Incident Description
On 27 April 2020, a training flight was planned from Dęblin Airport (EPDE) to Lublin Radawiec and back, operated by the Academic Centre for Aviation Training of the Polish Air Force University. The aircraft was a Guimbal-Cabri-G2 helicopter, registration SP-NAL. The flight was conducted under VFR-day rules. After takeoff, the student pilot set the friction lock on the collective and throttle lever to the required 80% power setting.
Upon arrival at Lublin Radawiec, while approaching to land, the student pilot found that the friction lock could not be released. Maintaining a safe altitude, the crew attempted to unscrew the friction lock but failed. Consequently, they decided to return to the departure airport.
After arriving back at Dęblin, the crew received clearance to perform a "samolotowym" (airplane-style) landing on the grass runway. During the approach, on the instructor's command, the student pilot forcefully moved the collective and throttle lever, reducing power to 40%. This power setting allowed the crew to safely complete the airplane-style landing.
Cause
The incident was caused by jamming of the friction lock knob of the collective and throttle lever.
Aftermath
The helicopter was grounded pending inspection. Technical personnel examined the friction lock, then cleaned and lubricated the knob. The helicopter was subsequently returned to service. The investigating entity conducted a detailed briefing with instructors, civilian and military students, and technical staff, emphasizing the proper handling of the friction lock during operations. No additional safety recommendations were issued.