United Checking Its 757s, Causing Delays

United Airlines says it is "notifying customers traveling this evening or tomorrow on 757s that they may experience delays or cancellations due to unscheduled maintenance checks." United has 96 Boeing 757s.

At least 17 flights had been cancelled, and an unspecified number delayed, the Associated Press reports.

United says the 757 fleet is not "grounded" as "the planes will fly as the work is done." The necessary checks take approximately 60 to 90 minutes to complete and the airline began checking some of the aircraft late Tuesday. It expects that all of the checks will be completed by the end of Wednesday.

The checks, according to United, are necessary because during the last updating of the air data computers on United's 757s, a system that checks atmospheric conditions around the aircraft while in flight, "parts of the checks were not done as outlined by FAA directive". However, "all of the computer systems have been fully functional since they were installed."