By Dominic Gates
Seattle Times aerospace reporter
October 6, 2005
For more than two years, U.S. airplane passengers have flown more
securely because high-tech cockpit doors created a barrier to prevent
a repeat of 9/11, when terrorists entered the cockpit and commandeered
But, the doors were not foolproof.
In December 2003, a Northwest Airlines maintenance mechanic inside an
Airbus A330 jet on the ground in Minneapolis pushed the microphone
button to talk into his handheld radio. Though he hadn't touched the
cockpit door, he heard the sound of its lock operating.
Radio interference from his walkie-talkie had scrambled the
electronics inside the door's locking mechanism.
The discovery sparked a secretive and expensive engineering effort
that started with Airbus and eventually hit Boeing, and is only now
The security glitch affected all A330 and A340 jets - about 400 - that
had installed an Airbus-designed fortified door.
In May 2004, Boeing learned from three airline customers that it, too,
had the same problem, affecting some 1,700 jets. All Boeing
wide-bodies with fortified cockpit doors designed by the jet maker
Boeing and Airbus insist there was no immediate danger. The mechanic
had to be standing in precise spots with a particular walkie-talkie
tuned to a specific frequency and with a certain signal strength.
"It's an extraordinarily limited issue," said Airbus spokeswoman Mary
Federal Aviation Administration spokeswoman Laura Brown said the
agency was unable to replicate the problem on airplanes in flight.
Regardless, top experts at both airplane manufacturers have spent
nearly two years working quietly with the FAA to redesign the door
Boeing completed fixing the latches on all its affected jets last
The FAA this week is expected to issue an airworthiness directive, a
formal, after-the-fact order to all U.S. registered airlines with
Boeing jets that they must install a fix designed by Boeing.
All affected Airbus jets registered in the United States, about 20
airplanes, were fixed by September 2004.
"All the foreign carriers that fly [into the U.S.] are fixed, too,"
She said the FAA did not issue an airworthiness directive for Airbus
because so few jets in the U.S. were affected.
Airbus' Greczyn said last week the fix is now "nearly completed" on
all affected jets worldwide.
Four months after 9/11, the FAA mandated that cockpit doors on all
jets flying in the U.S. be strengthened.
The design demands were extraordinarily tricky. The doors had to be
strong enough to withstand bullets, yet engineered to burst open to
avoid a catastrophic twisting of the airframe in the event of a sudden
loss of cabin pressure.
The airlines had just 15 months to change the doors on about 7,000
U.S.-operated aircraft and some 2,000 foreign-owned.
Boeing and Airbus each developed designs using door-locking mechanisms
from a California supplier.
In both cases, the cockpit door is secured by aluminum rods that slide
into the lock or unlock positions when activated by an electronic
signal. Rapid decompression would also unlock the door.
A technical expert familiar with the intricacies of radio frequency,
or RF, agreed to discuss the interference issue on condition he not be
identified. He works for the government and believes he could lose his
job for speaking publicly about a sensitive security topic, even in
The expert said it is difficult to build any electronic product that's
protected from radio interference in a wide range of frequency bands.
He said a door controller is typically activated via a numeric code,
which produces an electronic signal to unlock the door. A
strong-enough external signal of the right frequency flooding the
circuit could fool the mechanism into thinking it was the "unlock the
"The world is filled with RF signals, and lots of times signals mix.
It's mathematically feasible to come up with a combination of
frequencies that could mix just enough to be right on target," said
the expert. "The world of RF is black magic."
The expert expressed concern that if "an educated electrical engineer
with a terrorist mind twist" could get hold of a door-lock controller,
it might be possible to reverse-engineer the mechanism and find the
frequency that would unlock it.
"It wouldn't take long to break down an engineering formula," the
expert said. "It could be done in 30 minutes."
But the chief engineer who led Boeing's effort to fix the problem on
its jets said the interference happens only in very narrow
circumstances, and that even an electronics expert would have great
difficulty exploiting this vulnerability. Boeing asked that the
engineer not be named to ensure his personal safety.
"I'd have to have equipment. I'd have to get it through security. I'd
have to know the right channel," the chief engineer said.
"I'd need to know quite a lot about where parts are installed on the
airplane. I'd need to do a lot of things I couldn't actually do" on a
When Boeing first learned of the issue last year, the FAA issued a
secret security-sensitive airworthiness directive alerting airlines.
After initially coming up with a quick fix, Boeing decided to go for a
longer-term, more-robust solution developed in cooperation with a top
FAA specialist based in Seattle.
Team worked in secrecy
A team of about five engineers secretly worked on the problem for more
than a year.
"We deliberately kept the wraps on it within Boeing," the chief
engineer said. "If people didn't need to know, they didn't know."
Boeing did not provide an estimate of the costs.
"Cost didn't come into it," said the chief engineer. "My concern was
making sure we got a good technical solution."
Originally, airlines paid $29,000 for each of the Airbus wide-body
door kits and between $40,000 and $100,000 for the Boeing wide-body
kits, depending on the plane's model and configuration.
The government provided a $97 million subsidy to defray costs, about
$13,000 per door.
The FAA tested and certified both door designs; the tests failed to
reveal the radio frequency interference issue.
"We did testing for every scenario you can imagine," the FAA's Brown
said. "You don't know what you don't know."
Airbus supplied the majority of fortified doors in its own aircraft,
and Boeing won 60 percent of the market to install the fortified doors
in its jets.
After the glitch was discovered, the FAA examined the doors made by
third-party vendors and found no similar interference problem.
Both Boeing and Airbus used the same supplier, Adams Rite Aerospace of
Fullerton, Calif., for their in-house door control.
Supplier passed tests
Airbus' Greczyn and Boeing spokesman Jim Proulx both stressed the
supplier had met certification requirements and passed the
interference tests then in place.
Executives at Adams Rite did not return repeated calls or respond to
e-mail requests for comment.
Following the scramble to fix the electronic locks, both plane makers
are also providing a backup option.
Boeing already had provided a manual bolt lock as a backup. A pilot
could use it in case of a perceived threat.
Airbus does not install a mechanical backup lock as standard.
But as a result of the locking incident, Greczyn said "a mechanical
backup ... has been designed and certified and is available to
customers to apply at their discretion."
Copyright =A9 2005 The Seattle Times Company
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