Backdoor pilot

A television pilot (also known as a pilot or a pilot episode and sometimes marketed as a tele-movie) is a standalone episode of a television series that is used to sell the show to a television network. At the time of its creation, the pilot is meant to be the testing ground to gauge whether a series will be successful, and is therefore a test episode of an intended television series. It is an early step in the development of a television series, much like pilot studies serve as precursors to the start of larger activity. In the case of a successful television series, the pilot is commonly the very first episode that is aired of the particular series under its own name. A "back door pilot", is an episode of an existing successful series, that features future tie-in characters of an up-and-coming television series or film. The purpose of the "back door pilot" is to introduce the characters to an audience before the creators decide on whether they want to pursue a spin-off series with those characters or not.

Television networks use pilots to discover whether an entertaining concept can be successfully realized. After seeing this sample of the proposed product, networks will then determine whether the expense of additional episodes is justified. They are best thought of as prototypes of the show that is to follow, because elements often change from pilot to series. Variety estimates that only a little over a quarter of all pilots made for American television proceed to the series stage, although the figure may be even lower.

Most pilots are never publicly screened if they fail to sell a series. If a series eventuates, pilots are usually—but not always—broadcast as the introductory episode of the series.

Each summer (in the Northern hemisphere) or winter (in the Southern hemisphere), the major American broadcast television networks – including ABC, CBS, The CW, Fox and NBC – receive about 500 brief elevator pitches each for new shows from writers and producers. That fall, each network requests scripts for about 70 pitches and, the following January (which would be winter in the Northern hemisphere and summer in the Southern hemisphere), orders about 20 pilot episodes. Actors come to Los Angeles from within the area or elsewhere in the United States and around the world to audition for them. By spring (Northern hemisphere)/fall (Southern hemisphere), actors are cast and production crews assembled to produce the pilots.

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Wikipedia