A small plane that crashed last week in South Florida, killing all four people aboard, apparently spun into the ground and might have been overloaded, according to a National Transportation Safety Board preliminary report released Saturday.

The Cessna 172S was carrying four men weighing a total of 768 pounds, 40 pounds of baggage and a substantial load of fuel, the report said. The plane was permitted to hold up to 862 pounds in occupants, baggage and fuel.

Kemper Aviation co-owner Jeffrey Rozelle, who was the pilot, two Florida Atlantic University students and a bird expert were killed in the March 13 crash, which remains under investigation.

The crash came less than six months after two other fatal crashes involving planes owned by Kemper, a flight school. Company co-owner Akshay Mohan has said the school suspended operations the same day as the crash.

Witnesses saw the single-engine plane make several passes. During one of the "real low" passes, at about 200 to 250 feet, "the nose dropped and the tail went straight up," the report quoted witnesses as saying.

The plane spun into the ground even as the pilot apparently tried to recover by adding full power, the report said. After inspecting the wreckage, investigators found the throttle at the highest power setting, the report said.

The plane came to rest on its back, with the airframe smashed. Witnesses were able to extinguish an engine fire, the report said.

Rozelle held an airline transport pilot certificate as well as a flight instructor license.

The Federal Aviation Administration has launched an investigation into the company's operations and maintenance procedures.

Both telephone numbers listed on the Kemper Web site rang unanswered after hours Saturday and no one responded to an e-mail.