On the afternoon of the 15th of June 2022, a light helicopter crashed near Gruyère Aérodrome in Switzerland. The Cabri G2, produced by Hélicoptères Guimbal, is a two-seater helicopter powered by a reciprocating (piston) engine. The helicopter, built in 2013, was owned and operated by Swiss Helicopter AG under the registration HB-ZDQ. The first two minutes of this video show the helicopter at Gruyére.

Switzerland is interesting in that regard. All aircraft registrations start with a letter or code that specifies the country of registration: N in the US, G in the UK and HB in Switzerland. But the Swiss registrations use the next letter in the registration to specify the aircraft category; for example, Swiss aircraft starting with a registration of HB-A are twin-engine turboprops and HB-B are hot air balloons and HB-Z, as in this case, is for helicopters. Although actually, HB-A has recently been expanded as they ran out of room in HB-I and HB-J for jets, and now an Embraer E190-E2 has been filed under HB-A along with a dozen other Helvetic aircraft. The logic is that A was the only other letter that was used for commercial aircraft.

Back to HB-ZDQ. On that day, the helicopter was taken out for a private flight by a 65-year-old pilot (I love how the press never mentions the age of the pilots unless they are over 50) with a 70-year-old passenger. The pleasure flight was booked from Gruyère Aérodrome (LSGT) under Visual Flight Rules.

After start-up, the helicopter lifted off and suddenly began rotating around its yaw axis, spinning like an out-of-control fairground ride.

The pilot attempted to regain control of the helicopter in order to land. The helicopter continued to roll and bank before crashing “several tens of metres” into the field east of the runway.

Epagny FR – Bei Vergnügungsflug mit Helikopter abgestürzthttps://t.co/lb7FsN0vhP pic.twitter.com/xuZ0d2Utcq

— POLIZEI-SCHWEIZ.CH (@POLIZEI_SCHWEIZ) June 15, 2022

The passenger suffered severe injuries. The helicopter was badly damaged and likely a write-off. But amazingly, they managed to land on the skids. Both the pilot and the passenger survived the crash, which the police described as a miracle.

The airport was closed after the accident but was able to open the following morning after the wreckage was removed from the field.

Someone standing near the runway quickly began filming as the helicopter swerved through the sky. I found a copy on the Heliponti BR Facebook group. Watching the video, I’m even more amazed that the two occupants survived.

When the video first appeared on social media, many were convinced that it must be a radio-controlled model.

In an odd coincidence, Flyer featured the same helicopter in an accident analysis just a few weeks ago; they appear not to have known about this incident the month before.

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While looking for more information, I found another helicopter incident which took place in France in 2020 that, on the surface at least, looked quite similar. In this case, the pilot and five passengers were in an Aerospatiale AS350 which had stopped to refuel. The passengers rearranged to allow a new passenger to sit in the front. The helicopter had dual controls and the pilot advised the passenger not to touch the controls, especially the cyclic pitch control. However, he did not mention the pedals and he had no visibility of her feet. They had just entered the hover when the helicopter began turning rapidly around its yaw axis. The pilot could not stop the rotation but managed to land on the skids with a bounce. Afterwards, no fault with the helicopter could be found. The BEA concluded that the pilot did not input enough right pedal during hover and, as a contributing factor, that the passenger’s feet may have been in the way, hampering or preventing the movement of the pedals.

This may not be relevant, although I note that the Cabri G2 also has dual controls. Still, the report points out that unanticipated yaw at low speed as a flight characteristic of single rotor helicopters has been the subject of two Safety Information Notices by Airbus Helicopters.

Where this type of unanticipated yaw situation is encountered, it may be rapid and most often will be in the opposite direction of the rotation of the main rotor blades (i.e. right yaw where the blades rotate counterclockwise). Swift corrective action is needed in response otherwise loss of control and possible accident may result.

However, use of the rudder pedal in the first instance may not cause the yaw to immediately subside, thus causing the pilot to make inadequate use of the pedal to correct the situation because he suspects that it is ineffective when, in fact, thrust capability of the tail rotor available to him remains undiminished. “Loss of tail rotor effectiveness” is not, therefore, a most efficient description as it wrongly implies that tail rotor efficiency is reduced in certain conditions.

The Swiss Transportation Safety Investigation Board (STSB) is investigating the crash of the Cabri G2 at Gruyére and I’m sure we will soon hear more on the cause(s) of this remarkable accident. You can find their preliminary report in PDF format in German and French.