Mobile Myths?

[Foxcotte]

I'm kind of new at this professional aviation lark, so forgive me if this is a repeat question but I'm bugged enough about it to ask anyway!

I know the official story about mobile phones on aircraft "Please turn it off or it may affect the aircraft systems etc" but what is the REAL reason for authorities wanting people to switch their mobiles off? Okay the bandied answer is that the mobile signal may affect the increasingly sensitive aircraft systems, but I have heard a more plausible explanation in the case of a fast moving aircraft (passenger and mobile included) the mobile phone signal attempting to relay to the nearest comm relay satellite gets confused with the speed and attempts to relay to more than one sat - thus seriously clogging up the airways. With several satellites being clogged up with a fast moving mobile relay, some serious money on ground by the phone operators are lost - hence the request on so called safety grounds to switch the irritating little beast off. I haven't progressed to a fly-by-wire aircraft so in the primitive ones I do fly, mobile phones have absolutely NO affect on any of my not-so-sensitive instruments/systems other than to be a mild distraction to an eavesdropping pilot.

I'd be very interested if anyone out there can come up with a convincing, simple yet technical reason for the "switch off".

Just a further thought to ponder, if a mobile signal may affect an aircraft's systems, what about all the many heartbreaking mobile phone calls that were made from the four airliners on 9/11?? There were distinctly other reasons why these four aircraft headed earthwards and it doesn't seem to have been related to all the phone calls on board??

[Someone Else]

Its official mobile phones don't interfere with aircraft systems! Boeing proved it first, now Airbus have done the same.
Both manufacturers have signed deals with GlobalStar to relay calls via GlobalStar's satelites from small basestations mounted in the passenger cabin.
Expect the announcement to change radically once this revenue gathering opportunity becomes available to airlines.
Users will be brought to earth suddenly when they see the roaming charges on their next bill.

[Bealzebub]

Always fascinating to hear the opinions of the armchair experts.

There is evidence to suggest mobile phones may have interfered with aircraft systems, and if you search the CAA aeronautical information circulars on this subject, you can read them for yourselves. One point you might want to consider is that an aircraft structure has a vast array of transmitting and receiving aerials built into it. The architecture of the aircraft is such that the placement of these devices is designed to prevent cross interference between the receivers/transmitters and each other and with other sensitive aircraft systems. It doesn't take a huge amount of common sense (even from the most ardent conspiracy seekers) to realise that the introduction of additional mobile random tranceivers into this environment is likely to prove disprutive on many levels.

From my own experience the sound of loud mobile phone search signals in my headset whilst taxying at a busy airport is very distracting. It is therefore unacceptable. In addition is very unlikely that a mobile phone ( cellphone) will successfully aquire a signal in cruise flight despite increasing its output strength in an attempt to try. Potential disruption to communications or other systems ( however small) is most certainly undesirable during the climb, descent and approach phases of flight. During these phases most airlines will also restrict the use of other small electrical devices ( computers/CD players etc).

As regards sept 11th, I think you will find that many domestic airliners in the US are fitted with seatback flight phones. It was from these that calls were made. These phones are built into the electronic architecture of the aircraft and are therefore certified for use during flight. That notwithstanding such a catastophic event lends precious little arguement to the suggestion that mobile phones do not cause interference.

On a positive note, there seems to be some serious development of technology that may permit the use ( albeit perhaps limited ) of mobile phones at some point in the future. It would of course be unacceptable for a passenger to be using any device that distracts from the ability of the user or those around him to properly monitor such things as safety briefings.Any advances in the technology will therefore have to satisfy the regulatory authorities in all respects.

[cessna l plate]

OK, as a former mobile phone engineer for Cellnet, here is the deal.

There is liitle evidence to suggest that a phone will intefere with aircraft systems, as far as there is little to suggest that making a call in a petrol station will result in your anhialation. The probability is small, but would you really want to find out????

The "real" reason has already been given, albeit in the usual sort of sensational language that one reserves for jounalistts. Contrary to popular beleif, when you make a call, it does not go blasting off to the nearest satellite, neither does it scramble your brain.

It works like this. When you make a call, the phone samples what you say upto 7 times per second, and transmits this as a data stream to the network at a rate of 9600 bps. (At the other end, the computer fills in the gaps, and it sounds like you again) To enable this transmission to succeed at this rate, the phone will either speed up or slow down the transmission speed, so that when the signal gets to the network, it is travelling at 9600bps.
The speeding up or slowing down is dependent on where you are in realtion to a cellsite. ( A network receiving station) Due to this, the phone has a maximum range of about 10 kilometers. Beyond this, the signal reaches the cellsite too slowly, and the person at the other end thinks they are talking to a dalek. Too far away, and the computer cannot cope anymore, and drops the call altogether.

Now then, the cellsites are designed, as are the phones, for a land based existence. However, as I am sure you can all remeber from your R/T studies, radio waves move in all directions, and this inculdes UP. Because the ground is littered with cellsites, and don't forget that the "line of sight" rules apply in the main, even with a mobile phone, there is plenty of coverage at ground level, and the system can cope with a phone that can see 3 or 4 sites. Go up a few thousand feet, and the phone can now see hundreds of sites, and tries to talk to them all at once. Result, as has already been said, the network will go on strike tout suite.

Hope this clears it up.

[jetfour]

Let's get this straight.

Mobile phones work through ground stations only. Hence all the masts and elements strapped to buildings. A phone inside the aircraft will be busting its little gut to access a cell outside.

Satellite phones are still rare beasts and work exclusivly to/from satellites in earth orbit.

