Mobile Phones

[Stephen Furner]

If you were planning to use your mobile phone in a light aircraft or microlight while in the air, how would you check on the ground that it will not cause interference with your aircrafts avionics?

Yes, I know that all CAA and Ofcom recommendations are not to use a mobile in the air unless its an emergency - life threatening – situation. Talking to pilots and passengers the reality is that there are many people out there currently doing this on a regular basis.

Let’s not go down the should you or shouldn’t you route, it’s an old and well rehearsed argument, but let’s look at what can be done to minimise any risk by identifying the checks to be made beforehand.

[IO540]

One could borrow an avionics tester (e.g. an IFR4000), turn the signal level down to the minimum at which the instruments don't quite flag out, and then play around with the phone.

Unless you have crap wiring/grounding (itself quite common in GA) you are unlikely to see any interference.

[Whopity]

You can quite often hear a phone in the aircraft on either the radio or intercom and it is identified by a rapid ticking noise when it sends packets of data. It can also go out on your transmission and be picked up by ATC. I have been told by ATC to tell my passenger to switch their phone off.

The bursts of data are more likely to be picked up by audio systems that rectify the RF, than any instrumentation.

Place you mobile near a BT phone and you will probably hear a similar noise.

[IO540]

Indeed, but I think this is caused by the phone's RF messing up the circuitry in the headset, or the mike.

That would not be suprising. I get that too, especially with the satellite phone.

But I have never seen interference with any VHF or UHF equipment.

Nevertheless, I switch off the satphone, and try to make sure all mobiles are switched off (and that includes the Ipad/3G :) ) if flying an ILS in IMC.

[Stephen Furner]

According to CAA PAPER 2003/3 “Effects of Interference from Cellular Telephones on Aircraft Avionic Equipment” the problems caused by a mobile phone 30 cm from an avionics and instrument panel are:


Compass froze or overshot actual magnetic bearing.
Instability of indicators.
Digital VOR navigation bearing display errors up to 5 degrees.
VOR navigation To/From indicator reversal.
VOR and ILS course deviation indicator errors with and without a failure flag.
Reduced sensitivity of the ILS Localiser receiver.
Background noise on audio outputs.

This was few years ago now so phone technology has moved on, even if most UK GA cockpits still date back 25 years or more.

When asking my question I had in mind some simple practical checks a pilot could make with just a mobile phone and observing its effects on the aircraft.

There are lots of adverts in the aviation magazines for headsets that have a capability for a Bluetooth connection to a mobile phone. I thought that maybe using one of these headsets or something similar, it would be possible to hold the phone in front of the avionics stack, or in various positions around the cockpit, while making and receiving a few test calls.

Observing the avionics behavior during the test calls might then give a rough indication of any potential interference problems?

[Shunter]

Compass froze or overshot actual magnetic bearing - NO.
Instability of indicators - NO.
Digital VOR navigation bearing display errors up to 5 degrees - NO.
VOR navigation To/From indicator reversal - NO.
VOR and ILS course deviation indicator errors with and without a failure flag - NO.
Reduced sensitivity of the ILS Localiser receiver - NO.
Background noise on audio outputs - YES, although nothing major.

That's purely a response from me in regard to my own aeroplane. I have considerable disdain for bad science, and have tried my level best to prove that any of these assertions hold any water by deliberating dialling my home line to maximise RF activity then shoving the phone as close to these "sensitive" instruments as possible. Nothing... absolutely nothing.

That said, as mentioned above I'm not a scientist and I'll keep them switched off during serious stuff, like flying instrument approaches. They are however very useful on a nice VMC day for calling a taxi from 20nm out.

[dublinpilot]

Is it possible that you could conduct a test as Shunter has done and find no problems, but change the frequency that the instrument is tuned to and all of a sudden find a problem?

The only problems I've seen were the audio described above, and something interferring with the compass, but can't remember if that was a mobile or something else.

dp

[777fly]

With the ever increasing use of FADEC to control your engine(s), how can you ever be sure that the emi from your mobile phone will not cause the digital electronic controllers to malfunction and power down or fail the engine on your GA aircraft, or even on the heavier metal? I'm sure that it's safe on traditional carb/magneto engines, but modern stuff? There's no knowing what the risk is at present. Better safe than sorry, until they check it all out.

[IO540]

Nothing in life is guaranteed (except death) but FADEC controls on big jet engines are built and tested to withstand electromagnetic radiation (both radiated and conducted) way in excess of anything that's required in industry.

