What happened
On April 27, 2020, a Guimbal Cabri G2 helicopter, registration SP-NAL, was conducting a VFR daytime training flight on a route between Dętend, Lublin Radawiec, and Dęblin. The flight was operated by the LAW Academic Flight Training Center.
During the flight, the student pilot adjusted the collective pitch and power lever friction brake to the required 80% power setting. However, upon arrival at Lublin Radawiec, the crew discovered that the friction brake lock could not be released. After attempting to unlock the mechanism at a safe altitude without success, the crew decided to return to the departure airfield in Dęblin.
Upon approaching Dęblin, the crew received authorization to perform a fixed-wing style landing on the grass runway. Under the instructor's direction, the student pilot applied significant force to the collective pitch and power lever, successfully reducing the power to 40% and allowing for a safe landing.
The investigation
The PKBWL investigation focused on the mechanical failure of the control lever mechanism. Following the incident, the aircraft was grounded for technical inspection. Maintenance personnel examined the friction brake of the collective pitch and power lever, subsequently cleaning and lubricating the brake knob.
Findings
- The primary cause of the incident was the jamming of the friction brake lock knob on the collective pitch and power lever.
- There were no contributing circumstances identified for the occurrence.
Safety action
- The operator conducted a detailed review of the incident with flight instructors, civilian and military students, and technical personnel, specifically emphasizing the proper use of the collective pitch and power lever friction brake during operations.