The airline conducted the inspections after a hole tore open the roof of one of its 737s on Friday on flight from Phoenix to Sacramento, forcing the airplane to make an emergency landing at a military base.
Friday‘s incident has prompted the Federal Aviation Administration to say that it would issue a directive requiring all airlines to inspect some older-model Boeing 737s for cracks in the skin that can be caused by pressurization and depressurization of the cabin over thousands of takeoffs and landings. Boeing, the manufacturer, said it was also recommending that airlines inspect the areas where the skin covers joints on the older 737 models.
Southwest canceled about 670 flights over the weekend and on Monday while it inspected nearly 80 aircraft. On Tuesday, a Southwest spokeswoman, Whitney Eichinger, said the airline had resumed full scheduling of its 3,400 daily flights, despite the absence of the five planes taken out of service.
“We are waiting for further instructions from Boeing on how to complete the repairs,” Ms. Eichinger said.
Friday’s crack was at least the third involving metal fatigue in the last few years, and the most terrifying. The others involved another Southwest 737-300 flight in 2009 and an American Airlines Boeing 757 last year.
The recent string of similar problems has baffled safety experts who said the industry assumed it had successfully resolved the problem of metal fatigue after an accident in 1988 involving a 737 jet flown by Aloha Airlines. During the flight, an 18-foot section of the forward cabin ripped open and a flight attendant was blown out of the plane.
The F.A.A. announcement applies to 175 aircraft worldwide, including 80 that are based in the United States, most of them operated by Southwest.
Southwest insisted that it had done all the required inspections of its aircraft. But the latest problem focused attention on how the carrier uses its planes on up to 12 flight segments a day. Other airlines, which often fly longer routes, typically have six to eight segments for their planes. The plane involved in the incident on Friday had logged 39,000 takeoffs and landings, a relatively high number for a 15-year-old aircraft.
Asked whether there were any changes to the number of segments, Ms. Eichinger said deferred to the National Transportation Safety Board investigation.
The F.A.A. directive focused on planes that had accumulated a large number of takeoff and landing cycles. It applies not only to the 737-300 model but also to similar 737-400 and 500 models, a design that dates back to the early 1980s and is known as the 737 Classic series.
“This was a very serious failure,” said William R. Voss, the president and chief executive of the Flight Safety Foundation, an independent nonprofit group. “Is there something wrong with the inspections we’ve been using in the past 20 years, or was there something wrong on the inspection with this one plane?”
Hans J. Weber, owner of Tecop International, an aviation consulting firm in San Diego, said that jetliners could easily survive a small crack in the aluminum skin on the fuselage. But what happened in the Aloha accident and the more recent incidents is that multiple small cracks appeared near rivets in areas where the plane experiences the most stress, causing the skin to peel back. “It’s like it unzips,” Mr. Weber said.
The F.A.A. directive is intended to detect cracks in places where the skins overlap and other structural weaknesses, J. Randolph Babbitt, the F.A.A. administrator, said in a statement.
The N.T.S.B. said that it was probably the result of fatigue cracks in these joints. Southwest began flying the plane, which carried 118 passengers, in 1996 and it is among the oldest in its fleet.
Mr. Weber said that after the Aloha accident, metal fatigue was a big issue, and the F.A.A. began to require the airlines to conduct more frequent and intense inspections as planes aged and accumulated more takeoffs and landings.
“Over the last few years, the attitude has been that we solved the fatigue problem,” he said. “But are we seeing what happens when attention wanders to something else, that we slip a little bit in the quality of the work we do? This is just speculation, but this is what I’m worried about.”
Article source: http://feeds.nytimes.com/click.phdo?i=b6a432545c1e356dd06cebd72f4c1560