It is obviously completely impossible (short of a strip search and confiscation) to make sure nobody on board has a mobile phone which is switched on. Or has some other electronic device which is radiating.

That said, I have far less faith in GA electronics than I have in the big stuff. I am an electronics engineer (35+ years' experience) and a lot of stuff that goes on in GA avionics is atrocious. A lot of the stuff is designed by complete muppets.

A friend of mine is on his 4th Aspen EFD1000, in 3 years. The last one died just outside the 1 year warranty so while they have supplied a replacement they have washed their hands of covering the labour. They suggested that there was a thunderstorm in the vicinity of his flight :yuk: So, yeah, there is an awful lot of crap out there, in the GA business.

[ExSp33db1rd]

If I was flying a Cat III ILS at night, into Zurich, with a 'glass cockpit' I might give this some thought, but I don't think your average, GA, recreational pilot has anything to worry about, enjoy the technology that allows you to call your girl-friend to be waiting for you as you land.

But if a student, don't start texting her before you've raised the flaps after landing - as one of mine did ! If I hadn't thought that I might damage some part of the airframe, I'd have hurled it, and him, out of the cockpit !

Damned phones, what was wrong with Morse Code ?

[flybymike]

I don't know how any of you guys can hear a damn thing from a mobile phone given the cacophany from the engine in the average light aircraft, nor for that matter, how the person at the other end can make out what you are saying either.

[ExSp33db1rd]

On the rare occasion I indulge ( only if I feel that I might have to ) I plug an earpiece and inline mic. into the thing and tuck the earpiece under my headset into my ear, then tell any caller that I'm flying, can't hear, will call back when I'm down, that usually shuts them up as they can't understand a word, but at least I know that the person I was probably expecting to call did so, and they know that I know and wasn't just ignoring them until such time as I choose to check my 'missed calls' (probably about once a week )

NOTHING ( or very rarely ) is anything that important, and it's only when it might be that I take the phone flying.

[IO540]

I don't know how any of you guys can hear a damn thing from a mobile phone given the cacophany from the engine in the average light aircraft, nor for that matter, how the person at the other end can make out what you are saying either.

Indeed, though there are headset adapters, and also bluetooth-capable aviation headsets (Zulu, Bose A20).

But the real issue is that the phone doesn't usually work above about 1000-2000ft.

Occassionally one can send a text message higher than that, and one often receives them much higher (it is normal to find "welcome to xxxx" messages from Belgium, Germany, Austria, Italy, Slovenia, Croatia upon landing following a flight mostly at FL140+). But one can't rely on it.

A satphone (http://www.peter2000.co.uk/aviation/satcomms/index.html) is the way to do texts, but then I find a lot of terrestrial networks do not receive them... However one can do short emails with it, which are more reliable. Its best use is for tafs/metars for various airports.

[Whopity]

phone technology has moved on,The major change in phone technology since the early days is that the RF output power has reduced considerably however; it is proportional to the received signal. This is a means of conserving battery power. The weaker the received signal, the higher the power of the transmitter, so when conducting tests, you will get different results depending upon the reception area you are in. You may have noted how, when leaving a phone unattended for a long period, the battery life is vary variable, and longer in a good signal area

[lopresto]

Never had problems with 2 iPhone and 1 iPad on board...

C172 nd Pa28 "old cockpit"
DA40 with G1000.

Ciao

[IO540]

Whopity is correct.

However the variable RF output cuts both ways, and aboard an aircraft at say 2000ft the received signal will be very poor, so the phone will wind its power output to maximum.

That's why phone battery life is usually much worse in the countryside :)

Also, most of the battery life improvements of the last decade or so have been achieved by discontinuous transmission, whereby the transmitter is cycled on/off. This also dramatically reduces the power radiated into one's brain.

They have also stretched out the interval between an inactive phone transmitting to contact the base station(s). It is now IIRC about 10 minutes. So if you have a phone just lying there, it will not radiate anything (of significant power) except for a second or two every 10 mins.

But despite all that, the peak power which a phone can put out is still as high as ever - 400mW I think, though the figure varies according to which frequency it is on (900/1800 etc).

If you want to see if a phone is interfering with avionics, you will need to do it in a low signal area, and actually make a call with it (or receive a call).

Much more common cases of avionics interference are VHF-GPS issues e.g. the 11th or 13th subharmonic of 1575MHz clobbering the GPS receiver. Try transmitting on 121.15MHz or around there and watch the GPS signal levels.

