Authorities struggled to explain how a small plane crashed at an international airport, erupted in fire, but evidently went unnoticed for hours.
The incident occurred early Tuesday in Nashville.
But exactly what time remains a mystery.
The single-engine Cessna registered to the Windsor Flying Club in Ontario, Canada, evidently crashed sometime after 3 a.m. local time, according to the National Transportation Safety Board.
But it wasn't noticed until well after sunrise when another plane taxiing for take-off saw an engine cover on the edge of runway 2C -- the middle of three parallel runways.
Controllers contacted airport personnel, who found the fire-scarred wreckage. The plane's sole occupant was dead, officials said.
The airport's control tower is staffed 24 hours a day, the Federal Aviation Administration told CNN. But it was not immediately clear how many controllers were in the tower during the overnight shift.
An FAA spokesman said there was low visibility overnight and fog.
Another FAA spokesman said it was not known whether the plane had been in contact with controllers, or if it had made a distress call.
The agency declined to answer questions, saying the matter was under investigation.
Airport spokeswoman Shannon Sumrall referred all questions to the NTSB.
The board spokesman, Peter Knudson, said the aircraft suffered a post-crash fire and the cause of the crash is under investigation.
The name of the victim was not released.