Southwest grounds 2 more jets over cracks

By Jewel Samad, AFP/Getty Images

The 5-foot-long fuselage skin taken from the Southwest Airlines accident aircraft is shown at the National Transportation Safety Board in Washington, April 5.

EnlargeCloseBy Jewel Samad, AFP/Getty Images

The 5-foot-long fuselage skin taken from the Southwest Airlines accident aircraft is shown at the National Transportation Safety Board in Washington, April 5.

The airline said it discovered "minor subsurface cracking" on the aluminum skin on the Boeing 737-300s. The five jets have been taken out of service until Boeing can recommend how to repair them.

METAL FATIGUE: Experts say it is a rare riskAfter a weekend in which hundreds of its flights were canceled while the airline conducted inspections, Southwest said it has resumed normal service.

The inspections were triggered by an incident on Southwest Flight 812 from Phoenix to Sacramento. A 5-foot-long section of the aircraft's skin on the fuselage above the wing ripped open at 34,000 feet.

The sudden loss of cabin pressure forced the pilots to don oxygen masks and rapidly descend to lower altitudes. One flight attendant was injured, but none of the 118 passengers was hurt.

Investigators with the National Transportation Safety Board found a number of cracks on a line of rivets where two sections of the fuselage skin were connected. Those cracks appear to have weakened the skin, said NTSB board member Robert Sumwalt.

The discovery prompted the Federal Aviation Administration (FAA) and Boeing to require inspections on a small portion of the 737 fleet manufactured during the 1980s and 1990s. Out of the 80 such planes operated in the United States, Southwest owns 78. Alaska Airlines flies the other two.

NTSB Chairman Debbie Hersman said she was "very pleased" by the rapid response to the incident by Southwest, Boeing and the FAA.

The agency displayed the section of torn fuselage at its Washington, D.C., metals lab Tuesday. The jet's skin tore along a line of rivets that ran from the front to the rear of the jet, leaving a jagged edge flapping loose above the upper fuselage.

Southwest completed inspections of the 737-300s covered by the FAA before the agency could issue the formal order. "With our knowledge of what the FAA had planned, we believe the

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NTSB: Cracks found in 3 grounded Southwest planes

officials said.

"What we saw with Flight 812 was a new and unknown issue," said Mike Van de Ven, Southwest executive vice president and chief operating officer. He said the airline had complied with federally mandated and Boeing-recommended inspections for the plane.

Federal records show cracks were found and repaired a year ago in the frame of the same Southwest plane.

A March 2010 inspection found 10 instances of cracking in the frame, which is part of the fuselage, and another 11 instances of cracked stringer clips, which help hold the plane's skin on, according to an AP review of FAA records of maintenance problems.

The records for the plane show the cracks were either repaired or the damaged parts replaced. Cracking accounted for a majority of the 28 problem reports filed as a result of that inspection.

It's common for fuselage cracks to be found during inspections of aging planes, especially during scheduled heavy-maintenance checks in which planes are taken apart so that inspectors can see into areas not normally visible.

The Arizona jetliner had gone through about 39,000 cycles of pressurizing, generally a count of takeoffs and landings. Cracks can develop from the constant cycle of pressurizing for flight, then releasing the pressure.

Southwest officials said the plane was given a routine inspection Tuesday and underwent its last so-called heavy check, a more costly and extensive overhaul, in March 2010.

The decompression happened about 18 minutes after takeoff from Phoenix Sky Harbor International Airport.

At cruising altitude of some 34,000 feet, the pilots declared an emergency and briefly considered returning to Phoenix before the cabin crew told them of the extent of the damage, Sumwalt said. The plane's voice and data recorders were being examined in Washington.

Southwest operates about 170 of the 737-300s in its fleet of 548 planes, but it replaced the aluminum skin on many of the 300s in recent years, a spokeswoman said. The planes that were grounded over the weekend have not had their skin replaced.

US Airways operates 18 of the older-model 737-300s, but the company said Monday it has been told by Boeing that its jets aren't affected.

Lufthansa has a fleet of 63 Boeing 737s, including 33 of the 300 series. But just three of those are from the same series as the Southwest jet.

"As a precautionary measure, all three aircraft underwent additional checks over the weekend, which didn't yield any further findings. Accordingly, the aircraft are operating as scheduled," said airline spokesman Martin Riecken. "We are in close contact with Boeing regarding this issue and are awaiting further advice from the manufacturer."

In July 2009, a football-sized hole opened up in-flight in the fuselage of another of Southwest's Boeing 737s, depressurizing the cabin. Sumwalt said the two incidents appeared to be unrelated.

A fuselage failure, although extremely rare, can have deadly consequences. In 1988, cracks caused part of the roof of an Aloha Airlines Boeing 737 to peel open while the jet flew from Hilo to Honolulu. The flight attendant died, and dozens of passengers were injured.

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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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