Accident to the Guimbal Cabri G2 registered F-HGRE on 18/02/2022 at Grenoble-Isère AD
Perte de contrôle en translation, collision avec un poteau en instruction solo
When the student-pilot joined the long final for Grenoble-Isère airport, the aerological conditions were changing. The wind was picking up and changing direction, and this was accompanied by turbulence and strong gusts. These gusts were not forecast for the flight window in the morning’s TAF message.
When hover taxiing to the parking point, with a crosswind from the right, the helicopter started to turn on its yaw axis to the left. The student-pilot initially applied right rudder without reaching the stop, but was unable to counteract the movement. The left yaw rotation was then accentuated by the pilot pulling on the collective pitch lever to get away from the ground, then by the left rudder input made by the pilot, who was probably disoriented by the high yaw rate. After several turns, the helicopter collided with a pylon and fell vertically to the ground.
The BEA issues 1 safety recommendation:
- Recommendations FRAN-2023-004 / Improvments to Cabri G2 yaw control training:
The design of the Cabri G2 equipped with a Fenestron has specific impacts on the yaw control of this helicopter, which requires pilots to be more reactive in their rudder pedal inputs. Inexperienced pilots and/or pilots used to conventional tail rotors need to be particularly vigilant.
The analysis of Cabri G2 accidents shows that more than half of these accidents concern losses of yaw control. These losses of yaw control are mostly the result of:
- inadequate management of exercises in instruction, leading to a drop in rotor speed that has a direct influence on the effectiveness of the Fenestron, and therefore on rudder pedal input;
- an input of insufficient amplitude and/or rapidity on the right rudder pedal in the event of an unplanned departure in yaw to the left.
The subject of controllability in yaw is covered by Guimbal in three Service Letters (SL) pertaining to specific flight situations (approach, simulated engine failure, low rotor speed). In addition, Guimbal has incorporated this subject in a training session for instructors and offered to operators. The FHATO Flight Training Center instructors did not know about the Service Letters and did not attend the training session.
Yaw control in approach is also mentioned in the OSD for Flight Crew for the Guimbal Cabri G2 as a specific training topic that must be given specific focus by training organisations. However, the OSD refers to the Guimbal Service Letters which describe the phenomenon but does not indicate how to teach this phenomenon as part of theoretical and practical training. The investigation highlighted the need for more specific information to establish a theoretical and practical instruction program on the topic.
The FFH’s Cabri G2 training programme model approved by the DSAC does not expand on the information in the OSD. The specifics of the Fenestron and their consequences on yaw control of the helicopter were, however, identified in 2017 as risk factors by the DGAC, which identified insufficient pilot knowledge of the topic.
Consequently, the BEA recommends that:
- whereas the number of Cabri G2 accidents linked to a loss of yaw control and their proportion with respect to the total number of accidents;
- whereas the sometimes inadequate or non-existent training of pilots on the specifics of the Fenestron and their consequences on manoeuvrability in yaw control;
- in the absence of specifications in the Cabri G2 OSD on how to teach the specifics of yaw control in instruction;
- whereas all of the measures taken by Hélicoptères Guimbal for the training of instructors and pilots on the Cabri G2;
- whereas some of these measures could only concern French training organisations;
- whereas the ATO concerned by this accident had no knowledge of the training for instructors proposed by Hélicoptères Guimbal that was introduced in 2020;
- whereas the need to assist training organisations with improving theoretical and practical training programmes and developing the associated training materials;
Hélicoptères Guimbal provide all training organisations with further information or recommendations on how to teach yaw control on the Cabri G2 as part of theoretical and practical training.
The recommendation is being processed
The status of the recommendations is available at SRIS2: click here
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Note: in accordance with the provisions of Article 17.3 of Regulation No 996/2010 of the European Parliament and of the Council of 20 October 2010 on the investigation and prevention of accidents and incidents in civil aviation, a safety recommendation in no case creates a presumption of fault or liability in an accident, serious incident or incident. The recipients of safety recommendations report to the issuing authority in charge of safety investigations, on the measures taken or being studied for their implementation, as provided for in Article 18 of the aforementioned regulation.