Posted on 10/29/2004 7:19:07 AM PDT by safisoft
WASHINGTON Boeing Co., working with federal safety officials, is investigating tiny scratches on some older-model planes to see whether the marks are evidence of a potentially dangerous problem with the jets' outer shells.
The scratches, or scribe marks, occur when a plane is prepared for repainting, Boeing spokesman Jim Proulx said. Workers scrape off a sealant used on the joints that hold together sections of the aircraft's aluminum skin, he said.
The scribe marks can lead to deeper cracks that can spread, potentially leading to an uncontrolled decompression that can strip off pieces of the skin, according to a Federal Aviation Administration safety bulletin issued late last year.
Proulx said Boeing would issue a bulletin to airlines later this year telling them to inspect planes once they had taken off and landed about 4,500 times after being repainted. An inspection involves taking off the paint along the joints to make sure there is no scribing, he said.
The FAA is considering following up with an order to inspect repainted planes and repair them if cracks are found, agency spokeswoman Diane Spitaliere said.
The problem came to light during routine maintenance last October, Spitaliere said. Inspections began on about 80 aging jets that had been painted in the last few years, she said. Two have been found to have cracks.
About 60 Boeing planes have been found to have scribe marks, Proulx said. The vast majority are 737s, the world's most popular plane, with about 2,800 in service. The 737s tend to be older - and to have been repainted more often - than other aircraft.
Also found to have the scribe marks were a few 747s, one 757 and one 767, Proulx said. The carriers themselves conducted most of the inspections.
Planes found with scribe marks were permitted back in service but must be inspected every 250 flight hours to make sure the scratches do not become cracks, Spitaliere said. For the hardworking 737, that means about once a month.
These marks can be a stress concentration and lead to a crack under fatigue loads.
In many metals, surface scratches can also initiate stress-induced localized corrosion...
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