United grounds its entire 757 fleet

Airline conducts round of air data computer system checks

Many United flights remain cancelled or heavily delayed today as United Airlines performs technical maintenance checks on its Boeing 757 fleet.
“Specifically … United is performing follow-up maintenance checks … to the air data computers on its 96 Boeing 757s,” said airline spokesperson Rahsaan Johnson.
“All of the air data computers are fully functional. The checks are necessary as part of a modification process to the system.”
Once the checks are complete, the airline should return to normal service later today. The procedures last between 60 and 90 minutes per aircraft.
The checks are said to be in compliance with a 2004 Federal Aviation Administration airworthiness directive requiring a modification to the air data computer system. This is supposed to ensure that crews are able to stop an erroneous over-speed or stall warning.