A helicopter rapidly descended before smashing into the ground and killing two occupants in the Snowy Mountains, crash investigators have found.
The Bell LongRanger chopper crashed on the afternoon of April 3 in the sparsely populated Kiandra Flats area of Kosciuszko National Park in NSW.
The 64-year-old woman and 75-year-old man from Sydney's northern suburbs on board were fatally injured by the impact.
The helicopter had made a steep left descending turn from 2256 metres after taking off in poor weather, according to the Australian Transport Safety Bureau's preliminary report released on Friday.
It had departed the Canberra suburb of Majura as part of a flying tour of seven helicopters. The aircraft were on a shared itinerary but could travel independently, the report notes.
As the weather deteriorated, six of the helicopters landed at a property at Wee Jasper to the northeast of Canberra, while the fated helicopter travelled south, landing on Long Plain Road in the Brindabella region.
When the seventh helicopter failed to arrive at Wee Jasper, the other pilots contacted authorities who began a search, however this was called off when the pilot reached mobile reception.
Close to four hours after landing at Long Plain Road just before 3pm, the pilot took off again, according to recorded flight tracker data.
Police officers sent to look for the helicopter saw the craft flying low to the south through rainy, overcast conditions, the bureau's director of transport safety Stuart Macleod said.
About 10 minutes into their second flight, the pilot turned towards Tumut, which was their refuelling site.
The report shows the helicopter began to climb for about six minutes, reaching about 2134m above sea level, before it descended to 2073m, then climbed again, to a height of 2255m.
"After climbing to (2255m) the helicopter commenced the steep turn," Mr Macleod said.
"Its ground speed increased to (246 km/h), and its descent rate exceeded (1158m) per minute," Mr Macleod said.
The helicopter hit the ground at 3.36pm, in an area covered in grass and protruding rocks.
A search began the following morning after the man and woman failed to meet with their tour group.
The craft was located at the accident site that evening.
The ATSB said they have not found evidence of defects with the helicopter's drive train or flight controls, nor any suggestion of an in-flight break-up.
Further investigation will analyse the pilot's maintenance, witness information and pieces of the helicopter recovered from the site.
A final report will be published in the future.
