What happened
On October 14, 2020, a Guimlar Cabri G2, registration SP-NGU, was conducting a training flight at Dęblin (EPDE) airport. The flight, operated by the Academic Flight Training Center LAW, was intended to practice simulated autorotation maneuvers under VFR daytime conditions.
Prior to initiating the maneuver, the instructor in the left seat opened the left door to allow for greater ease of movement while operating the controls. As the aircraft entered the simulated autorotation at approximately 500 ft AGL, the door initially remained attached via the gas strut. However, due to aircraft vibrations, the door eventually detached from the airframe.
The pilot successfully recovered engine RPM, synchronized it with the main rotor, and continued the approach to the grass runway. The aircraft landed safely without further incident, and the crew sustained no injuries.
Upon post-flight inspection, the crew identified several areas of damage to the airframe, including damage near the left fuel filler, impact marks on the left skid landing gear arc, and damage to the left horizontal stabilizer. The left position light was also destroyed. The detached door was located approximately 922 meters from the threshold of the grass runway and 1130 meters from the touchdown point.
The investigation
The PKBWL examined the mechanical state of the door attachment mechanism and the flight sequence. The investigation focused on why the door failed to remain secured despite the gas strut being engaged. The investigation also reviewed the operator's training procedures and the manufacturer's technical bulletins.
Findings
- The primary cause of the door separation was corroded retaining pins that were intended to prevent the door from sliding out of its hinges.
- The flight manual for the Cabri G2 permits the opening of the door during flight, which contributed to the circumstances of the event.
Safety action
- The operator conducted detailed briefings with instructors, students, and technical personnel regarding crew workload and emergency procedures following a door separation. Pre-flight and post-flight inspection procedures were also reinforced.
- The manufacturer, Guimbal Helicopters, issued Service Bulletin SB 14-005A, which provides for the replacement of hinges with an option that does not require additional pins, as well as instructions for repairing the damaged components.