The Eurocopter AS32, part of Fly Precision's fleet, went down just before 3 p.m. PT in Mariposa County as it supplied water drops to crews battling the Dome Fire.
The Dome Fire, which ignited on September 15, has already consumed more than 3,000 acres in the park and grew by 283 acres overnight, leaving 15 % containment.
Federal Aviation Administration data confirms the aircraft carried two crew members, both of whom were killed. The NTSB and FAA are investigating, with the agency saying investigators will visit when fire conditions allow and a preliminary report is expected within 30 days.
Forest Service spokesperson Adrienne Freeman said the crew were contracted to the Price Valley Rappel Crew in Idaho. Fly Precision released a statement expressing grief and asking for privacy for families.
A local volunteer who had been coordinating water drops for two weeks said the loss will be felt deeply by the firefighting community.