By Mike DeNardo

PHILADELPHIA (CBS) — Federal investigators have released a preliminary report into Friday’s helicopter crash in Medford, New Jersey that killed a country music star.

The National Transportation Safety Board says the helicopter pilot in the crash that killed country musician Troy Gentry was unable to control the helicopter’s rotor speed using the twist-grip throttle.

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In a preliminary report, the NTSB says several minutes after takeoff the pilot radioed that he could “roll” the grip, but that there was no increase in RPMs.

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The report says the pilot, 1000 feet up, decided to perform an emergency procedure called an autorotation — in which the rotor turns from upward airflow, without the engine.

Two flight instructors on the ground reported hearing a high-pitched “whine” from the aircraft before the fatal impact at the Flying W Airport in Medford.