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Giving evidence on the sixth day of a coronial inquest into the crash, independent investigator Andrew McGregor said a pilot could experience ‘‘surprise or startle factor’’ from unexpected turbulence while flying in mountainous terrain.
Mr McGregor is a key witness in the inquest into the deaths in the February 19 crash of student pilot James Patterson Gardner (18), of Queenstown, and instructor pilot Stephen Combe, of Wanaka.
Transport Accident Investigation Commission reports into two other Robinson accidents, both published after the 2015 crash, contained lessons that might have assisted the two men and the Robinson R44’s owner, Over The Top, he said.
They contained evidence that could encourage a ‘‘more conservative and precautionary approach’’ when flying an R44, even in relatively benign weather.
The R44, in which the pair had finished a training exercise in the upper Lochy River valley and were returning to Queenstown, might have been affected by an ‘‘abrupt gust’’ that momentarily increased the wind speed to 20 knots while the aircraft was flying at an estimated air speed of up to 114 knots.
That could have caught whoever was flying the aircraft ‘‘off guard’’, causing them to make the wrong control movements in response, he said.
The year after the crash, the Robinson Helicopter Company recommended 110 knots as the maximum air speed for flying in non-smooth air.
Mr McGregor’s evidence continued the inquest’s focus on the complex interrelationships between geography, weather conditions and aircraft speed, and the occurrence or otherwise of turbulence and low-gravity (low-G) conditions.
Last week, coroner Alexandra Cunninghame was told how a low-G situation - felt by an aircraft’s occupants as lightness or weightlessness - was a potential contributing factor to a rapid right roll, mast bump (a rotor blade striking the fuselage) and catastrophic in-flight break-up of Robinson helicopters.
Mr McGregor said practising low-G recovery techniques in Robinsons was banned because of safety concerns, yet the only alternative method of training pilots for such a situation, which was ground-based simulator training, did not exist.
At the time of the 2015 crash, ground-based ‘‘safety awareness training’’ about low-G and mast bump risk, which has been mandatory in the US since 1995, was not required in New Zealand.
There was ‘‘uncertainty and debate’’ among experienced Robinson instructors in New Zealand about the best way to counter a right roll caused by a low-G situation, he said.
The inquest ends tomorrow.