United grounds 757s to check air-data software

By Julie Johnsson
Posted Feb. 15 at 7:48 p.m.

United Airlines has grounded its fleet of 96 Boeing 757s after determining that the planes’ air data computer software did not comply with a Federal Aviation Administration airworthiness directive.

United began testing its 757s late Tuesday afternoon and may delay or cancel flights until the process is completed in 12 to 24 hours, said United spokeswoman Megan McCarthy. The software checks take approximately 60 to 90 minutes per plane.

“We apologize for any inconvenience and ask customers to check their flights status on United.com before going to the airport,” McCarthy said. As of 6 p.m. Central time, United had canceled only seven flights on its Tuesday schedule, according to FlightStats.com.

United is scrambling to comply with a 2004 FAA airworthiness directive that spelled out software and hardware changes for air-data computer systems in Boeing 757, 767 and 747 aircraft. “This action is necessary to ensure that the flight crew is able to silence an erroneous overspeed or stall aural warning,” the directive stated.

On a routine maintenance check Tuesday, United discovered that it hadn’t followed all of the steps mandated by the FAA to address safety concerns with the 757 flight computers that measure air speed and monitor atmospheric conditions.

United installed the software required by federal regulators in 2004 but hadn’t performed all of the necessary checks. The 757s’ air data computer systems have been “fully functional,” McCarthy said.

Chicago-based United acted voluntarily and not at the behest of federal regulators, said FAA spokeswoman Elizabeth Isham Cory.

The action does not affect Boeing 757 aircraft flown by Continental Airlines, which merged with United in October. The two continue to operate separately and won’t combine 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 issue that has made headlines in the last year.


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  1. RandyRandy Feb. 15 at 7:33 pm

    Julie: I’m not sure what ancient data your still clinging to, but UAL ceased being the “world’s largest carrier” back when the Delta/NWA deal was closed!

  2. juliejohnsson Feb. 15 at 7:38 pm

    Sorry dear reader, but Delta lost that crown when the the United-Continental merger closed Oct. 1.

  3. noitall Feb. 15 at 7:51 pm

    Sorry dear Julie, but UA and CO are separate carriers which happend to be owned by the same holding company. For the time being DL’s single operating certificate makes it the largest carrier.

  4. Jed Feb. 15 at 8:54 pm

    hehehe…Mine is bigger than yours.

  5. skeptic Feb. 15 at 9:44 pm

    Why did WGN-TV this evening show a 747 when they were discussing 757s? Do reporters not engage in the basic of journalistic research?

  6. Arrelious Feb. 15 at 9:58 pm
  7. phydeaux3 Feb. 16 at 5:18 a.m.

    “United installed the software required by federal regulators in 2004 but hadn’t performed all of the necessary checks”

    Sounds like their technical support and engineering staff has a problem reading and/or following instructions.

    When an AWD is issued, the staff of the airline is to issue a set of maintenance instructions and workcards in order that the inspection or action to be taken is fully integrated in the maintenance routine and record keeping system of the respective organization.

    Scheduling is the next step. Sounds like they wanted to get it out of the way too fast (accomplish on a routine overnight maintenance schedule) or delegated this work to a third party maintenance station.

    Installing software into the avionics system is not too terribly difficult, just time consuming. In many cases, this software is still on floppy disks so there are normally quite a number of disks to install in a sequential manner and, of course, someone to monitor the progress while trying to stay awake.

    Testing the system comprises of attaching special equipment to the external pitot tubes and sensors on the airplane. It can take time to simulate a flight condition with the test set, and this sounds like the point where they just conveniently sidestepped the proper procedure and signed off the software installation as good and in compliance with the FAA order.