You never know when you might need them. These heroes who risk their lives for members of the public.

As they cooled off under sunny skies in west Auckland's Cascade Falls, five able-bodied teenage schoolmates certainly weren't expecting to rely on the expertise of the Auckland Westpac Rescue Helicopter.

But as the weather suddenly turned, one of the boys, Denver Woolley, would soon be owing his life to his saviours in the chopper hovering above him.

Despite the force of the water, which swept the then 17-year-old downstream, Denver managed to swim to a ponga tree and wrap his arms around it.

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The first hero Denver saw was paramedic Russell Clark.

He was winched down by pilot Rob Arrowsmith, who hovered in driving rain and gusty wind at a height of 60m, during what he called a "pretty hair-raising" rescue.

As a frightened, shivering and fatigued Denver looked at him, Clark got a strop on him, and told him to hold on.

Little did Denver know at the time but he owes his life to a hero decision.

The rescue helicopter team, which included crewman Ati Wynyard, were convinced they were going to be looking for bodies and had to decide whether to use their last 10 minutes of fuel to do so.

If they had decided to get gas, they would have run out of daylight and Denver may not have lived to meet the trio last week and put names to the faces of his three heroes.

The dramatic incident is just one of more than 1000 missions the helicopter crew carries out a year.

And now it's the heroes turn to ask for help.

To continue their lifesaving work the crew need two new choppers.

The trust that runs the helicopters is only partially funded by the Government.

It also receives funding through the council's Auckland Regional Amenities Funding Board but to stay afloat, it needs corporate sponsorship - like through Westpac - and holds fundraising activities and appeals to members of the public.

But it's still $2.9 million shy of the funding for the helicopters.

The big donors (giving $10,000 or more) will get their family name on the tail section of one of the new helicopters.

But every donation counts.