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United Airlines Grounds 757s At SFO, Nationwide

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A United Airlines 757 in flight after takeoff from San Francisco International Airport. (AP file photo)

A United Airlines 757 in flight after takeoff from San Francisco International Airport. (AP file photo)

SAN FRANCISCO (CBS 5 / AP) — United Airlines on Tuesday temporarily grounded 96 aircraft, all of them Boeing 757s, while the carrier performs maintenance checks that were not completed.

San Francisco International Airport serves as a major hub for United, and the airline told CBS 5 that numerous 757s fly out of SFO daily — most notably to New York’s JFK airport.

Nationwide, the grounding caused at least 25 flights to be canceled and an unspecified number of delays. The maintenance checks can take anywhere from 60 to 90 minutes.

The issue could affect United’s schedule into Wednesday, the airline warned.

Airline spokeswoman Megan McCarthy said United grounded the Boeing 757 aircraft because the carrier determined that it had not completed operational checks after updating air data computers following a 2004 federal directive. She noted that all of the computers are fully functional.

McCarthy said the airline discovered the oversight earlier Tuesday during routine quality assurance checks.

The Federal Aviation Administration indicated that United’s move was purely voluntary.

United and Continental combined last year to create the world’s largest airline, but currently operate separately under parent holding company United Continental Holdings Inc.

The grounding impacted only affected United’s fleet of Boeing 757s. McCarthy said Continental’s fleet of 62 757s weren’t grounded.

The federal airworthiness directive, cited by United, requires a modification of the air data computer system on certain Boeing aircraft.

It involves installing new circuit breakers, relays, and related components, and making various wiring changes in and between the flight deck and main equipment center.

According to the published directive, the actions were necessary to ensure that the flight crew is able to silence an erroneous overspeed or stall warning. A persistent erroneous warning could confuse and distract the flight crew and lead to an increase in the flight crew’s workload. Such a situation could lead the flight crew to act on hazardously misleading information, which could result in loss of control of the airplane, according to the directive.

The directive was effective June 22, 2004.

(Copyright 2011 by CBS Broadcasting Inc. and The Associated Press. All Rights Reserved.)

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