Serious incident Guimbal Cabri G2 HB-ZPU,
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ASN Wikibase Occurrence # 268409
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Date:Saturday 26 June 2021
Time:09:55 LT
Type:Silhouette image of generic G2CA model; specific model in this crash may look slightly different    
Guimbal Cabri G2
Owner/operator:Air Evolution
Registration: HB-ZPU
MSN: 1276
Fatalities:Fatalities: 0 / Occupants:
Aircraft damage: None
Category:Serious incident
Location:Bola, Lostallo -   Switzerland
Phase: En route
Departure airport:Lodrino (LSXR)
Destination airport:Lodrino (LSXR)
Investigating agency: STSB
Confidence Rating: Information verified through data from accident investigation authorities
The Guimbal Cabri G2 helicopter, registered as HB-ZPU, entered service at the beginning of 2021 at Air Evolution Ltd. and was used primarily for pilot training.
Crews noticed from the beginning that, when starting the engine and in normal operation, the oil pressure was always displayed within the permitted range, but at its upper end.
As part of the first 100 hours inspection after the aircraft entered service, the aircraft maintenance company reduced the oil pressure by approximately 0.6 bar, in accordance with the engine manufacturer's specifications.
In the subsequent test run on the ground, the oil pressure was displayed in the centre of the permitted range on the gauge. The helicopter then re-entered service.
On the morning of 26 June 2021 the crew, consisting of a flight instructor and a trainee pilot, met to prepare a training flight. On the programme for the flying lesson were the introduction of navigation, and off-field landings in the Misox area. This was the first flight after the 100 hours inspection.
After approximately 45 minutes’ flying time, during which a range of exercises and one off-field landing at Soazza had been performed, the crew decided to set off on the flight back to Lodrino.
As the helicopter was flying at an altitude of approximately 2,500 ft AMSL, cruising above Lostallo, the clutch light flickered on. After a further approximately 10 seconds, during which the flight instructor also noticed yaw movement by the helicopter and drop in the main rotor speed, a so called needle split,2 the clutch light remained steady on. In response, the flight instructor commenced an autorotation to a suitable field. When levelling off and performing a flare with power recovery, the flight instructor once again notice a needle split, in which the speed of the main rotor dropped to the bottom of the permitted operating range in relation to engine output.
In this phase the crew heard grinding noises from the drive belt, as are also typical when starting this type of helicopter.
The helicopter then touched down without incident, but the lack of RRPM meant that the pilot was no longer able to apply full engine power and it became impossible to continue the flight.

The subsequent investigation showed a narrowed section, as well as chips and non-deburred drilling work in one of the oil ducts in the accessory housing. An inspection of further engines constructed in 2020 and 2021 revealed similar findings.



Revision history:

08-Oct-2021 07:49 harro Added

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