Impact of Alaska Airlines jet grounding lighter than expected

An Alaska Airlines MD-80 is shown in this file photo.

OAKLAND, California (CNN) -- Alaska Airlines on Friday revised downward, from 50 to 30, the number of flight cancellations expected this weekend from its grounding of 18 MD-80 jets.

The airline grounded the MD-80s late Thursday to recheck a part of their tail assemblies, the same part suspected in January's deadly Alaska Airlines MD-80 crash near Los Angeles that killed all 88 people aboard.

Mechanics worked through Thursday night to check the aircraft, after the airline said it learned that some of the tools used the check the part -- known as a jackscrew -- may have given inaccurate readings. Inspections take two to four hours for each plane, the airline said.

AUDIO Bill Ayer, president and chief operaating officer of Alaska Airlines, talks about the tools used when inspecting MD-80 jackscrews 291K/27 sec. AIFF or WAV sound     RESOURCES Zoom in: How the MD-83 stabilizer works Timeline of recent crashes Image gallery: The crash of Flight 261 Facts about Alaska Airlines     MESSAGE BOARD Air Safety

Most of the airline's MD-80s pulled for inspection were to be checked at facilities in Seattle, where most of the planes were expected to be routed, the airline said. Other inspections were expected to take place in Oakland, California, Phoenix and San Francisco. The airline has 34 MD-80 jets.

Bill Ayer, the airline's president and chief operating officer, said his company was working hard to "minimize the cancellations."

Federal investigators have not yet determined the cause of the crash in January, but have focused on the jackscrew and its accompanying gimble nut assembly that apparently failed, leading to the crash.

The jackscrew helps control the aircraft's horizontal stabilizer, which helps to move the plane upward and downward.

Paul Turk, a spokesman for the FAA, said all airlines with MD-80s in their fleets will be asked to check the tools used to check the jackscrews in light of Alaska Airlines' decision. Turk said DC-9 planes are also affected.

This part, known as a jackscrew, is being rechecked on 18 Alaska Airlines MD-80 jets

The problem came to light when Alaska Airlines tested its jackscrews, and found that the tools used to measure their tolerance may not have given accurate readings. Machines made by Boeing to test jackscrews are not in question. However, so-called "second tier" tools, which are copies of the Boeing-made machines, have been found to give faulty readings in some circumstances.

When Alaska Airlines tested its jackscrews in the aftermath of the crash, the parts were found to be within accepted tolerance levels. It is not known whether a Boeing machine or a "second tier" machine was used to perform those tests.

The FAA statement said the National Transportation Safety Board is assisting with the checks.

The grounding of the Alaska Airlines planes, as well as the alert issued to all airlines, could greatly affect air traffic and travel in the United States.

Turk said international carriers were also notified of the problem.

Ayer referred passengers to the airline's website -- http://www.alaskaair.com -- for information about flight cancellations.

CNN San Francisco Bureau Chief Greg Lefevre contributed to this report.

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Alaska Airlines
National Transportation Safety Board
Federal Aviation Administration

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