- Associated Press - Monday, April 4, 2011

YUMA, Ariz. (AP) — Three more Southwest Airlines jetliners have small, subsurface cracks that are similar to the cracks suspected of playing a role in the fuselage tear of a Boeing 737-300, causing the aircraft to lose pressure and forcing a frightening emergency landing, officials said.

The 5-foot-long hole tore open in the passenger cabin roof shortly after the plane left Phoenix for Sacramento, Calif., Friday afternoon. None of the 118 people aboard was seriously hurt as the plane descended from 34,400 feet to a military base in Yuma, 150 miles southwest of Phoenix.

Since then, Southwest grounded its 79 other Boeing 737-300s and began inspecting them.

Sunday night, another SouthwestBoeing jet was diverted, this time because of a burning electrical smell in the passenger cabin, Southwest and Los Angeles International Airport officials said.

The plane carrying 142 people was en route from Oakland, Calif., to San Diego when it made an unscheduled landing about 8 p.m. PDT in Los Angeles, where passengers changed planes and continued on their journey, Southwest spokeswoman Whitney Eichinger said. No one was hurt.

A member of the National Transportation Safety Board investigating the emergency landing of Southwest Airlines Flight 812 cuts away a portion of the plane's fuselage on Sunday in Yuma, Ariz. (AP Photo)
A member of the National Transportation Safety Board investigating the emergency landing ... more >

She said the cause of electrical smell is being investigated, but it “was completely unrelated to the issue in Arizona.”

Like the Arizona plane, Sunday’s aircraft was also a Boeing 737-300. But Ms. Eichinger said it wasn’t among the 79 planes Boeing grounded for inspections. She said the inspections weren’t required for the aircraft because it was manufactured differently, but she didn’t elaborate.

In its statement on the inspections, Southwest said Sunday that two planes have been found to have cracks similar to those in the stricken aircraft and will be evaluated and repaired before they are returned to service. A National Transportation Safety Board member told the Associated Press later that a third plane had been found with cracks developing.

The other 19 aircraft inspected so far showed no problems and will be returned to service.

Checks on the remaining jets are expected to be completed by late Tuesday, the airline said. That means flight cancelations likely will continue until the planes are back in the air. About 600 flights in all were canceled over the weekend after Southwest grounded the planes.

The cracks found in the three planes developed in two lines of riveted joints that run the length of the aircraft. The agency is focusing its probe on the area of the cracks but has not determined that the cracks caused the rupture.

NTSB member Robert Sumwalt said Boeing was developing a “service bulletin” for all 737-300 models with comparable flight-cycle time as the Arizona jet, which was 15 years old and had about 39,000 takeoff-and-landing cycles.

There are 931 such models in service worldwide, 288 of which in the U.S. fleet.

Boeing’s bulletin would strongly suggest extensive checks of two lines of “lap joints” that run the length of the fuselage. The NTSB has not mandated the checks, but Mr. Sumwalt said the FAA is likely to make them mandatory.

The tear along a riveted “lap joint” near the roof of the stricken plane above the midsection shows evidence of extensive cracking that hadn’t been discovered during routine maintenance before the flight — and probably wouldn’t have been unless mechanics specifically looked for it, officials said.

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