The N.T.S.B.’s report indicated that Dennis Dutton and his adult son Jack were at the controls of the Cessna C550, which was registered to Mr. Biffle. Mr. Dutton, whom the report refers to as “the pilot,” served in the Air Force and spent over three decades flying for Delta Air Lines, according to his obituary. But his credentials required him to have a second in command when operating Mr. Biffle’s type of Cessna, the report said, and Jack Dutton — whom the report refers to as “the pilot’s adult son” — was not qualified to serve as a second in command, investigators said.