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The Australian aviation watchdog has urged all operators of Robinson R22 helicopters to watch for cracking in the main rotor blade.
It follows all Robinson helicopters being placed on a New Zealand watchlist in October, which prompted swift reactions from three Government organisations.
On December 23 the Civil Aviation Safety Authority (CASA) - Australia's version of the Civil Aviation Authority - published an airworthiness bulletin following a ``significant main rotor blade cracking event'' recently reported on an R22 Beta II helicopter, fitted with A016-6 main rotor blades.
The bulletin said during low-level operations at slow airspeed the pilot experienced an ``unusual increase in vibration levels'' and began a landing.
``Shortly before making a successful landing and whilst in the hover the pilot reported an increase in vertical vibration levels and a decrease in power available.
``Subsequent inspection revealed a crack approximately 160mm in length, emanating from the trailing edge ...''
There was evidence of ``very minor'' corrosion near the crack.
The alert said the blade had been in service for 1782.7 hours. The manufacturer stipulates a life limit of 2200 hours, or 12 years.
``Robinson Helicopter Company will soon be issuing a Safety Alert on the reported findings to date.
``The blade is currently being investigated by the ATSB (Australian Transport Safety Bureau), however, at this stage details are limited, with the root cause yet to be determined.''
CASA ``highly recommends'' when carrying out the main rotor blade inspection operators pay ``particular attention ... to the main rotor blade trailing edges''.
``CASA also advises that following sudden and increased vibration levels that the pilot of the aircraft land immediately to investigate the cause.
``Increased vibration levels should be reason to initially suspect a cracked blade.''
Robinson aircraft were placed on the Transport Accident Investigation Commission (TAIC) watchlist in October. Commissioner Stephen Davies Howard said about 300 Robinson helicopters were registered in New Zealand, comprising about 40% of the total helicopter fleet.
Since 1996 the commission had investigated 14 ``mast bumping'' accidents involving Robinsons, resulting in the deaths of 18 people.
They included Over the Top pilot Stephen Anthony Nicholson Combe (42), of Wanaka, and James Louis Patterson Gardner (18), of Queenstown, who were killed when the Robinson R44 helicopter they were flying in crashed in the Lochy River valley, southwest of Queenstown, on March 18, 2015.
Mast bump is contact between an inner part of a main rotor blade or a rotor hub and the main rotor drive shaft or ``mast''.
The outcome was usually catastrophic, Mr Davies Howard said.
The commission had also identified that the rate of Robinson helicopter in-flight break-ups accidents in New Zealand had not been significantly reduced by the adoption of US Federal Aviation Administration measures intended to help prevent such accidents.
Further, the format of the Robinson flight manuals and terminology did not draw enough attention to safety critical instructions and conditions that could result in serious injury or death.
``Four of our earlier recommendations made as a result of Robinson mast bump accidents have yet to be actioned.
``We therefore remain concerned that there is a real risk that we will see more of this type of accident,'' he said at the time.
Within five days of that announcement, the Department of Conservation banned its personnel from using the aircraft, Tourism New Zealand effectively did the same and TVNZ reminded staff if Robinsons were offered as a flight option, that offer should be ``flatly refused''.