The main rotor came off a medical helicopter before the craft crashed into a southeast Indiana farm field, killing three crew members, authorities said Tuesday.

Decatur County Sheriff Daryl Templeton and National Transportation Safety Board spokesman Peter Knudson told The Associated Press that crews found rotor parts hundreds of yards away from the fuselage after the crash Sunday.

"The rotor blades were separated and came to rest about 200 yards away," as did the rotor mast, Knudson said. "We have witness reports reporting the same thing."

Templeton said investigators found the rotor blades 320 yards from the rest of the wreckage.

It was the second fatal crash in Indiana in 4 1/2 years for the company that operated the helicopter, Missouri-based Air Evac Lifeteam.

Witnesses told investigators that the helicopter's nose tipped down before it crashed and exploded in the field near the town of Burney, about 40 miles southeast of Indianapolis.

"Much of the fuselage was burned pretty considerably," Knudson said.

The NTSB is not expected to release the official cause of the crash for at least nine months, Knudson said.

The fuselage was found 1.2 miles from where the helicopter took off from the Burney Volunteer Fire Department, Knudson said.

The helicopter was not carrying a patient when it crashed.

It had been at an event for the fire department and crashed as it was returning to its base in nearby Rushville.

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• Indiana Medical Helicopter Explodes in Crash; 3 Killed