SEATTLE - Alaska Airlines had completed 16 of an expected 17 inspections of MD-80 aircraft by midday Friday, one day after announcing that a tool used to measure stresses on the jets' tail sections may have given the wrong readings.
Alaska said the tool in question, made by the airline itself, could give incorrect measurements of stresses on jackscrews in the MD-80s' horizontal stabilizers. The same part has been implicated in the Jan. 31 crash of Alaska Flight 261 off the California coast that killed all 88 people aboard.
The National Transportation Safety Board, which is investigating that accident, confirmed Friday that it will look into Alaska's use of its measurement tool as an alternative to one made by the MD-80's manufacturer, McDonnell Douglas, now part of The Boeing Co. The jackscrew on Flight 261 was found to have been stripped.
Alaska spokesman Jack Evans said Friday stress measurements on the 16 aircraft inspected were correct and did not show any additional wear and tear. Those planes were back in service, and the company expected to inspect the final MD-80s by day's end.
Originally, the company said 18 jets would be grounded for the inspections, but Evans said one of those was found to have been tested with the McDonnell Douglas tool and not in need of an additional check.
Airline officials told the Federal Aviation Administration on Thursday that its tool used to check jackscrews may have produced incorrect readings. The jackscrew assembly consists of a nut that rides up and down a screw as it is turned to raise and lower the stabilizer, a winglike part of the tail that is used to raise or lower the nose of a plane in flight.
There were no indications of problems, but other airlines also have been told to check MD-80 and DC-9 planes, according to an FAA statement.
The scramble resulted in cancellation of 18 Alaska Airlines flights late Thursday, including eight from the company's principal hub at Seattle-Tacoma International Airport. An additional 29 flights were canceled Friday, Evans said, far below the 72 flights the company had estimated.
''We're having a better day than we thought we would,'' Evans said. ''Even for a Friday before a busy summer weekend, this is pretty good.''
Alaska Airlines, the dominant carrier on north-south routes along the West Coast, normally operates about 500 flights a day with a fleet of 90 planes, including 34 MD-80s.
Boeing took over production of the MD-80, which is based on the DC-9 airframe, after absorbing McDonnell Douglas in a $16.3 billion merger in 1997. Out of about 2,000 MD-80-series and DC-9 jetliners worldwide, more than 1,100 are flown by U.S. carriers.
After the Alaska Flight 261 crash, the FAA inspected the airline's maintenance facilities and found more than 150 instances of improper or missing paperwork. The probe found that maintenance had been done correctly, however.
A criminal investigation into the crash has focused on a mechanic's decision not to replace a jackscrew assembly. The jackscrew had been tested repeatedly and found to be nearly worn out but was returned to service after a second crew retested it a few days later. Two Alaska Airlines mechanics from that second crew insisted in an interview with The Seattle Times that they were not at fault.
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