The proposed loan will have no impact on rates, NRC says.
NEST would be required to pay back the loan over five years, and the trust would be required to forward any extraordinary charitable donations of more than $100,000 to the council, to be applied to the principal balance of the loan.
The council had supported the rescue helicopter through a targeted rate for the past eight years, but currently provided the trust with $525,000 a year from the emergency-services contestable fund.
NEST has found two Sikorsky S-76C helicopters suitable to replace two of its existing ones.
The existing helicopters need replacing as the airframes are getting old and maintenance costs are climbing.
NEST said having newer helicopters would mean having access to the latest technology and avionics and the opportunity to get more horsepower, which meant a longer range.
The new helicopters will not cut the maintenance costs to zero, but they will come down slightly.
If the loan proposal went through, the trust will carry out a fundraising campaign to repay the council.
NEST chairman Paul Ahlers would not reveal where the new choppers were located nor the cost. "We're actually buying one machine and leasing one machine with an option to purchase."
Mr Ahlers said the trust had an annual maintenance budget of $2.3 million.
"We had planned to do this in the next three to five years but the opportunity came up now," he said.
Initially NEST had looked at commercial bank lending rates, but after it informed the trust's main supporters of its plans, the council offered to help.
"If it doesn't go in our favour, we would pursue other options. We sincerely believe this opportunity is too good to miss," Mr Ahlers said.