FAA orders checks on bolts of Boeing 737s

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Tuesday, April 11, 2000, 09:25 p.m. Pacific

Checks ordered on bolts of Boeing 737s

by Chuck Taylor Seattle Times aerospace reporter Loose nuts found on 10 in-service 737s, a defect the government says could lead to loss of control of an airplane, prompted the Federal Aviation Administration to issue an airworthiness directive yesterday ordering inspections to ensure certain bolts were tightened properly in the factory.

The problem is the latest in a string of quality-control issues at Boeing's commercial-airplane factories. Since September, other loose nuts and bolts, substandard fasteners and other shortcomings have prompted an FAA audit of the company and heightened scrutiny of suppliers.

In the most recent defect traced to assembly, loose nuts have been found in a mechanism on "next generation" Boeing 737s that moves a crucial control surface on the plane's tail.

The production problem was made public by the FAA's directive, published in yesterday's Federal Register, but Boeing and airlines have known about it for months.

Boeing sent an urgent service bulletin to airlines Feb. 14 recommending inspections after it received the first report of a loose nut in a linkage that moves the 737's elevators. Elevators are flaps on the trailing edge of the horizontal stabilizer, the small winglike portion of the tail, and are used to direct a plane's nose up or down, for climbing or descending.

The nuts and bolts are connected to a power-control unit (PCU) that moves the elevator. If a nut came off, the result could be "loss of control of the airplane during takeoff and landing," the FAA directive states.

That doesn't necessarily mean a plane would crash, but among the hundreds of airworthiness directives issued every year, loss of control is among the more serious consequences cited when the FAA addresses a determined "unsafe condition" with an inspection or repair order.

`Fleet's in pretty good shape'

In all, 10 of 333 737s inspected so far had loose nuts, said Boeing spokeswoman Shannon Myers. There are 482 planes in the worldwide fleet of affected 737-600s, -700s and -800s, so the status of 149 planes appears to be unknown.

"We really feel like the fleet has been inspected, and we think our fleet's in pretty good shape," Myers said, calling the problem isolated.

In the airworthiness directive, the FAA said loose nuts "had been finger-tightened but had not been properly torqued," or tightened.

The FAA order makes the Boeing-recommended inspections mandatory for an estimated 224 airplanes registered in the U.S., if the inspections haven't been done voluntarily. It requires airlines to report any problems they find and sets a May 25 deadline. Foreign regulators are likely to follow the FAA's lead.

There are about 480 next-generation 737-600s, -700s and -800s in service worldwide. Those refined models of the world's most popular jetliner have been in production at Boeing's Renton factory since 1996 and in service since 1997.

After the first report of a loose nut, Boeing checked planes on the assembly line in Renton and found no problems, Myers said.

More-stringent inspections

It's not clear why the loose nuts escaped scrutiny during the assembly process, Myers said. Boeing has imposed a more-stringent inspection to ensure these particular nuts and bolts are tightened properly.

The loose nuts are only the latest in a series of quality problems in Boeing factories:

In September, bolts that attach the vertical stabilizer, or fin, to the fuselage of 767s were discovered not tightened properly on one in-service plane and others still in the Everett factory.

In November, the company disclosed that plastic drip shields, which protect flight-deck components from dribbles of condensation, and fiberglass air ducts that did not meet flammability standards had been installed on hundreds of in-service airplanes of various models.

A corrosion-inhibiting coating applied to fuel-tank access doors was found to be flaking, creating the potential for fuel contamination. The affected doors were installed in a year's worth of all Boeing planes, except models added to Boeing's lineup from its acquisition of McDonnell Douglas.

In March, the company said a supplier had disclosed that a number of shipments of fasteners did not meet specifications. Boeing determined that about 20 in-service planes could be affected.

Also last month, Boeing discovered a crack in a beam called a stringer as it was being installed on a 767-300 and determined that it and 31 other identical parts for other planes had not been heat-treated by the supplier.

An FAA audit of Boeing's quality-control programs was begun in December, and findings are being prepared for release this summer. But the agency already has told Boeing to improve its oversight of the quality of parts supplied by outside companies.

http://www.seattletimes.com/news/business/html98/bolt11_20000411.html

-- Martin Thompson (mthom1927@aol.com), April 11, 2000

Answers

I don't understand. Can computer malfunctions knock bolts loose? I suppose with all the vibration of aircraft, this, along with almost anything else, is possible.

-- Loner (loner@bigfoot.com), April 11, 2000.

Think of all the looseness we've been hearing about the last few months, in things like aircraft stabilizer bars, air conditioning equipment, etc. In previous years I practically never heard of this kind of problem. I think computer controls have much to do with it.

-- Billiver (billiver@aol.com), April 11, 2000.

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