There are, in fact, several airlines that permit use of mobile phones while in flight. OnAir is the provider of the service that they use. There are a number of carriers that have signed up and implemented the service, including BA, EK and RJ. And more are coming.

Similar to the WiFi services available in-flight they work because there is a repeater on the plane. By having the radio so close to the devices they can transmit at lower radio levels and things generally work just fine.

Not absolutely true.

A little EE knowledge can be a dangerous thing.

I will defer to others' knowledge on this. Let's say that it's usually true a device has to be close to interfere. My point is that when sitting in the cabin you are often a lot closer to avionic equipment than you may think.

However the basic laws of physics are what they are, and this does not change based on the perception of someone's level of knowledge. Distance matters. It is not the only determining factor, to be sure. But radiators further away will have less impact. Again, that's just physics.

As for RF propagation- it is not statistical. It is completely deterministic. Perhaps we can't model all of the different parameters at play, but that doesn't make the underlying process any less deterministic.

Cheers.

Let's agree that at 'close range' the signal is usually stronger,
and the possibility of interference increases. But sitting in a
long metal tube, after a certain small distance, the distance
does not really matter any more (unless the 'tube' is a mile
long or something).

And you right in your second point.

Inasmuch as electric field signal intensity diminishes with the square of the distance from the source, the distance matters substantially, even considering the channeling effects of the metal tube that might tend to confine the radiation axially (although the cross section of the plane is still reasonably large). One needn't have a tube anywhere that long to see substantial attenuation of the signal at the receiver, depending upon where it is located.

Cheers.

And Maxwell's equations govern 'DC to light'. I don't know if you
would call Maxwell's equations as "basic" laws of physics. They
are what they are. But do they help answer the question? No.
When have you used Maxwell to solve complex RF propogation
questions? Or used Maxwell without a supercomputer or an array
of computers?


Yes, distance matters for gross differences in distance, especially
when comparing 'close' to 'far'. But as you agree, distance is not
the only determining factor.


RF propogation has to be looked at statistically in any real-world
environment. You could say it is deterministic, and determined by
Maxwell's equations, but is it useful to say that?

One might say that quantum mechanics is deterministic too. This
may not be true, but knowledge of quantum mechanics or Maxwell
is usually not useful when many real-world factors are involved.


.

Am I missing something or have the experts weighing in on this thread not reached consensus? Is it possible the science isn't settled? Is this possibly one small battlefield in the war of the collectivists vs. the libertarians? Is there bias simply because so many of the people who yap loudly on their phones in confined spaces such as planes are so very annoying to begin with, (no FTers I hasten to add)? ;) I have to fess up to sometimes turning on the Bose before the double-dings have sounded. Still, after reading through the thread I'll continue to do what one pilot recently suggested here. :)

Cheers,
Fredd

Some people refuse to follow rules because they think think they're special or smarter than everyone else or have issues with authority that should be addressed through therapy.

+1 Amen

That's the result of poor shielding in your headphones.

Here are a few pro and cons from a pilot: http://www.gadling.com/2008/07/18/pl...-on-airplanes/

A researcher with 17 years of academic and government study realted to the topic: http://www.aviationtoday.com/av/issu...rence_952.html

NASA performed a series of tests on emissions from cellphones and other PEDs. See "Wireless Phone Threat Assessment and New Wireless Technology Concerns for Aircraft Navigation Radios," NASA/TP-2003-212446, July 2003; "Portable Wireless LAN Device and Two-Way Radio Threat Assessment for Aircraft Navigation Radios," NASA/TP-2003-212438, July 2003; "Evaluation of a Mobile Phone for Aircraft GPS Interference," NASA/TM-2004-213001, March 2004.

The National Telecommunications and Information Administration has performed two studies of potential interference with GPS from ultrawideband systems: "Assessment of Compatibility Between Ultrawideband (UWB) Systems and Global Positioning System (GPS) Receivers," Special Publication 01-45, U.S. Department of Commerce, February 2001; "Measurements to Determine Potential Interference to GPS Receivers From Ultrawideband Transmission Systems," Report 01-384, U.S. Department of Commerce, February 2001.

For more about electronic devices on aircraft, see the following: "Do Portable Electronics Endanger Flight?" IEEE Spectrum, September 1996; Bill Strauss and M. Granger Morgan, "Everyday Threats to Aircraft Safety," Issues in Science and Technology, pp. 82.86, Winter 2002.03; Bill Strauss, "Portable Electronic Devices Onboard Commercial Aircraft: Assessing the Risks," Ph.D. Thesis, Carnegie Mellon University, 2005.

(taken from http://spectrum.ieee.org/aerospace/a...any-airspeed/5)

Great links. Thanks.


From the first link:

The most frequently quoted study was done by Carnigie Mellon University in 2003.
Their comprehensive findings were summarized as follows:

The key conclusions were that
(1) onboard cellular telephone calls were observed in-flight and activity is appreciable;
(2) signal activity was observed in the aviation critical frequency bands at field strengths
capable of causing interference to onboard avionics; and
(3) onboard spectral activity was observed at flight critical phases.


The entire report is fascinating, but if you don't have the time to read it all,
here is a short interview with Bill Strauss, the person responsible for the report.
He found that 1/3 of the time cell phones were being used illegally inflight, their
frequencies actually crossed into the GPS band.

[continued]
The airline I currently work for decided to go through the long and costly process
to demonstrate to the FAA that cell phone use after landing and while taxiing to the
gate was safe.

