United Airlines operations are returning to normal after the carrier voluntarily grounded its fleet of 96 Boeing 757s Tuesday to ensure the planes’ air-data computer software complied with a Federal Aviation Administration airworthiness directive.
The Chicago-based carrier was able to quickly carry out the software checks needed to meet federal guidelines, and most of the aircraft were back in service by mid-day Wednesday.
United expects to operate a normal schedule Wednesday after canceling 15 flights Tuesday as it scrambled to perform software checks that took 60 to 90 minutes per 757, said Megan McCarthy, spokeswoman for the carrier.
Airlines face fines and direct government intervention if they don’t follow the federal government’s safety directives down to the letter. The FAA last year slapped American Airlines with a $24.2 million civil penalty, the largest it had ever levied, for failing to properly bundle wires in the wheel wells of its workhorse MD-80 aircraft fleet.
United discovered in an internal quality assurance audit Tuesday that it hadn’t correctly followed a 2004 FAA airworthiness directive that spelled out software and hardware changes for air data computer systems in Boeing 757, 767 and 747 aircraft. While United had installed the software required by federal regulators, it hadn’t performed all of the necessary operations checks for its Boeing 757s. Even so, the planes’ air data computer systems have been “fully functional,” McCarthy said.
Those systems monitor atmospheric conditions through a variety of probes to help flight computers determine what an aircraft’s maximum and minimum speeds should be and to sound speed sensitive warnings.
“This action is necessary to ensure that the flight crew is able to silence an erroneous overspeed or stall aural warning,” the directive stated.
The action does not affect Boeing 757 aircraft flown by Continental Airlines, which merged with United in October to form the world’s largest airline. The carriers have combined financial results but won’t meld fleets, flight crews and maintenance stations until they gain a single operating certificate from the FAA.
United’s action is not related to electrical shorts that have caused some 757 windshields to crack, said FAA spokeswoman Laura Brown, referring to another safety issue that has made headlines over the last year.