The N.T.S.B. releases its preliminary report into a Florida plane crash last month that killed a UK professor and his pilot.
David Maehr's plane went down near the airport in Lake Placid.
The biology professor was surveying black bears in the area at the time.
He did similar work in eastern Kentucky.
The N.T.S.B. report indicates the plane had several significant modifications, and had just refueled 30 minutes before it went down.
Inspectors say it crashed in a near vertical, nose-down position with a lot of twisting and bending in the fuselage.