A raft of fastener problems continue to plague Boeing in
aircraft ranging from the 737 workhorse used by airlines such as Southwest to
the Dreamliner 787, whose rollout
has been delayed yet one more time.
In the most recent glitch, a pressurization test on a
Dreamliner fuselage revealed a small gap under the heads of thousands of
fasteners. The problem occurred on the floor grid and other structures
installed inside the fuselage shell where titanium was fastened to carbon
fiber composite.
It appears the engineering problem will require Boeing to
replace as many as 8,000 fasteners on 12 Dreamliners being assembled now.
Previously, Boeing blamed suppliers for a variety of
fastener problems that slowed the Dreamliner program. It appears though that
the newest failure results from poorly worded or inaccurate specifications on
how to attach titanium to the composite shell, according to an engineering
source at a Boeing supplier.
In a quote published by the Aero-News Network, Joy Romero,
vice president of Vought's 787 program and head of the Charleston, SC
plant where the rear fuselage sections are assembled, said "I don't think it
should be pushed on the inexperience of the mechanics. It's more about the
clarity of the specifications and the confusion of the specifications."
The specifications were developed by Boeing engineering
staff.
Before the end of the year, Boeing is expected to announce a
new Dreamliner delivery schedule incorporating both the strike delay and the
fastener issues. Boeing has already pushed back Dreamliner deliveries three
times and is expected to announce another timetable by the end of the year.
In another fastener debacle first reported
by Design News Nov. 25, defective nut plates were installed in 737s. It has
since been disclosed that the same bad parts have also been used in 747s, 767s
and 777s.
Deliveries of 737s and other aircraft are 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." Boeing plans to inspect 394 of the 737s
already in service.
"We continue to work the issues. Neither is an immediate safety-of-flight
issue," says Boeing Communications Official Bev Holland.
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 10 and 30 microns.
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.
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