After detecting a low-frequency vibration, Maloney said: "We declared an emergency and lowered the aircraft down."
Some 150m up, they decided to try and land on a hill where a line of trees and fence surrounded a grassy clearing.
The aircraft tipped upwards and descended tail-first, rolling onto its side when it landed.
Local woman Wendy McCarthy noticed the helicopter flying low above her head as she walked across farmland at Weiti Station.
"I thought, 'Jeez, that's a pretty tidy-looking helicopter', but it wasn't going to be for long," she said.
"It flew down the middle of the farm and was sort of dipping from one side to the other.
"It went towards Stillwater and hovered there for a bit and then it sort of backed up and hovered again and then it went down."
She said it appeared to be about 25m up when it started to descend rapidly tail-first.
At first she saw either dust or smoke as the helicopter rolled and she was worried it might explode.
As she was calling emergency services the cockpit door opened and two men got out. "I think they were very lucky."
Maloney has some 11,500 flying hours under his belt and said he was well prepared for this sort of situation, as was Idelon. "We're both test pilots and there's no time to be scared."
The impact fractured a bone in Idelon's shoulder. Maloney suffered cuts and scrapes. "I dare say I'll have a few bruises tomorrow," he said.
Idelon was taken to North Shore Hospital as a precaution and Maloney stayed to load his prized helicopter on to a trailer and get it back to base for the post-mortem.
In May last year, Maloney was forced to ditch into the Waitemata Harbour after losing power in the same model of aircraft.
He and a crew member swam from the sinking wreckage but escaped unscathed. He said two crashes in two years did not reflect badly on his company, nor had it not put him off flying.
"It was the structure of the helicopter that prevented us from being injured. And it absorbed the energy, which is what it's designed to do.
"I think Norbert and I were fortunate to be in that aircraft."
Maloney's wife and company co-founder Leanne said Maloney was a "fantastic pilot" and she could not imagine him giving up flying.
Composite Helicopters and the Civil Aviation Authority are investigating.