SEATTLE -- The Boeing Co. acknowledged making a faulty repair in 1978 on the aft bulkhead of the Japanese Airlines 747 that crashed into a mountain in Japan last month, but does not know if the repair was a factor in the accident that killed all but four of the 524 people aboard.
The company also said Friday in a notice to all airlines flying 747s that the crash investigation indicates 'a decompression occurred during the flight due to a rupture' of the bulkhead.
But the company said further investigation was necessary before it can be determined if the faulty repair was a factor in the crash.
Boeing told the airlines the continuing inspection of the world's 747 fleet since the JAL crash and the crash of an Air-India 747 off the coast of Ireland in June, which killed 329 people, has revealed no inherent problems in the aircraft.
'There is no evidence that would suggest any problem with the basic design, manufacture or structural integrity of the 747 model aircraft,' Boeing said in its advisory.
Theories about what caused the JAL 747 to lose control and crash into the mountain have focused on the plane's rear bulkhead.
Investigators believe pressurized air blasted through an opening in the bulkhead, blowing the tail apart and sending the plane went out of control.
Large sections of the tail were found in the sea 80 miles from the crash site.
In a notice Friday to all airlines operating 747s, Boeing reported that a splice plate in the bulkhead was incorrectly assembled by a Boeing repair crew after a rough landing in 1978.
But the company disputed a published report Friday that the problem involved a single line of rivets instead of the double-line mandated by the plane's manual.
'We examined the aft pressure bulkhead at the site of the crash of Flight 123 and determined that a relatively small section of the bulkhead splice, approximately 17 percent of it, was not correctly assembled during a repair which Boeing made after a 1978 landing incident,' the company advisory said.
'Contrary to published reports, this mis-assembly does not involve a missing row of rivets. A splice plate added during the repair was incorrectly installed in this small section of the bulkhead splice such that one of three rows of rivets did not pass through the splice plate.'
Two Boeing metallurgists are in Japan with U.S. officials 'to obtain replicas or impressions of the fractured surfaces in this small section of the bulkhead splice before the wreckage is removed from the crash site,' the company said.
'These replicas will be analyzed to determine whether or not this repair contributed to the accident.'