April 4, 2011 in Nation/World

Fatigue cracks discovered in Southwest plane fuselage

Checks find problem on two more airliners
Carla Rivera Los Angeles Times
 

LOS ANGELES – The National Transportation Safety Board will consider whether to upgrade inspection criteria on Southwest Airlines Boeing 737-300s and other aircraft after finding evidence of fatigue fractures in the torn section of a Sacramento, Calif.-bound plane that depressurized and made an emergency landing, authorities said Sunday.

Flight 812 was about 18 minutes into its flight out of Phoenix on Friday when a small section of the fuselage skin burst open, terrifying the 118 passengers, who had to scramble for oxygen masks after the cabin lost pressure. The plane landed safely at a military base in Yuma, Ariz.

After canceling 300 flights Saturday, Southwest canceled about 300 more flights Sunday because of inspections and found two other planes with small cracks, the airline said. Those cracks were being evaluated.

Investigators revealed earlier Sunday that tiny cracks had been found on the Flight 812 aircraft, around rivet holes along a joint where two areas of the fuselage skin overlap. They were trying to determine how long the cracks had been there. An inspection found “persistent fatigue along the entire fracture surface,” said safety board member Robert Sumwalt.

The cracks would not be immediately apparent from a visual inspection, a fact that prompted air safety officials to question whether new inspection criteria may be needed for the 737s and other aircraft.

There are “no existing criteria to perform inspections for this type of failure,” said Sumwalt, who was in Yuma with a team that included investigators from the NTSB, Federal Aviation Administration and the Boeing Co.

Southwest said it had begun a new round of testing to detect subsurface fatigue that would not be readily visible on the 79 planes the company pulled from service.

Nineteen planes had passed the intense inspection by Sunday afternoon and were returned to service.

“Our highest priority is the safety of our employees and customers,” Mike Van de Ven, Southwest’s chief operating officer, said in a statement.

“Prior to the event regarding Flight 812, we were in compliance with the FAA-mandated and Boeing-recommended structural inspection requirements for that aircraft. What we saw with Flight 812 was a new and unknown issue. … Delays and cancellations are never the preference, however we are taking every precaution we can to ensure that our operation is safe.”


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