'Widespread cracking' found where hole opened on Southwest jet

A flight attendant received minor injuries when the hole opened and the cabin depressurized 18 minutes after the plane took off from Phoenix bound for Sacramento, California, NTSB member Robert Sumwalt told reporters.

The flight data recorder indicated the plane was cruising at 36,000 feet when it depressurized, but it dropped to 11,000 within 4 1/2 minutes, Sumwalt said.

The pilot initially planned to return to Phoenix to land, but after the flight attendants reported seeing blue sky through the jet's roof he made an emergency landing at a military base in Yuma, Arizona, Sumwalt said.

The initial inspection found "clear evidence that the skin separated at the lower rivet line" where "the skin comes together on the aircraft," Sumwalt said.

The cracking would likely not be visible during routine inspections, but could have been seen when the plane underwent major maintenance and was disassembled in March 2010, Sumwalt said.

The hole that opened up was 5 feet long and 1 foot wide, he said.

Southwest mechanics cut away the section of the plane containing the hole and are sending it overnight to the NTSB laboratory in Washington, the board said.

Southwest grounded 79 of its planes for inspection for "aircraft skin fatigue" Saturday.

As of Sunday afternoon, 19 planes were returned to service after "intense inspection," the airline said in a statement. However, "small, subsurface cracks" or indications of cracks were detected in three other aircraft.

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