NTSB: Cracks found in 3 grounded Southwest planes

By Nick Oza, The Arizona Republic via AP

Officials discovered cracks in more Southwest jeltiners, and the airline company grounded flights Monday for inspections.

EnlargeCloseBy Nick Oza, The Arizona Republic via AP

Officials discovered cracks in more Southwest jeltiners, and the airline company grounded flights Monday for inspections.

Boeing said Monday that it will issue guidance this week on how airlines should do checks on the affected airplanes now in service.

The 5-foot-long hole tore open Friday in the passenger cabin roof shortly after the Southwest plane carrying 118 people left Phoenix for Sacramento It made a rapid descent, landing at a military base in Yuma, 150 miles southwest of Phoenix. No one was seriously hurt.

Since then, Southwest grounded 79 other Boeing 737-300s and began inspecting them. The grounding caused about 600 flight cancellations over the weekend and another 70 on Monday. Nineteen inspected aircraft 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.

READ MORE: Cracks found in Southwest aircraftThe incident raises new questions about the vulnerability of the nation's air fleet to fatigue cracks, more than two decades after cracks caused part of the roof of an Aloha Airlines Boeing 737 to peel open. A flight attendant was sucked out and plunged to her death.

There are 931 737-300 such models in service worldwide, 288 of which are in the U.S. fleet. Boeing said its service bulletin will also require checks on some 737-400 and 737-500 models as well, depending on how many pressurization cycles they have gone through.

The new inspection would be a one-time check, Boeing spokesman Marc Birtel said.

The "service bulletin" Boeing was developing will target all similar 737 models with comparable flight cycle time as the Arizona jet, which was 15 years old and had about 39,000 takeoff and landing cycles, National Transportation Safety Board member Robert Sumwalt said.

The bulletin would outline extensive checks of two lines of "lap joints" that run the length of the fuselage. The NTSB has not mandated the checks, but Sumwalt said the Federal Aviation Administration is likely to make them mandatory.

The NTSB also could issue urgent recommendations for inspections on other 737s if investigators decide a problem has been overlooked. The FAA declined to say if it would require other operators to check their aircraft for similar flaws.

The cracks found in the three Southwest 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.

Two planes have been found with cracks similar to those in the Phoenix aircraft and will be evaluated and repaired before they are returned to service, Southwest said on Sunday in a prepared statement about its inspections. Sumwalt said a third plane had been found with cracks developing.

The NTSB planned a press briefing at 1:30 p.m. PT on Monday.

Previously, the riveted joints were not extensively checked because they were believed not susceptible to fatigue, Sumwalt said.

"Up to this point only visual inspections were required for 737s of this type because testing and analysis did not indicate that more extensive testing was necessary," Sumwalt said. That will likely change after Friday's incident, he said.

The tear along a riveted "lap joint" above the midsection of the plane shows evidence of extensive cracking that hadn't been discovered during routine maintenance

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