A scope clause, at least as used in a pilot contract, basically states that an airline cannot use pilots other than its own to fly its flights. The largest application of the scope clause has been to limit the use of regional jets. Such a scope clause might say, for example, that all aircraft with more than 50 seats must be flown by pilots of the major airline. Such a scope clause would limit a carriers regional feeders to flying aircraft of 50 seats or fewer. The scope clause was also cited by American's pilots after the Reno Air acquisition... the APA insisted that, by allowing Reno's pilots to continue flying under Reno's contract after the purchase was completed was a violation of the scope clause. I believe that the term comes from the fact that this clause defines the scope of the contract; that is, it tells who is and who is not covered by the contract.