[Stephen Furner]

Some interesting and useful points made here about this idea of a simple check on the ground for mobile phone interference before using it in the air. From what’s said here my idea of a few simple ground checks in the cockpit is not sufficient on its own. These are a good first step but there are also some general guidelines/principles or perhaps a code of practice for the use of the phone in the air needed as well. This would be to cater for recommendations such as turn the phone off for an ILS approach in IMC, or if tuning into a weak VOR or DME then turn of the mobile to ensure maximum receiver sensitivity, or even students should not text until the aircraft is stationary in case they get thrown out of a moving aircraft by an enraged instructor.

[Whopity]

Much more common cases of avionics interference are VHF-GPS issuesOften overlooked is the fact that GPS invariably uses an active antenna i.e. it has a transistor amplifier built into the aerial. A strong signal saturates the transistor, regardless of frequency, and it becomes a switch and turns off the antenna.

[pilot2bornot2b...]

I remember watching a Mythbusters edition where they attempted to test this. You might find this interesting:

Annotated Mythbusters: Episode 49: Cellphones on Planes and Helium Raft (http://kwc.org/mythbusters/2006/04/episode_49_cellphones_on_plane.html)

[B2N2]

Let's not overthink this one.
Under VFR, make the call, you can't talk on the radio and on the phone at the same time anyway. I can garantee you that a cellphone does not effect a pitot static instrument such as altitude and airspeed. You can hold heading by looking outside. Make the call, done it numerous times.
The only restriction is your cell phone provider, my current one is not much good above 3000' AGL.

Under IFR ( and IMC) you shouldn't have time to chat on the phone with your buddies anyway :suspect: so unless it's an dire emergency I wouldn't do it.

If I have a total electrical failure I'll use my phone since there is nothing left to influence anyways...:E

[ExSp33db1rd]

B2N2

Most sense so far.

[LH2]

B2N2

Most sense so far.

I have to agree. Bloody American sense of pragmatism. :}

[niceday2700classic]

I'd say whilst flying VFR the risk is so minimal as to be non-existent. No-one seems to have been able to demonstrate any sort of interference, but even if there was some small effect then it shouldn't endanger a VFR flight. As someone else said, you hold your heading by looking outside.

I've found the practical altitude limit to be about 2,500 ft. But I'm sure it depends on the network, the model of phone and the location. So if any LARS unit wonders why someone reports descending 2,500 ft and then 2 mins later reports climbing back up then it was probably to get a text sent! :-)

The "tick, tick, tick" you hear when the phone is transmitting is not interference with the radio, it is the effect the phone has on the loudspeakers in your headset. You'll hear exactly the same thing if you place a phone which is 'doing something' near any other 'live' loudspeaker such as a small kitchen radio, a hi-fi, or indeed in the car. The ticking isn't a problem, it's just annoying.

[ShyTorque]

I flew one type of aircraft (helicopter, IFR twin, made in USA, quite a few of them about) for five years or so where a phone left switched on in the aft baggage bay would set off the smoke/fire detector. As the bay was not accessible in flight, and there was no fire extinguisher in there, there was no way of knowing if the warning was real or not. The required checklist drill was to land asap. Bad enough VMC but a big concern when IMC.

We obviously emphasised this issue to passengers during the safety brief.....

The aircraft manufacturer said they had found no problems on their side of the Atlantic. But of course their mobile phone network uses a different frequency band.

[FlyingKiwi_73]

this whole phone things B*LL*CKS
With the engine running and avionics on I showed a friend of mine what happens if i held my BB up to the VOR or NDB needles, nothing. near the radio, nothing not even interference on the headset. made a call to his phone. nothing.

I know thats not exactly a rigorous scientific test but seriously how is a bloke 10m back in business going to mess with the ILS when he's on the phone?

I think its more to do with paying attention to announcements etc while on board.

[madlandrover]

Were you airborne at the time? Experience with GA avionics in the UK shows that the interference of the phone finding cells is transmitted over RT calls. Rather annoying for all concerned.

[FlyingKiwi_73]

No i did this all on the ground.... don't like to be too distracted by doing this in the air.

I have had the phone in the cockpit and recieved many (missed) calls, (could not hear the ringer over the noise of the engine) and not noticed a blip. the radio by the bed tho, goes off when i get a txt!!

i think the sheilding is better in the cockpit.

[ExSp33db1rd]

Not totally relevant, but don't totally ignore interference from various sources, once had a compass problem on a 707, turned out it was a tape recorder - you know, the sort that were about the size of a portable typewriter and used reel to reel tape ( ask your dad ) - that had been loaded into the stowage above the seats - between two very large lines with the note : Do not load any electrical equipment here ! The permanent magnet in the loudspeaker was effecting some remote compass sensing stuff at that point.

