Incident Overview
On 14 October 2020, at 13:17 local time, a training flight was planned at the Academic Centre of Aviation Training in Dęblin, Poland, involving a Guimbal-Cabri-G2 helicopter (registration SP-NGU). The exercise was to simulate an autorotation. The instructor in the left seat had opened the left door for easier access to the throttle and collective controls. After entering the autorotation, the initially ajar door remained held by the gas spring. Due to vibrations at an altitude of 500 feet AGL, the door separated from the fuselage.
Post-Separation Actions
The pilot-in-command recovered engine power, synchronized it with the main rotor, and continued the approach to the grass strip at EPDE Dęblin. The landing was uneventful, and the crew sustained no injuries. The flight was conducted under day VFR.
Damage Assessment
After shutdown, the crew inspected the helicopter and found:
- Damage to the left fuselage near the fuel filler
- Impact marks on the left skid cross tube
- Impact marks on the left horizontal stabilizer
- Destroyed position light
- The left door was found 922 meters from the grass strip threshold and 1,130 meters from the touchdown point.
Cause and Contributing Factors
The investigation determined the cause of the door detachment: corroded safety pins that were intended to secure the door from sliding out of the hinges. The helicopter's Flight Manual (sections 9, 10, 11) permits opening the door during flight, which was a contributing factor to the incident.
Preventive Measures
The operator took the following actions:
- Conducted a detailed briefing of the incident with instructors, civil and military students, and technical personnel, emphasizing crew focus and procedures for a door loss during flight.
- Contacted Helicopters Guimbal (the manufacturer) to develop a repair bulletin for a complete repair.
- The manufacturer issued Service Bulletin SB 14-005A, requiring replacement of hinges with a version without additional safety pins, and repair of the left door and other damage.
- The helicopter was grounded until a scheduled major overhaul (planned for Q2 2021), which would incorporate the service bulletin.
The Polish State Commission on Aircraft Accident Investigation accepted these preventive actions and issued no additional safety recommendations.