Federal accident investigators have determined that a manufacturing slip-up was responsible for a foot-long hole that opened up in the fuselage of an American Airlines Boeing 757 jet flying near Miami last October.
The National Transportation Safety Board issued its final report on the incident Tuesday, the eve of a public forum by the board examining the broad issue of structural problems affecting aging aircraft.
The report cites Boeing Co. for faulty production procedures that made the aircraft's aluminum skin too thin at the point where it ruptured in midair. None of the 160 people aboard suffered injuries when a 13-inch by 7-inch gash suddenly ripped open above the left front door of the 20-year old jet, resulting in rapid decompression of the cabin at 32,000 feet. The report indicates the pilots followed proper emergency procedures and the jet, en route from Miami to Boston, returned safely to the Miami International Airport.
Boeing has said it cooperated fully with the investigation. The company voluntarily issued a safety bulletin in November 2010, urging airlines to start inspecting certain parts of some 757s as frequently as after every 30 flights.
On Wednesday, the safety board kicked off a two-day session in Washington, D.C., focusing on enhanced inspection and maintenance requirements for older jetliners. Government and industry safety experts are slated to testify about new testing procedures and methods to reduce mistakes by mechanics when they check the structural integrity of aircraft.
For more than two decades, the Federal Aviation Administration and the airline industry have pursued various safety programs to ensure the structural soundness of older planes. But some of those efforts have come under public scrutiny recently, as a result of dramatic in-flight events such as the one that occurred over Miami a year ago.
In April, a five-foot hole opened up in the fuselage of a 15-year old Southwest Airlines Co. Boeing 737 jet while it was cruising over Arizona. The plane landed safely without serious injuries. But the safety board subsequently identified a number of manufacturing lapses that caused cracks and allowed them to grow undetected in the aluminum skin, leading to the dramatic rupture.
As a result, the FAA and foreign regulators ordered stepped-up inspections of certain Boeing 737 jets. But except for a small number of Southwest jets, those checks haven't found similar problems on 737 fleets flown by other carriers, according to industry officials. The safety board hasn't yet released a final report about the Arizona event.
According to Tuesday's report, the 757 operated by AMR Corp.'s American Airlines unit had accumulated more than 22,000 takeoffs prior to last year's emergency over Florida. The board found that certain sections of skin that had been chemically treated were slightly below the minimum thickness specified by Boeing, allowing cracks to start on the inside and spread through the aluminum.
The Miami incident prompted both Boeing and the FAA to call for stepped-up, repetitive structural inspections of specific 757 fuselage sections.
The safety board's report also cited two other Boeing 757s with the same "nonconforming thickness" material at the same location.
Six weeks before the Miami event, according to the board's report, a nearly foot-long crack was found on a United Airlines Boeing 757 "after reports of a whistling noise" during flight.
After the enhanced inspections kicked in, according the board, mechanics detected a second American Boeing 757 with cracks in the relevant fuselage sections.
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