ESTES PARK, Colo. -- An overheated engine that "melted away" its own steel turbine led to the fatal crash of a firefighting helicopter last week, investigators said.

National Transportation Safety Board investigators were still trying to determine what caused the overheating.

NTSB experts found the burned-out turbine during their examination of the helicopter, which crashed July 30 while making water drops on a 4,413-acre fire near Estes Park.

Pilot Gordon Knight, 52, died in the crash.

"Witnesses reported hearing a high-pitched whine and seeing rotor blades turning slowly, so we suspected a problem with the power train," said Arnold Scott, chief investigator for the Denver office of the NTSB.

BIG ELK FIRE INTERACTIVE ARTICLE: Plane In Previous Crash Owned By Same Company VIDEO: Eyewitnesses Describe Crash VIDEO: Working Life Of Tanker Pilots VIDEO: Role Of Air Tankers VIDEO: Evacuee Tells His Story SLIDESHOW: Air Tanker Overview SLIDESHOW: Big Elk Fire - Day 1 SLIDESHOW: Big Elk Fire - Day 2 Big Elk Fire Map FLASH: Fire Causes And Protections DISCUSSION: Should Old Planes Still Be Used? RESOURCES Evacuation Tips Smell Smoke? MAP:Fire Point Of Origin USFS: Big Elk Fire Larimer County Web Site Current Colorado Wildfires Clickable Colorado Wildfires Map

Federal Aviation Administration investigators examined maintenance records for the Aerospatiale SA-315B Lama helicopter, which was owned by Geo-Seis of Fort Collins. The rebuilt engine on the 1978 helicopter had logged only about 200 hours of flying time.

"We suspected there was a power problem of some sort," Scott said Monday. "We disassembled the engine, and the whole turbine section after the combustion chamber is just literally toast, just burned up."

When the turbine burned out, it interrupted the transfer of power from the helicopter's jet engine to the rotor blades, Scott said.

"It's like going down the highway at 60 miles an hour in a standard-shift car and, without taking your foot off the accelerator, pushing in on the clutch. Your engine overspeeds but you have no power being developed," he said.

The engine's temperature exceeded what the turbine was designed to withstand.

The water-dropping helicopter was leased to the city of Boulder and Boulder County and stationed at the Boulder Municipal Airport. It was manufactured by the same French company that builds the Concorde airliner.

According to NTSB reports, the Lama 315B model has had seven crashes in the United States since 1995. There were no fatalities and five injuries in those crashes.

The reports list a variety of causes for the crashes: two ran out of fuel, two experienced loss of power, two reported a popping sound prior to crash and one was a ground crew error.

Knight had been filling up the chopper up with water at the Big Elk Meadows Reservoir, making water drops on the hot spots and patrolling the burn area when he made a desperate radio call, telling dispatchers that his chopper was going down, 7NEWS reported.

Fire crews mopping up and lighting back fires just north of the fire witnessed the crash, but it took them more than an hour to hike to the rugged, deeply forested crash scene, 7NEWS reported.

The fatal chopper crash occurred 11 days after two air tanker pilots were killed fighting the same fire.