"It is a sensor that 'measures' disturbances in the earth's magnetic field caused by large mineral deposits. An aircraft the size of a Bell 206 has enough ferrous material in it to show up and be 'seen' by one of these machines,'' Mr Booij said.
He dismissed media reports that the helicopter had been flying in dangerous conditions.
"The conditions at the time the helicopter went missing were believed to be low cloud with reduced visibility but still favourable for flying, thereby allowing the flight to depart."
Hevilift spokesman Colin Seymour told APNZ yesterday the search area was mountainous and rugged, and covered in dense jungle.
He said it was still being treated as a search and rescue mission rather than a recovery operation.
"We're still hopeful, we remain hopeful and that's where we are focussing our energies just on finding these guys."
New Zealand Defence Force Papua New Guinea advisor Lieutenant Colonel Richard Taylor said on Sunday that search teams had a very "difficult task" ahead of them.
He said often with helicopter crashes the blades "sheared off" and the wreckage fell into the dense jungle canopy, making it very difficult to find.
Ten years ago, Mr Annan's brother Matthew was killed in a topdressing plane crash in Australia, Central Otago Flying Club president Russell Anderson said.
He had known the family when they lived in Alexandra.
"It's cliche I know, but no parent should have to bury their children and some families unfortunately, it's the way the cards get stacked against them unfortunately."
Flying ran in the family, as Mr Annan's late father, Bill, was president of the Central Otago Flying Club for more than six years. He was also made a life member of the club.
Mr Anderson today said his hairs pricked up on Saturday when he heard news a New Zealander was one of those on the missing helicopter.
"I know quite a few pilots, it being an aeroclub, there's a lot of Alexandra lads who have gone on to be rotary wing pilots around the world.''
"Your heart goes out because of the not knowing and the waiting and the ripple effect through the whole community, both countries, Australia and New Zealand."
Mr Anderson said he knew the whole Annan family, including Mr Annan's step-mother who lived in Alexandra.
Mr Annan, who lived with his partner in Australia, had been flying for about 30 years and was a very experienced pilot.
"He'll be very well respected within the organisation, the community, the flying fraternity, his wealth of experience."
Mr Anderson was sure everything was being done to find Mr Annan and his colleagues, but knew it was "nasty terrain" to be searching in.
"In our heart of hearts we all hope for a miracle, and that there's closure very soon for the family, because the waiting must be diabolical. I couldn't imagine what that would be like."
