The dive teams are at the limit of their resources in the deep-water search and may require the help of a commercial operator should a retrieval be required.
Joint team leaders Lieutenant Commander Andrew McMillan and Senior Sergeant Bruce Adams say the exercise is "extremely challenging" because of the environment, steeply sloping underwater terrain and the lake's altitude.
It would be a slow and thorough search but uppermost in their minds was to achieve a result for the family, the dive team leaders said.
Their primary task yesterday was to find the wreckage, which is believed to be lying on a ledge about 80m down.
"This is not a recovery mission. We don't know exactly where it [the helicopter] is," Lt-cmdr McMillan said.
A side-scan sonar search of the lake bottom under the spot where an oil slick was marked on Sunday has revealed items of interest to the search teams but the dive team leaders and Sgt Aaron Nicholson, of Wanaka, said nothing could be determined until a closer look was taken using a remotely operated camera.
The sonar could pick up shadows from large pieces of machinery, such as a transmission or other mechanical pieces, but the shadows could equally turn out to be rocks, Lt-cmdr McMillan said.
If close-up photographs confirmed the items were from the helicopter, the dive teams would then turn their minds to the retrieval operation, which was important for the Saxton family and to the Civil Aviation Authority, which is investigating why the machine crashed, he said.
But while photographs could be obtained down to 300m, a diver could not be sent down 80m and hook on a cable so the items can be winched up - divers could only go down less than 50m, a constriction worsened by the lake's altitude.
Another option will be to use a remotely operated vehicle with a manipulator or arm that can fix a hook to any items resting on the bottom of the lake, but the Navy does not have that equipment in Wanaka.
Experienced search and salvage diver Mike Baker, of Picton, said when contacted by the Otago Daily Times such equipment was available in New Zealand.
He said using a manipulator was reasonably straightforward and the safest option.
All the evidence collected by searchers since Saturday supports the belief Mr Saxton's helicopter lies about 80m beneath Lake Wanaka, 200m from the eastern shore of Lake Wanaka, north of Mou Waho Island.
Mr Saxton went missing on Saturday evening during a repositioning flight in his helicopter to prepare for vineyard frost-fighting the next day.
His father, Dave Saxton, was flying the same trip in another helicopter and reported his son missing when he did not arrive at Wanaka Airport.
A few items, including a fuel tank, helmet, aircraft cover, manuals, a jacket and a backpack were salvaged from the lake and shoreline on Sunday but no further wreckage has been found since.
Searchers marked an oil slick above the accident site with a buoy on Sunday morning but they discovered yesterday the buoy had sunk after two days of 1.5m swells at the site.
Yesterday's sonar scanning exercise began at 4am and was called off about 11am because of rough conditions.
It was due to recommence last night.
The costs of the search are being borne by Government agencies, including the police, Rescue co-ordination Centre and the Navy.
Lt-cmdr McMillan said it was "impossible to put a dollar figure" on it.
The environment dictated why the teams had brought so much gear and so many divers, he said.
The search
A joint Navy and police search for Morgan Saxton and his helicopter may take several days. Items of interest found in sonar scans of the crash site yesterday will be examined again using a remotely operated vehicle containing a camera. High winds halted the operation yesterday. More sonar scans were due to be carried out last night if the wind dropped. A retrieval operation would be "extremely challenging". The divers are at the limit of their resources and may require assistance from a commercial operator.
