Southwest jet had misaligned rivets

WASHINGTON, April 26 (UPI) -- Manufacturing problems may have been responsible for a gaping hole in the roof of a Southwest Airlines jetliner earlier this month, an investigation indicates.

A preliminary report by the National Transportation Safety Board revealed that dangerous structural cracks in the Boeing 737 jet's fuselage might have been due to misaligned rivet holes and loose bolts during manufacture.

The April 1 event occurred as the 15-year-old 737 jetliner was headed from Phoenix to Sacramento, Calif. with 122 people aboard.

The twin-engine plane experienced sudden cabin depressurization and was forced to make an emergency landing at a military base in Yuma, Ariz.

X-ray inspections of the plane found that several feet from the rupture, rivet holes in the upper and lower aluminum skin of the fuselage were "slightly offset relative to each other," the report said.

The NTSB report also said many of the rivet holes were found to be of irregular shape.

Along the actual tear, investigators discovered "fatigue cracks emanating from at least 42 of the 58 rivet holes."

The NTSB said Monday its examination of the rivets and holes is continuing along with a fatigue analysis of the aluminum skin.