- Associated Press - Sunday, April 3, 2011

YUMA, Ariz. (AP) — Federal records show that cracks were found and repaired a year ago in the frame of the Southwest Airlines Boeing 737-300 that made an emergency landing at an Arizona military base after a hole was torn from the passenger cabin.

No one was seriously injured Friday as the aircraft carrying 118 people rapidly lost cabin pressure and made a harrowing but controlled descent from 34,500 feet, landing safely near Yuma, Ariz., 150 miles southwest of Phoenix.

But passengers recalled tense minutes after a hole ruptured overhead with a blast and they fumbled frantically for oxygen masks as the plane descended.

On Sunday, federal investigators examining the damaged plane in Yuma said the entire length of a 5-foot-long tear in the skin of the aircraft shows evidence of pre-existing fatigue cracking.

National Transportation Safety Board member Robert Sumwalt said that the rip was a foot wide and that it started along a lap joint where two sections of the 737’s skin are riveted together. Southwest mechanics will cut the entire ripped section out of the plane, and it will be sent to Washington for analysis.

Southwest grounded 80 similar planes to carry out inspections.

An Associated Press review of Federal Aviation Administration records of maintenance problems for the 15-year-old plane showed that in March 2010 at least eight instances were found of cracking in the aircraft frame, which is part of the fuselage, and another half-dozen instances of cracked stringer clips, which help hold the plane’s skin on. The records showed that those problems were repaired.

It’s not uncommon for fuselage cracks to be found during inspections of planes that age, especially during scheduled heavy maintenance checks, in which they are taken apart so that inspectors can see into areas not normally visible.

The National Transportation Safety Board was working to determine what caused part of the fuselage to rupture.

NTSB member Robert Sumwalt said investigators will study the cut-out fuselage piece for fracture patterns and examine the plane’s black box and flight recorders.

Southwest officials said the Arizona plane had undergone all inspections required by the FAA. They said the plane was given a routine inspection Tuesday and underwent its last so-called heavy check, a more costly and extensive overhaul, in March 2010.

Meanwhile, the airline grounded the 80 planes resulting in about 300 canceled flights Saturday, airline spokeswoman Linda Rutherford said.

Southwest operates about 170 of the 737-300s in its fleet of about 540 planes, but it replaced the aluminum skin on many of the 300s in recent years, Ms. Rutherford said. The planes that were grounded Saturday have not had their skin replaced, she said.

“Obviously we’re dealing with a skin issue, and we believe that these 80 airplanes are covered by a set of (federal safety rules) that make them candidates to do this additional inspection that Boeing is devising for us,” Ms. Rutherford said.

Julie O’Donnell, an aviation safety spokeswoman for Seattle-based Boeing Commercial Airplanes, confirmed “a hole in the fuselage and a depressurization event” in the latest incident but declined to speculate on what caused it.

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