Fastener problems continue to affect Boeing.
Deliveries of 737s are
now being delayed as Boeing replaces
nut plates that had been installed on the aircraft since August 2007.
Specifications require the nut plates to have an anti-corrosive cadmium
coating. For reasons that aren't clear, coated and uncoated nut plates were
intermingled in bins, making it difficult for assemblers to pull the right
parts. The problem was discovered last August at a Spirit AeroSystems factory
in Wichita, KS. The assembly plant provides fuselage and
wing components for Boeing aircraft.
The nut plates are used to fasten bundles of wires and other
parts to the inside of fuselages. There are thousands in every aircraft. According
to one source, fewer than 30 percent of the nut plates installed since August,
2007 are defective.
"We're replacing them as we find them," Boeing spokeswoman
Vicki Ray told the Associated Press. "Also to be addressed is the in-service
fleet, and we're still working on a plan for that." She says the defective
fasteners are not an immediate safety risk. Boeing plans to inspect 394 of the
737s already in service.
Cadmium
coatings are applied to ferrous and nonferrous metals to provide resistance to
corrosion. Like zinc, cadmium also provides sacrificial protection to a
substrate such as steel by being preferentially corroded when the coating is
damaged and small areas of the substrate are exposed. Electroplating accounts
for more than 90 percent of all cadmium used in coatings, and is normally
specified in thicknesses between 5 and 25 mm.
The Boeing Materials Group did pioneering work on the use of
cadmium coatings in aircraft all the way back to the 1960s. Significant work
has been conducted on replacing the toxic cadmium in recent years, but the
recent problem at Boeing was strictly a supply chain error.
As previously reported in Design News, fastener shortages
were a major problem in the early production ramp-up of the Dreamliner
787 program. At first, there was just a shortage of fasteners. Later, it
was reported by Boeing that there also were installation problems. Some of the
fasteners in the Dreamliners were not flush, and there was a gap between the
structure and the head of the fastener, according to Boeing spokeswoman Mary
Hansen. Another problem: The fastener's
pin was at times the incorrect length.
"We're going to remove and replace every one and work
with our partners to get this fixed as quickly and effectively as
possible," Hansen said.
The Federal Aviation Administration issued a new directive
in August about the need for more inspections of a fastener problem affecting
cargo doors on 747s.
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