If you were scheduled on a United 757 earlier today and are wondering why it was canceled, we now know why. According to the Wall St. Journal, the airline is in the process of grounding its entire fleet in order to perform maintenance checks to air data computers that were modified earlier this year.
According to Gadling’s resident pilot Kent Wien:
There are two air data computers on every 757 and they’re used to take inputs from pitot tubes, static ports and temperature probes to determine the speed, rate of climb and altitude of the airplane. Any difference in the captain and the co-pilot’s side requires a quick determination as to which side is giving the correct data. In 1996 a 757 experienced a blocked pitot tube that caused it to crash off the coast of the Dominican Republic. While not the same problem as an ADC failure, the failures would look very similar to the pilots.
In this specific case, checks have acturally already been completed on the 96 767s; this round of study is in order to comply with Federal Aviation Administration requirements that were not followed at that time. Continental‘s 62 aircraft are not affected.
Each check takes less than two hours so the groundings should be brief. But operation on the aircraft will be disrupted for the rest of today and into tomorrow’s schedules.
Contacted for comment, United Airlines’ Charles Hobart confirmed:
We have about 25 cancellations. The maintenance checks are ongoing and will continue until completed. We expect minimal further disruption tomorrow.