Sully's got nothing on this guy ... a passenger in a small plane took the controls midair after the pilot became incapacitated ... and by a miracle he was able to land the aircraft safely.

It went down Tuesday at the Palm Beach International Airport. 

WPBF-TV in Palm Beach obtained video of the emergency after air traffic control received an alarming radio call ... not from the pilot, but from the passenger ... "I've got a serious situation here. My pilot has gone incoherent. I have no idea how to fly the airplane."

A serious situation is a gross understatement ... but the dude stayed calm as the tower operator jumped to the ready -- "Roger. What's your position?" The passenger responded with this chilling message ... "I can see the coast of Florida in front of me. And I have no idea."

The tower operator said, "Maintain wings level and just try to follow the coast, either north or southbound. We're trying to locate you."

Locate him they did -- 25 miles from the airport. Somehow the tower operator gently gave instructions to the passenger and the plane not only landed safely, but it was also a respectable landing even for a licensed pilot.

The FAA has not released the names of the passenger or pilot, and it did not reveal the nature of the medical emergency or the pilot's condition.