THE USE of mobile phones in aircraft isn鈥檛 really dangerous鈥攁t least,
that鈥檚 what the conspiracy theorists believe. They reckon that the ruling on
in-flight phone calls is just a way for airlines to make you use their own
pricey cellular telephone systems.
In the US, a Congressional subcommittee grilled airline representatives and
regulators about the issue last month. But the committee heard that using
cellphones in planes may indeed pose a risk, albeit a slight one.
This would seem to vindicate the treatment of Manchester oil worker Neil
Whitehouse, who was sentenced last summer to a year in jail by a British court
for refusing to turn off his mobile phone on a flight home from Madrid. Although
he was only typing a message to be sent on landing, not actually making a call,
the court decided that he was putting the flight at risk.
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The potential for problems is certainly there. Modern airliners are packed
with electronic devices that control the plane and handle navigation and
communications. Each has to meet stringent safeguards to make sure it doesn鈥檛
emit radiation that would interfere with other devices in the
plane鈥攕tandards that passengers鈥� personal electronic devices don鈥檛
necessarily meet. Emissions from inside the plane could also interfere with
sensitive antennae on the outside.
The in-flight cellphones operated by airlines at a heart-stopping $6 a
minute are designed to meet the same safety criteria as other on-board devices.
They radiate their signal from a dedicated antenna on the outside of the
plane.
But despite running a number of studies, Boeing, Airbus and various
government agencies haven鈥檛 been able to find clear evidence of problems caused
by personal electronic devices, including mobile phones.
No impact
鈥淲e鈥檝e done our own studies. We鈥檝e found cellphones actually have no impact
on the navigation system,鈥� says Maryanne Greczyn, a spokeswoman for Airbus
Industries of North America in Herndon, Virginia. Nor do they affect other
critical systems, she says. The only impact Airbus found? 鈥淪ometimes when a
passenger is starting or finishing a phone call, the pilot hears a very slight
beep in the headset,鈥� she says.
The best evidence yet of a problem comes from a report released this year by
Britain鈥檚 Civil Aviation Authority (27 May, p 7). Its researchers generated
simulated cellphone transmissions inside two Boeing aircraft. They concluded
that the transmissions could create signals at a power and frequency that
would not affect the latest equipment, but exceeded the safety threshold
established in 1984 and might therefore affect some of the older equipment on
board. This doesn鈥檛 mean 鈥渕ission critical鈥� equipment such as the navigation
system and flight controls. But the devices that could be affected, such as
smoke detectors and fuel level indicators, could still create serious problems
for the flight crew if they malfunction.
Many planes still use equipment certified to the older standards, says Dan
Hawkes, head of avionics at the CAA鈥檚 Safety Regulation Group. The CAA study
doesn鈥檛 prove the equipment will actually fail when subjected to the signals,
but does show there鈥檚 a danger. 鈥淲e鈥檝e taken some of the uncertainty out of
these beliefs,鈥� he says. Another study later this year will see if the cellphone
signals actually cause devices to fail.
In 1996, RTCA, a consultant hired by the Federal Aviation Administration in
the US to conduct tests, determined that potential problems from personal
electronic devices were 鈥渓ow鈥�. Nevertheless, it recommended a ban on their use
during 鈥渃ritical鈥� periods of flight, such as take-off and landing. RTCA didn鈥檛
actually test cellphones, but nevertheless recommended their wholesale ban on
flights.
But if 鈥渂etter safe than sorry鈥� is the current policy, it鈥檚 applied
inconsistently, according to Marshall Cross, the chairman of MegaWave
Corporation, based in Boylston, Massachusetts. Why are cellphones outlawed when
no one considers a ban on laptops? 鈥淚t鈥檚 like most things in life. The reason is
a little bit technical, a little bit economic and a little bit political,鈥� says
Cross.
The company wrote a report for the FAA in 1998 saying it is possible to build
an on-board system that can detect dangerous signals from electronic devices.
But Cross鈥檚 personal conclusion is that mobile phones aren鈥檛 the real threat.
鈥淵ou鈥檇 have to stretch things pretty far to figure out how a cellphone could
interfere with a plane鈥檚 systems,鈥� he says.
Cellphones transmit in ranges of around 400, 800 or 1800 megahertz. Since no
important piece of aircraft equipment operates at those frequencies, the
possibility of interference is very low, Cross says.
The use of computers and electronic game systems is much more worrying, he
says. They can generate very strong signals at frequencies that could interfere
with plane electronics, especially if a mouse is attached (the wire operates as
an antenna) or if their built-in shielding is somehow damaged. Some airlines are
even planning to put sockets for laptops in seatbacks.
There鈥檚 fairly convincing anecdotal evidence that some personal electronic
devices have interfered with systems. Air crew on one flight found that the
autopilot was being disconnected, and narrowed the problem down to a passenger鈥檚
portable computer. They could actually watch the autopilot disconnect when they
switched the computer on. Boeing bought the computer, took it to the airline鈥檚
labs and even tested it on an empty flight. But as with every other reported
instance of interference, technicians were unable to replicate the problem.
Some engineers, however, such as Bruce Donham of Boeing, say that common
sense suggests phones are more risky than laptops. 鈥淎 device capable of
producing a strong emission is not as safe as a device which does not have any
intentional emission,鈥� he says. Nevertheless, many experts think it鈥檚 illogical
that cellphones are prohibited when computers aren鈥檛.
Dangerous signals
Besides, the problem is more complicated than simply looking at power and
frequency. In the air, the plane operates in a soup of electronic emissions,
created by its own electronics and by ground-based radiation. Electronic devices
in the cabin鈥攅specially those emitting a strong signal鈥攃an behave
unpredictably, reinforcing other signals, for instance, or creating unforeseen
harmonics that disrupt systems.
Despite the Congressional subcommittee hearings last month, no one seems to
be working seriously on a technical solution that would allow passengers to use
their phones. That鈥檚 mostly because no one 鈥攂esides cellphone users
themselves鈥攕tands to gain a lot if the phones are allowed in the air. Even
the cellphone companies don鈥檛 want it. They are concerned that airborne signals
could cause problems by flooding a number of the networks鈥� base stations at once
with the same signal. This effect, called bigfooting, happens because airborne
cellphone signals tend to go to many base stations at once, unlike land calls
which usually go to just one or two stations. In the US, even if FAA regulations
didn鈥檛 prohibit cellphones in the air, Federal Communications Commission
regulations would.
Possible solutions might be to enhance airliners鈥� electronic insulation, or
to fit detectors which warned flight staff when passenger devices were emitting
dangerous signals. But Cross complains that neither the FAA, the airlines nor
the manufacturers are showing much interest in developing these.
So despite Congressional suspicions and the occasional irritated (or jailed)
mobile user, the industry鈥檚 鈥渂etter safe than sorry鈥� policy on mobile phones
seems likely to continue. In the absence of firm evidence that the international
airline industry is engaged in a vast conspiracy to overcharge its customers, a
delayed phone call seems a small price to pay for even the tiniest reduction in
the chances of a plane crash.
But you鈥檒l still be allowed to use your personal computer during a flight.
And while that remains the case, airlines can hardly claim that logic has
prevailed.