Manufacturing Issues Suspected in Southwest Jet Rupture

>> Sunday, April 24, 2011


Investigators increasingly are focused on manufacturing-related issues, rather than a possible design flaw by Boeing Co., as they strive to unravel what caused the midair fuselage rupture of a Southwest Airlines Co. jet earlier this month, according to government and industry officials.

The officials said it's too early to draw definitive conclusions, and National Transportation Safety Board investigators haven't issued any statements hinting at what they suspect. But areas that federal and industry experts are examining as part of the probe, according to these officials, include riveting techniques, fixtures used to hold parts of the planes during assembly and uses of sealants on the 15-year-old Boeing 737.

The plane suffered a rapid decompression and had a five-foot gash rip open in the upper part of its cabin, about four feet above the windows, while cruising at about 34,000 feet.

Nobody was seriously hurt and the twin-engine jet, with 122 people aboard, made an emergency landing at a military base in Arizona on April 1. But the incident prompted Southwest to temporarily ground and inspect 79 of its other older Boeing 737s, and it also sparked a round of swift inspections of about 100 additional aging Boeing 737 models worldwide.

Four other Southwest jets were found to have fuselage cracks requiring repairs, but at this point no similar problems have been discovered on other airline fleets.

The primary reason for emphasizing potential manufacturing-related lapses or problems, according to these officials, stems from the fact that a number of the Southwest planes with fuselage cracks were built around the same time. And jets flown by other carriers, even some with a larger number of takeoffs and landings that the Southwest plane with the hole, haven't shown any signs of structural weakness or fatigue.

So far, according to one official familiar with the investigation, investigators have spent the most effort to understand the manufacturing history of the Southwest planes that had significant cracking of their aluminum skins. The plane with the rupture had logged about 39,000 takeoffs and landings, substantially fewer than the point at which Boeing experts anticipated it could face serious metal fatigue.

But according to officials familiar with the investigation, it's still too early to know whether the suspect Southwest jets illustrate a possible quality-control or manufacturing problem of relatively short duration, or some other potential causes.

The stresses planes undergo each time their cabins pressurize and then depressurize during a trip are major factors in creating cracks and possibly causing metal fatigue.

Possible production problems were first reported on Saturday by ABC news.

Federal Aviation Administration chief Randy Babbitt previously suggested that production issues were under heightened scrutiny. He told an industry conference in Miami earlier this month that the agency, among other things, was looking into "manufacturing techniques" along with Boeing. Mr. Babbitt said agency experts were examining existing aging-aircraft inspection rules and seeking to determine "are we looking at the right things?"

Eventually, more than 400 additional older 737 jets will have to be inspected around the globe, as a result of safety mandates by the FAA and foreign regulators.

On Saturday a Southwest spokeswoman declined to comment on the investigation. She said the incident plane was still undergoing repairs, but the five others identified with cracks have been fixed and were returned to service.

Boeing officials have said that the particular fuselage design on the affected airplanes was changed when a new version of the model was introduced in 1993. The so-called 737 "Next Generation" is the type still being built today and Boeing has delivered more than 3,500 of those, according to company data.

The safety mandates issued by the FAA cover certain 737-300, 737-400 and 737-500 versions, and they kick in based on the number of takeoffs and landings planes have logged.

Over the years, the FAA and industry have developed a comprehensive set of inspection standards and procedures to identify and repair fuselage cracks on older planes before they can result in major problems. The April Southwest incident shocked the airline industry, surprised regulators and spooked many travelers because until it happened, Boeing had concluded that the plane didn't need to undergo detailed structural inspections on that part of its fuselage until much later in its life.

The planes under scrutiny feature a certain type of "lap joint" -- the area where Boeing and government investigators have said the structural cracks originated -- and surrounding strengtheners designed to prevent cracks from growing.

The twin-engine 737, the company's most popular jet and a workhorse for carriers around the globe, first entered service in 1968. Since then, the more than 6,600 have been completed at Boeing's factory in Renton, Wash., just south of Seattle, and more than 2,000 remain on order. The planes requiring inspection were built between 1993 and 2000.

Before reaching Washington state, however, 737 fuselage barrels are assembled at a factory in Wichita, Kan. That facility, now owned by Spirit AeroSystems Holdings Inc., a major aerospace supplier, was at the time a wholly-owned Boeing factory. Boeing spun off its commercial airplanes unit in Wichita in 2005.

On Friday, Boeing said it continues to work closely with the safety board and the FAA to determine what caused the April 1 event.

In its statement, the Chicago aerospace giant said that "to date, inspections have been completed worldwide on approximately 75 percent of the 190 airplanes affected" by mandatory inspection rules, and only the handful of Southwest planes have "shown small subsurface cracks." "Portions of the panels from those airplanes have been shipped to Boeing, and we are conducting analyses to validate the initial inspection findings."

According to Boeing, "no conclusions have been reached about the root cause of the inspection findings" or how they may relate to the April 1 event, and "any attempt to draw conclusions on either would be premature and speculative."


Post a Comment