The navy hopes to send an underwater robot to the bottom of Lake Sumner in North Canterbury on Friday in the search for a crashed helicopter and its pilot.
Police believe they know where Michael Mehrtens crashed on Monday afternoon, and have sought navy assistance to reach the wreckage.
Police say at 125 metres, the lake is too deep for police divers to reach the helicopter.
The plan is for the robot to attach airbags to the aircraft to allow it to be towed to shallower water so that divers can check inside it for signs of the pilot.
The Civil Aviation Authority will investigate the crash and one of its investigators will be at the lake on Friday.
Michael Mehrtens' helicopter went down in fine weather while he was spraying for gorse over Department of Conservation land.