Southwest Airlines Co. said it will scrub 100 more flights today and reported “small, subsurface cracks” in two jets during inspections for metal fatigue after a plane’s fuselage tore open in flight.
The dropped flights follow 300 cancellations yesterday, or 9 percent of the schedule, said Chris Mainz, a spokesman. Checks on 21 Boeing Co. 737-300 planes found two that needed repair, and 19 others were returned to service, Southwest said. The Associated Press reported cracks were found in three jets.
The April 1 incident on Flight 812 spurred checks of 79 of Dallas-based Southwest’s 737-300s. Airlines must make regular checks of their planes for metal fatigue, which can occur as jets endure the stress of takeoffs, landings and low outside air pressure of high-altitude flight.
“Assuming proper inspections were carried out at the proper intervals, the issue appears to be whether or not the intervals were adequate to catch the rapid propagation of what are reported as ‘multisite’ fatigue cracks,” said Bob Mann, president of consultant R.W. Mann & Co.
Investigators probably also will look at whether the repetitive inspection process “actually contributes to accelerating the propagation of cracks,” said Mann, who is based in Port Washington, New York.
The National Transportation Safety Board said yesterday that the jet showed signs of fatigue cracking near the hole in the hull after it was inspected following an emergency landing in Yuma, Arizona. Flight 812 passengers described the hole as being 1 foot (0.3 meters) wide by 3 feet long, said Linda Rutherford, an airline spokeswoman.
Another spokeswoman, Whitney Eichinger, said today’s cancellations would be fewer than the approximately 300 flights scrubbed on each of the past two days because the airline was getting more of the 737-300s back in service.
Southwest is the world’s biggest operator of 737s, the world’s most widely flown airliner. Its 548-plane fleet consists solely of different models of the 737.
Metal fatigue was blamed for an 18-by-12 inch rip in a Southwest 737 in July that was flying at 35,000 feet, an incident that also forced an emergency landing. In January 2010, the Federal Aviation Administration ordered fuselage checks for metal fatigue on 135 737-300s, -400s and -500s in the U.S., after Boeing recommended such checks in September 2009.
A Boeing spokesman, Marc Birtel, said no fleetwide action is being taken for the line of 737s. The Chicago-based planemaker is working with Southwest and the NTSB in the investigation, and will take action if there’s a need, he said.
The April 1 incident occurred as Flight 812 was bound for Sacramento, California, from Phoenix. A flight attendant and a passenger were injured, said Rutherford, the airline spokeswoman.
The plane will be 15 years old in June; its fuselage skin had been inspected on March 29 and Feb. 5, Rutherford said.
According to the airline’s website, it had 171 737-300s as of Dec. 31, 2010. The average age of those aircraft was 19 years as of the end of 2010.
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