Manufacturing Defect Led to 737 Depressurization Incident

AINsafety » October 14, 2013
This diagram shows how the fuselage skin of a Boeing 737 was damaged by incorrect installation of a fuselage crown skin panel.
October 14, 2013, 6:00 PM

The National Transportation Safety Board (NTSB) has concluded that the improper installation of a fuselage crown skin panel during the manufacturing process was the probable cause of substantial damage to a Southwest Airlines Boeing 737 during a rapid decompression incident in April 2011. According to a report released on September 23, the error resulted in damage fatigue cracking in a number of locations and the eventual failure of the skin panel.

The 737, carrying 122 people, was climbing through FL340 at 15:58 local time when an eight-inch by 60-inch section of the aircraft’s upper fuselage skin fractured and peeled back. The crew performed an emergency descent and landed the aircraft safely at Yuma International Airport in Arizona. Two people, including one flight attendant, were treated for minor injuries.

The final report said the entire section of fuselage skin remained attached along the lower edge and was deformed outward. There were some abrasion marks on the fuselage skin below the forward edge of the hole and the fracture appeared along the upper edge through a lap joint. During the post-accident skin repair, two cracked stringer clips were also identified.

According to NTSB investigators, contributing to the injuries of one of the people taken to hospital was a flight attendant’s failure to follow procedures requiring immediate donning of an oxygen mask when cabin pressure is lost. He lost consciousness and broke his nose when he hit a bulkhead. The FAA’s Advisory Circular 61-107B says a person’s time of useful consciousness at FL340 is approximately 30 seconds.

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