The two are very different.

The signals from the former will eminate from inside the aircraft, whilst the latter will send/receive via elements on the outer skin of the aircraft.

The CAA study did produce effects on aircraft instruments but was not exhaustive.

Radio signals are strange beasties. Have you ever been on a local frequency in summer and heard stations many, many hundreds of miles distant?

Murphy is still at his work. The wrong phone in the wrong place in an aircraft will, eventually do a nasty.

Would you like to be the one to find out?

[West Coast]

"Its official mobile phones don't interfere with aircraft systems!"


Really?

They are suspected to give false alarms on certain types of smoke detectors in cargo holds. Enough of a problem that Bombardier puts a caution note in the FCOM about it.

[Foxcotte]

Okay, I'm not sure what I've read is entirely conclusive yet, but it does begin to fill in some answers to the questions I've had.

I agree that mobile phones in the headphones are a bloody nuisance, but its always puzzled me why such strict rules about them on board. I agree I don't want to be the pilot who DOES find out what a mischievious mobile phone signal might do the aircraft I'm flying, but if it is in doubt (and I find that hard to believe in this day & age of anyone suing anyone for anything that the airlines/aircraft companies/mobile phone makers/mobile phone operators haven't tested this extensively already) why are phones allowed on board at all? Surely if there is some doubt - then switch them off & put them in the hold or a titanium sealed strong box in the cabin or whatever.

It does sound like the issue is more what the phone does elsewhere than granny calling to wish you bon voyage is actually going to turn the airbus upside down? Or Boeing for that matter. Presumably this matter is only going to affect the more sensitive aircraft around - if its an old banger with pulleys/cables and brute force to fly it - how can a mobile phone signal affect it? Fly-by-wire, glass cockpits and autopilots - yes, I can see the potential.

I'm certainly curious to see if this announcement is going to make things clearer or not?!!

Thanks for the answers so far ....:ok:

[PAXboy]

It has oft been said that 'a' mobile/cell phone will not affect a/c systems. However, if the a/c is operating (in any mode of flight or taxi) when 50% of the pax switch on their phones, then the combined singnals may have a cumulative affect. You can range the percentage and size of a/c to suit your level of concern. This is not my view but one that I have seen reported.

Better not to use them. Having a few minutes more of peace is worth it. Besides, even if late and needing to make an urgent call, the time that it takes to get from the a/c to local transport has always been enough time to make the call and explain the delay - in my experience.

We need radeng on this thread, he is a RAdio ENGineer.

--------------------
"I tell you, we are here on Earth to fart around, and don't let anybody tell you any different." Kurt Vonnegut, Jr.

[ft]

For crying out loud... they determined that mobile phones inside aircraft could cause nodes of radiated energy strong enough to break through the shielding of the aircraft systems.

I have no idea how they solve it with cell networks onboard. One fact is that the phones will never have to transmit at their maximum energy levels that way, as they would trying to reach a ground station from FL330 through the hull.

Fly-by-wire or tubes and fabric... both will have the risk of having an accident increase by a factor of eight, or if it was twelve, if a cellphone disturbs the ILS receiver so that the crew fly an NDB approach instead.

"I have my mobile on all the time and it never causes anything". Wrongo. You never observe anything it causes. Big difference.

Regards,
Fred

[Kolibear]

The Engineer magazine, this week (24/10 Page7 ) carried the following article (cut & pasted from their website

The Engineer (http://www.e4engineering.com/engineer/story.aspx?uid=2c6b23fa-c6f6-49fb-9f0d-eb7ee4c79aed&type=news)


From The Engineer, 24 September 2004


Project gives air play to mobiles
A two-year investigation by Airbus has revealed that mobile phones can be used on aircraft without interfering with the planes' systems.
During the EC-backed project, Airbus installed a picocell on an A320 which created a small mobile phone cell within the aircraft.
Calls were then routed to mobile and fixed phones on the ground via Globalstar satellites. Airbus also tested wireless systems such as Bluetooth, Wi-Fi and CDMA.
As a result the company plans to install in-flight mobile phone technology on its aircraft by 2006.
American Airlines is working on a similar technology to be introduced at around the same time, while Boeing has set up Connexion, which already operates wireless networking technology on commercial flights.

[Captain Airclues]

A mobile phone can set off the fire alarm on a simulator which then knocks off the motion in a rather violent way. I've seen it happen (it wan't mine, honest!).

Airclues

[Lowtimer]

Foxcotte,

I find that hard to believe in this day & age of anyone suing anyone for anything that the airlines/aircraft companies/mobile phone makers/mobile phone operators haven't tested this extensively already

a) You are forgetting that the majority of airliners out there were designed and built before mobile phones were commonplace, so this never arose in the design specs.

b) mobile phone operators do NOT want people doing more than 120 knots trying to operate on ground-based networks with ordinary mobile handsets, the doppler effect and the cell swamping effect cause real problems, so why do tests which would encourage people to try?

c) If the airlines could enforce taking people's mobiles away from them quickly and efficiently, without massive upset, they would. But you try separating peopel from their phones and see how far you get. Alternatively, see the bear trap you open up when trying to reunite a hundred-plus 400 p*ssed-off commuters with the correct mobile phones at the end of a flight on a tight turn-around

d) it's not just the transmissions: if a phone rings, with a vibrating alert, it creates a pretty hefty magnetic field. Even on a low-tech Cherokee I've seen this affect the compass. The passenger turned off his phone pretty quickly (I should have checked more thoroughly before departure).