CHATSWORTH, Ga. (AP) — Federal investigators who examined the wreckage of a small airplane crash that killed four people earlier this month in Georgia concluded that the aircraft broke apart in midair after flying into a thunderstorm.

The National Transportation Safety Board released a preliminary report Tuesday into the July 1 crash, which occurred in Murray County, about 90 miles (145 kilometers) northwest of Atlanta. The agency concluded the plane "was destroyed during an inflight breakup" and said witnesses were watching a thunderstorm overhead when the crash occurred.

"As they continued to watch the thunderstorm they heard a loud 'boom' followed by observing pieces of the airplane and personal belongings falling out of the clouds," the NTSB report said.

The crash killed the pilot, 55-year-old Dexter Lee Gresham, and his wife, 61-year-old Mary Jo Yarbrough. The couple lived in Etowah, Tennessee. Yarbrough's two grandchildren also died. They were identified as Austin Day and Kinsley Wilson. The children, both 10, were a brother and sister who lived in Corinth, Mississippi.

The NTSB said the family members were heading home from a weeklong trip when they took off from Tuskegee, Alabama, en route to Athens, Tennessee.

Radar data showed an aircraft consistent with the time and direction of Gresham's plane traveling northeast over Georgia when it encountered an advancing thunderstorm, the report said. Radar contact with the plane was lost after it entered the storm.

Debris from the Piper PA-23-250 aircraft was scattered along a 1-mile (1.6-kilometer) path, the report said. The plane's cockpit, fuselage and engines were destroyed.