Holding the phone near the ILS / VOR needles isn't the problem, hold the phone near the equipment that DRIVES those needles. Could be somewhere near where the phone is being used, as in my 707 case.

Murphy is always with us, but I agree, in small, VFR aircraft - no problem, just don't rest the phone on the glareshield, near the little compass suspended from the top of the windscreen !

[FlyingKiwi_73]

I take ExSp33db1rd's point, but the phone was in between the 'dail' and the radio stack.

Also those magnets were huge, and certainly can do some damage, i'm an IT geek by trade and have seen Harddrives sitting on large speaker stacks wiped (certainly corupted) by the magnets they contain.

As for the Mag Compass i was told don't even leave car keys near them!!!

[Stephen Furner]

How high will a cell phone work at? It can be a lot higher than the expected 2 to 3 thousand feet.

According to studies carried out in Canada for a single engine light aircraft it is possible - with great tenacity in the face of repeated failed call attempts - to get through up to around 7000ft or so http://physics911.net/pdf/Achilles.pdf (http://physics911.net/pdf/Achilles.pdf) As height increases the probability of getting a connection linearly decreases until at around 7 to 8 thousand feet it reaches zero.

[IO540]

It depends on where you are relative to the towers.

In the UK there is rarely a signal above 2k-3k.

In southern France, near the mountains, I was able to get a dial-up data call (for internet weather) at 8k. The call lasted maybe a few minutes.

I assume they had towers high up. In 2002 I saw people using mobile phones on top of Mt Kinabalu in Borneo after walking up there; 16000ft.

Never tried voice calls...

[stevelup]

That's over 10,000 feet with possible trees etc in the way! If I were in an aircraft, I could have un-interupted line of sight to the base station and could therefore pick up a slightly stronger signal.

That would be true if it wasn't for the fact that the cell towers are pretty directional and don't waste huge amounts of energy by pointlessly blasting radio waves towards the sky.

From two miles away (horizontally), you could get a perfect signal. At just a few hundred meters directly above the cell, you'll get nothing.

[172driver]

In southern France, near the mountains, I was able to get a dial-up data call (for internet weather) at 8k. The call lasted maybe a few minutes.

I assume they had towers high up.

Nope. AFAIK it has to do with the density of the towers. The problem is not the reception, but the 'lock on'. If there are many towers (as in the UK) the phone in your a/c cannot lock on to any one, as it is moving too fast. OTOH flying in sparsely populated areas (think central France, southern inland Spain) you usually get a signal at 8k.

Disclaimer: I am not a mobile phone engineer, the above from personal experience and reading a couple of articles on the subject.

[Stephen Furner]

Based on this discussion I have put together a short proposal for a simple check that a pilot could use to identify any very obvious interference in a GA aircraft's avionics. Assuming forewarned is forearmed I thought this might help manage down the risk from using the phone if it was necessary to make a call while operating the aircraft.

The proposal is a set of PowerPoint slides that I have loaded onto Facebook as an album at Mobile Phone Check | Facebook (http://www.facebook.com/media/set/?set=a.2094199590749.2106494.1118091118&l=7693f816c4&type=1)

[Lasiorhinus]

Plenty of headsets out there that connect to phones - and they're brilliant for getting AWISs from airports that for some bizzare reason have AWIS/AWIB available only by phone, not NDBs.
Also brilliant for mobile internet to get updated weather, weather radar, and submitting amended flight plans on the fly (so to speak).

Phone technology in Australia varies with the network. If you have a GSM phone, it won't work about about 3000 feet, but NextG antennas are not shielded downwards, so they work great at altitude.

Personally, ive made voice calls as high as 10,000 feet, and used mobile internet as high as 14,000 feet.

[WestWind1950]

Ther biggest issue and one the mobile phone companies do not like is when you are at altitude, your phone possibly can "see" and "be seen" by several base stations, all of which will try and respond to the handset! This can cause confusion on the network if a single handset suddenly appears in more than one location on the network!

This was the reason that mobiles were/are not allowed to be used in Germany... the LBA had a notice about it. That was some years ago and I'm not sure if that notice is out. Because of the speeds we fly and the altitudes we are at, the signal goes from one tower to the next and the system can get jammed.

I do know that some pilots got their mobiles blocked from the service provided because they were disturbing the network. It is NOT always what happens on the plane that the deal is, there could be other reasons for having them forbidden.