The wreckage of famed test pilot Scott Crossfield's single-engine plane indicates it broke apart during a severe thunderstorm, according to a National Transportation Safety Board report.

Crossfield, who in the early 1950s was the first person to fly at twice the speed of sound, died April 19 while en route from Prattville, Ala., to his home in Manassas, Va., in his Cessna 210A.

The 84-year-old pilot was the only person aboard when the plane crashed into mountainous terrain in northern Georgia.

The NTSB report, released Thursday, said Crossfield checked in with Atlanta air traffic controllers and shortly after 11 a.m. asked to turn to the south because of bad storms in the region.

Radar contact was lost at 11:10 a.m. when the plane was at 5,500 feet, just after the plane entered a Level 6 thunderstorm, the severest type, the report said.

The Federal Aviation Administration says a Level 6 storm is characterized by high wind and severe turbulence.

According to the report, debris from the aircraft was found in two areas about a mile apart, with the main wreckage in a crater 4 feet deep.

"The wreckage distribution was consistent with a low-altitude in-flight breakup," the report said.

Limited damage to the tree canopy also showed the plane plunged nearly straight down, the report said.

Parts of the airframe, engine and propeller blades were taken to a local Department of Transportation accident reconstruction yard.

The report said investigators uncovered no mechanical or other problems with the plane that would have caused the crash.