"I was a very angry man after the crash and the only way to make the anger go away was to get back in the air," Hartley said.
In 1988 and following Hartley's move to Ruatoria on the East Coast, Cyclone Bola hit and isolated many of the coastal communities. At the onset of the storm Hartley rescued people from rooftops and submerged cars, collected patients needing medical attention and lifted people to higher ground.
"All the flying resulted in an almost empty fuel tank and, with no fuel delivery available, I took up an offer from the naval ship HMNZS to refuel from where it was sheltering off the East Cape. Landing on a pitching deck in cyclonic conditions was certainly exciting."
While on the coast, Hartley established the East Cape Rescue Trust, the first community-owned rescue helicopter service that is still operational today as the Eastland Rescue Helicopter Trust.
"After Bola I spoke on Radio Ngati Porou about the part helicopters played in the disaster and, by the end of my time on air, people had spontaneously donated $6300 and the rescue helicopter was established," Hartley said.
He also worked with rescue squads linked to the First Response Fire Brigade in each community from Tolaga Bay through to Opotiki, training them in rescue techniques.
Hartley was also smack-bang in the centre of the Ruatoria Rastafarian movement when, from 1985 to 1990, "Rastas" burned more than 30 local buildings as part of their mission to return local land to the original Ngati Porou owners.
"Although I loved my time on the coast, the good and the bad, I found picking up the pieces as a rescue pilot was soul-destroying. My saddest rescue was picking up two young children badly injured in a crash and having to leave four others on the ground knowing they were in a bad way."
Hartley has always loved precision flying which eventually led to the work he and his company currently carry out – mainly in China. He pioneered live-line, human sling maintenance and insulator washing by helicopter in New Zealand and went on to introduce the procedure to China and India.
Most of his work is now in China, where Hartley senior lectures while his son Wayne pilots.
Hartley's wife Jacqueline says there is one thing her father (who was also a pilot) told her about her then-to-be husband.
"He said to me that flying was infectious and that Denis had one of the worst cases he had ever seen."
But ask Hartley and he maintains flying is all about the feeling of freedom.
"There is nothing more incredible that being up in the air on a crisp, early morning."
