultaneously, unusual noises were heard coming from the engine.
Within one minute, a loud bang originated from the engine compartment, followed by a significant loss of engine power and a decrease in main rotor RPM. The crew immediately initiated an autorotation procedure. The helicopter performed an emergency landing at the airport, which resulted in no injuries and no damage to the airfield.
The investigation
The PKBWL examined the engine's mechanical condition and the integrity of the oil system. The investigation focused on the source of the vibrations and the sudden loss of engine power. The crew's qualifications, medical certifications, and the aircraft's documentation and insurance were all found to be in order. Meteorological conditions at the time of the event were determined to have no impact on the occurrence.
Findings
- The primary cause of the event was a drop in oil pressure caused by a leak in the oil line, which led to the seizure of the engine during flight.
- A fatigue crack developed in one of the brackets securing the oil installation line.
- This crack allowed the oil line to come into contact with a sharp edge on one of the oil cooler components.
- Ongoing aircraft vibrations and the contact with the sharp edge caused progressive wear and damage to the oil line, eventually leading to the leak and the rapid loss of oil pressure.