"Nightmare at 20,000 Feet" is episode 123 of the American television anthology series The Twilight Zone, based on the short story of the same name by Richard Matheson, first published in Alone by Night (1961). It originally aired on October 11, 1963.

While traveling by airliner, Bob Wilson thinks he sees a gremlin on the wing. Bob tries to alert his wife and the flight crew to the gremlin's presence, but every time someone else looks out of the window, the gremlin leaps out of view, so Bob's claim seems outlandish. His credibility is further marred because this is his first flight since his nervous breakdown six months earlier, which also occurred on an aircraft. Bob realizes that his wife is starting to think he needs to go back to the sanitarium, but his bigger concern is that, if nothing is done about the gremlin, it will damage the airliner and cause it to crash. He sees the gremlin tinker with the wiring under one of the engine cowlings.

After repeated attempts to warn the crew, Bob grows desperate, steals a sleeping police officer's revolver, and opens the window marked "Auxiliary Exit" to shoot the gremlin, succeeding despite being nearly blown out of the aircraft himself. Once the airliner has landed, everyone believes that he has gone insane. As Bob is whisked away in a straitjacket, he tells his wife that he is alone in his knowledge of what happened during the flight. Rod Serling informs the viewers that the truth will soon be more widely known and the final shot reveals why: damage to the aircraft's wing, caused by the gremlin.

The episode was remade in 1983 by director George Miller as a segment of Twilight Zone: The Movie. Unlike Bob Wilson, whose credibility was compromised by a recent nervous breakdown in the 1963 version, John Valentine, played by John Lithgow, suffers from severe aviatophobia, again giving the flight crew added reason to disbelieve his wild claims.

...
Wikipedia