US safety inspectors said they found pre-existing damage in the form of 'widespread cracking' on a passenger jet that made an emergency landing after a hole ripped open on the fuselage.
Southwest Airlines canceled another 300 flights to accommodate inspection of 79 Boeing 737-300 planes in the company's fleet, specifically to address possible "skin fatigue" on ageing airliners.
None of the 123 people on Flight 812 was seriously hurt when the hole tore open with a loud bang en route from Phoenix, Arizona, to Sacramento, California, on Friday, causing a sudden loss of pressure and triggering a harrowing journey that saw passengers grasp for oxygen masks and frantically text loved ones.
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The plane, suffering from a five-foot by one-foot (1.5-meter by 0.3-meter) gash in its roof, landed without incident at an Arizona military base, where the National Transportation Safety Board (NTSB) is examining the damaged jet.
"We did find evidence of widespread cracking across this entire fracture surface," NTSB member Robert Sumwalt told a press briefing broadcast from Yuma via Internet.
"There was pre-existing fatigue along the entire fracture surface," added Sumwalt, who described how two panels of the aircraft's aluminum alloy skin separated at a rivet line.
Investigators will cut out the damaged area and ship it to Washington for a more thorough examination, Sumwalt said.
When asked about reports that cracks on the plane's frame were found and repaired a year ago, Sumwalt said the NTSB had yet to review the maintenance records, but said any such damage likely would have been detected during the jet's last heavy maintenance check, which was conducted last March.
"Was the aircraft well maintained and should it have been maintained better? That is exactly why we are here, to look at why this problem occurred," he said.
Southwest said the plane had undergone all necessary Federal Aviation Administration inspections, including the extensive overhaul in March 2010, and was given a routine inspection on Tuesday, according to Fox News.
Southwest's entire fleet of 548 planes is comprised of 737s, including about 170 Boeing 737-300s, the oldest in the fleet.
The airline's planes average 11.2 years of age. Boeing 737-300s were produced from 1984 to 1999.
Spokeswoman Linda Rutherford said Southwest had replaced the skin on several of its 737-300s, but that the planes grounded Saturday had not had such work done, Fox reported.
"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," Rutherford said.
