More Southwest Airlines flights canceled

Southwest Airlines is expecting to cancel about 100 flights nationwide Monday as it continues to inspect its air fleet over safety concerns, company officials said.

On Friday, Flight 812 was about 18 minutes into its flight out of Phoenix when a 5-by-1-foot 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.

Southwest canceled about 600 flights over the weekend to conduct inspections. It found three other planes with small cracks that were being evaluated, the safety board said.

Investigators revealed 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.