- The ATSB recommends owners of CH-7B series helicopters ensure the integrity of the stabiliser before flying.
The ATSB is investigating a second fatal accident involving in‑flight separation of the stabiliser, and subsequent loss of control, involving Cicaré CH-7B helicopters.
Preliminary technical examination at the ATSB’s facilities in Canberra, indicates that in both instances the stabiliser failed due to cracking associated with metal fatigue. In the most recent accident, the crack propagated in a circumferential manner through approximately 75 per cent of the welded structure prior to failure.
While the ATSB is working to establish the factors leading to the two failures, owners are advised to exercise extreme caution in the operation of their helicopters.
The examination showed cracking in the stabiliser attachment outboard of the tail boom, coincident with the welded intersection of the conical and tubular sections of the attachment. The location of the cracking in the attachment cannot be easily inspected as they are obscured by the upper and lower vertical stabiliser fairings.
Stabiliser attachment failure location
The cracking is unlikely to be easily visible during inspection. However, black dust in the vicinity of the attachment bracket, and working rivets are indicative of increasing stabiliser movement as the crack develops.
The ATSB is working to establish the origin of the failure. However, initial indications are that the fatigue cracking occurred after as little as 100 hours of operation and may be associated with aerial stock mustering. Additionally, in the first accident, operation of the helicopter with a high level of vibration may have been a factor.
CH‑7Bt tail section showing the location of fatigue fracture on the stabiliser attachment
Fractured stabiliser attachment bracket with black dust outlined in white (in two places)
Typical indication of ‘working’ rivets (photograph not of a CH-7B helicopter)
The ATSB recommends that owners of CH-7B series helicopters ensure the integrity of the stabiliser prior to further operation and on an ongoing basis. While the ATSB is working to establish the factors leading to the two failures, owners are advised to exercise extreme caution in the operation of their helicopters.
Cicaré has advised that if any doubt arises concerning the inspection or maintenance of any part, piece or component, their technical department should be immediately consulted.
In addition, owners may wish to discuss any concerns with an appropriately‑licenced aircraft maintenance engineer, the Sport Aircraft Association of Australia or with the Civil Aviation Safety Authority before further flight.
If you find any cracks in the stabiliser attachment, please call us on 1800 020 616 or email ATSBinfo@atsb.gov.au.