Probe into hole in plane turns to Boeing assembly process

Investigators trying to determine why the roof of a Southwest Airlines jet peeled open in flight this month are focusing on the manufacturing process at Boeing.

Government and industry officials say investigators noticed that the stricken jet and five other Southwest planes that had cracks in their metal skins were all built at about the same time in the same Boeing plant.

The officials cautioned Monday that no final determination has been made about why the planes developed cracks in an area of the fuselage many years before Boeing expected to see problems.

A 5-foot hole tore open in the roof of the Southwest Boeing 737 as Flight 812 climbed to 34,000 feet above Arizona on April 1. The pilot guided the plane to a safe emergency landing, and there were no serious injuries.

Metal fatigue was initially suspected to have caused tiny subsurface cracks in the aluminum skin, which gave way during flight. Now investigators think the seeds of the near-disaster might have been planted when the plane was built.

Officials said investigators are looking at several possible mistakes during assembly, including the size and the way rivets and sealants were used to hold aluminum panels together on the plane's roof.

The National Transportation Safety Board is leading the investigation. A spokesman for the agency declined to comment.

Possible problems with the planes' production were first reported by ABC News.

After the Southwest incident, Boeing told airlines that owned about 190 other 737s built in the 1990s to immediately conduct electromagnetic inspections of an area of the roof called the lap joint, where overlapping panels of skin are riveted together.

Chicago-based Boeing Co. said Monday that inspections have been completed on about three-fourths of those planes, and only the five at Southwest were found to have cracks. Boeing said it was analyzing portions from panels of those planes "to validate the initial inspection findings," but added no final conclusions have been drawn.

The Southwest plane had made about 39,000 flights. A senior Boeing engineer said this month that the company didn't expect airlines would need to inspect the lap joints for metal fatigue until about 60,000 flights.

Southwest declined to comment. Flight 812 was the second Southwest jet to develop a hole in the roof in the past three years. The airline canceled nearly 700 flights this month after grounding 79 similar planes — one-seventh of its fleet — for inspections.

Last week, Southwest Airlines Co. CEO Gary Kelly said he saw no evidence that bookings had been hurt by the incident. Kelly, whose airline flies only 737s and is one of Boeing's biggest customers, went out of his way to praise the aircraft maker's speedy response, including designing repair jobs.