Which episode features William Shatner battling a gremlin on an airplane wing?

The Twilight Zone episode featuring William Shatner battling a gremlin on an airplane wing is Nightmare at 20,000 Feet. Shatner plays Robert Wilson, a passenger who sees a creature outside the aircraft window and watches it tamper with the plane during a stormy flight.

The episode was written by Richard Matheson and directed by Richard Donner. It originally aired on October 11, 1963, as the fifth episode of the show's fifth season. Its tension comes partly from Wilson's recent nervous breakdown: because he is the only person who can see the gremlin, the other passengers and crew suspect that he is hallucinating.

The story is based on Matheson's short story of the same name, first published in 1961. Its famous image became a lasting symbol of fear of flying and has been repeatedly parodied. The episode was also remade in 1983 as a segment of Twilight Zone: The Movie, with John Lithgow playing a different passenger named John Valentine. That remake is often confused with Shatner's original television performance.