It has been a ''bad and very sad year already'' for aviation in the South, the Civil Aviation Authority says.
Two senior safety investigators arrived at the scene of a downed Cessna 185 near Wanaka last night to piece together Monday's crash, which killed Christchurch couple Paul Clifford William Macdonald (50) and Emma Kate Macdonald (43) and their two children, Georgina Emma (7) and Benjamin Paul (5).
''It is too early to speculate on what has happened,'' Civil Aviation Authority spokesman Mike Richards said.
''There are literally hundreds and hundreds of possible variables that need to be explored.''
The deaths raised to six the number of aviation fatalities in Otago and Southland so far this year, after the deaths of Stephen Combe and James Patterson-Gardner in a helicopter crash in the Lochy River Basin, near Queenstown, last month.
''With the latest accident claiming four lives it makes 2015 a bad and very sad year already,'' Mr Richards said.
Otago Lakes-Central area commander Inspector Olaf Jensen said police were notified of the crash about 12.40pm on Monday and a Wanaka LandSAR team recovered the four bodies from the plane's wreckage later that day.
It appeared the family left Wanaka Airport about 11am on Monday destined for the Skippers area, he said.
The plane crashed near the north branch of the Motatapu River, at an altitude of 1200m, about 15 minutes' flying time from Wanaka.
Mr Richards said the safety investigators had been briefed by police and viewed photographs of the scene before flying to the accident site by helicopter.
''We already know the accident has two distinct areas of impact - one on the ridge-line and another lower down the mountainside, which is where the Cessna 185 came to rest,'' he said.
''It is a complex task and each member of the investigation team, which includes an air force assistant, will need to be pre-harnessed and use dive ropes to be safely lowered down to the site of the wreckage.''
The investigators were expected to spend about three hours at the scene last night. Mountain guides were on hand to assist them with their gear.
''This is rugged and unforgiving terrain and we have to make sure that the investigation team gets to cover as much ground as quickly and safely as possible,'' he said.
Once the investigators completed their site work, the wreckage would be removed and taken to a secure storage facility in Wanaka or Queenstown.
It was likely the engine would be taken to a workshop in Dunedin to see if there were any mechanical issues which might have contributed to the accident, he said.
The Civil Aviation Authority investigated 10 crashes last year in Otago and Southland.
The Macdonald family's deaths have been referred to the coroner.
