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Cracks found on three Southwest 737’s; Boeing planes Serice Bulletin
4 April 2011

The U.S. National Transportation Safety Board (NTSB) provided an update regarding the continuing investigation into the mid-air rupture of the fuselage skin on Southwest Airlines flight 812 that occurred on Friday, April 1st. The aircraft made an emergency landing in Yuma, Arizona.

On April 3, mechanics from Southwest Airlines, under the supervision of NTSB investigators, removed a section of the ruptured fuselage skin from Friday’s accident. The segment will be transported to NTSB headquarters in Washington, D.C. for in-depth analysis.

In addition, NTSB investigators conducted additional inspections of other portions of the lap joint along the fuselage of the accident airplane and found evidence of additional cracks.

The past few days, Southwest Airlines has been conducting additional non destructive testing inspections on 79 of their 737 airplanes. Additional crack indications in the lap joints have been identified on 3 airplanes.

The NTSB, along with the other investigative parties – FAA, Boeing, and Southwest Airlines – has been working to determine what actions might be necessary to inspect any similar airplanes.
As a result of the findings to date and the results of the Southwest Airlines inspections, Boeing has indicated that they will be drafting a Service Bulletin to describe the inspection techniques that they would recommend be accomplished on similar airplanes.

While the specifics of the Service Bulletin are being developed, the focus is to require inspection of the left and right lap joints on all similar 737 airplanes that have comparable cycles (takeoffs and landings) as the accident airplane. Once the Service Bulletin is released by Boeing, the FAA will make a determination whether to make it mandatory for all similar 737 airplanes.

A check by ASN of the Service Difficulty Reports of the accident airplane, N632SW, revealed that 38 reports were related to the Fuselage (cracks, damage, corrosion of for example stringer clips and frames).

About three of those reports were from roughly the fuselage section were the rupture occorred  (Body Station 685-727).

The last report is dated March 27 at an aircraft total time of 48722 hours and 39768 cycles.

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