The test involved filling every seat with a person using a cell phone from a variety
of manufacturers on each of the airplanes the airline operated.

Little regard was given to GPS and ground-based navigation interference, since
the airplane was simply taxiing to the gate. Subsequently, each airplane type at
the company passed, except for one. When this airplane, an Airbus, was tested, for
some reason the smoke detector in a lavatory would activate.

After further modifications, the FAA approved cell phone use while taxiing in for
each one of our aircraft types. I realize this is anecdotal, but it does represent
at least some sort of interference....


- - -

From the second link:

Avionics: You say there has been an interference problem for 40-plus years?

Strauss: It's closer to 50 at this point. Since the `50s and `60s timeframe, commercial
aviation has had interference problems with passenger electronics. You can actually find
the first regulation governing the issue in May of `61. That had to do with portable FM
radios affecting some of the older-type navigational aids, which weren't as sophisticated
and hardened to interference.

[continued]
Avionics: What else did you get from the ASRS data?

Strauss: One thing you get is some sense of the incidents' criticality. For example, the
pilot may have noticed some interference on his VOR, but it was a clear day, so he didn't
have to rely on the instrument. Then there are other cases where the pilots are relying
solely on instruments, and you have air traffic control saying, "You're five miles off
course."

The other thing that the ASRS data shows is which combination of PEDs and avionics seems
to be getting more incident reports. Basically, it said cellular phones and VOR was the
combination most reported. VOR was the primary navaid, certainly at the time I did the
study, in 2002, and most of the [ASRS] data is from the `90s. So you're not going to see
as much involving GPS. But we looked at GPS because we know that's where we're going.

Avionics: What did the ASRS data tell you about PED use during flight?

Strauss: We found that most reports of interference were during cruise, but there was a
significant number during departure and a lot during approach. The effect of cellular
phones on ILS systems was found to be significant, given the fact that people often use
their cell phones during the approach phase of flight.


- - -


Does anyone still belive there is no problem?


.

That is true in general, but not necessarily in specific situations. This is exactly why waveguides (for example, fiber optics) were invented - to allow radiation to propagate long distances without significant attenuation due to diffusion.

Deterministic and statistical are not mutually exclusive. Deterministic merely states that, knowing the exact initial conditions and the laws governing the evolution of the situation, the outcome at any time can be known. That does not mean that the initial conditions or factors in the intervening time will always be the same upon every trial, and moreover, because it is exceedingly (if not impossibly) difficult to know the exact initial conditions and guarantee all of the intervening conditions, knowing the final outcome is difficult or impossible in practice. Especially in chaotic systems, infinitesimal changes in the initial conditions can yield large changes in the final outcome, after sufficient timescales. This is exactly why, for example, weather forecasts are quoted in probabilities despite the fact that the weather is an entirely deterministic system.

When trying to predict the state of a system that is strongly dependent on initial conditions, or when trying to achieve great accuracy for that prediction regardless of the sensitivity on initial conditions, a statistical analysis is required. For this interference situation, a little bit of both factors (though mostly the second) apply.

Only for spherical isotropic emission from a point source. Dipole emission drops off even more rapidly, while beamed emission can drop off much more slowly; in vacuum, lasers (or other strongly-beamed, coherent sources) will attenuate incredibly slowly, depending on how well-constrained the beam spreading is. When waveguides are used (to artificially constrain beam spreading), vacuum attenuation can be negligible.

In this case, I will agree with you; microwave waveguides generally operate most efficiently when the waveguide dimensions are no more than a few wavelengths. Nevertheless, that is not the only effect to consider, and if the tube were of proper dimensions to be an efficient waveguide, its length would be far less relevant (as that is the entire purpose of a waveguide).

For many reasons, I think that cell phones and other properly functioning consumer electronics should not be a source of major interference with the avionic equipment (whether in the cockpit or elsewhere). The point here, however, is that it cannot be simply dismissed as due to "distance attenuation and miniscule emitted power" without considering all the factors properly. (GSM noise can be an issue for audio reception - as the wiring throughout the airplane acts as an enormous antenna for GSM noise - even if not for the avionics.)

There are several potential problems with in-flight cell phone systems
like OnAir:

1) Passengers will turn on their cell phones and make calls
even if they do not have GSM phones. There phones will
transmit at full power trying to reach the ground, and at
frequencies not expected by the aircraft's systems (which
were tested with GSM phones and the OnAir system.

2) Passengers with GSM phones will continue to use their
phones on approach and landing, after the OnAir system is
turned off. Again, lots of phones transmitting at full power.

3) Passengers will try to use their phones outside the EU
airspace where OnAir will be licensed. If OnAir is turned off,
once again all of those phones will transmit at full power.

4) Passengers will try to use their GSM phones even if they
don't have an international roaming service contract, or do
not want to pay for the OnAir service and make calls anyway.
Once again, possibly calls made at full power.


Once people get the idea that phone use is OK during flight,
they will assume it is Ok to use any phone and under any
circumstances - - either because they feel they can (and
know it may be improper), or by 'monkey-see-monkey-do'
ignorance.

And making calls is way more dangerous than a bunch of
people forgetting to turn off their cell phones during flight.
Making calls, especially at altitude, forces the cell phone
to transmit at (near) maximum power.


A cell phone, when not used but ON, will tranmit brief bursts
at intervals, so much less dangerous. A system like OnAir
will have close proximity to the cell phones onboard, so the
power levels from the system and the phones is much less
then when making regular calls.

Except, of course, in the situations mentioned above.

.