pax use of electronic equipment

[Homer_J]

Part of my companys PA goes along the lines of "electronic equipment may interfere with the aircraft systems and can only be used when the seatbelt sign is turned off".

I was wondering why?

I guess its not because using your laptop interferes with the seatbelt sign, which was my first thought.
Is it because they don't want you listening to your ipod or playing solitaire during takeoff and landing when, if anything is
going to go wrong, they want your full attention.

Also......something else I've noticed recently.

Flying in VMC. Theres a cloud ahead. We fly through the cloud. As we pass through the cloud(and it only seems to happen above 220 ias) the wind noise in the cockpit seems to increase. Ok, sure coluds are water vapour and therefore more dense than thin air, but surly there not that dense.

[Conan The Barber]

Do a search here and all shall be revealed.

Clouds denser than air? Did you happen to notice the string then?

[PAXboy]

This question is asked about four times a year and a thread is running in PAX & SLF. :rolleyes:

[Halfbaked_Boy]

I always thought clouds (water vapour) were less dense than air... hence them being in suspense.

Cheers, Jack.

[Old Smokey]

Yes, this is an old one that's been done to death in other forums, having been a contributor myself. In the last decade, with much lower power outputs from computers, mobile phones etc., the problem seemed to be going away, but it hasn't. I was considering initiating a whole new thread for a recently encountered problem, but thank youHomer_J, you did it for me.

I was very recently operating a flight to India, and encountered severe interferance on the VHF frequency in use (133.8), to such extent that frequency change was necessary, and, at a later time when 133.8 was the only VHF frequency, had to resort to HF. Complaint to ATC that they were unreadable, and that the interferance was coming from an obvious series of mobile phone calls, had no response as no-one else was having a problem. We were the only affected aircraft, which obviously meant that the interferance was coming from within our own aircraft. We could hear the phone conversation with considerable clarity.

I had the cabin crew conduct a search, and sure enough, found the culprit who was using a 'state of the art' phone. I'm not au fait with current models, but it was referred to as either a blackberry, or blueberry.

The interferance caused was total, but seemed isolated to just that one VHF frequency, 133.8. After the offender ceased his third phone call, the problem stopped.

The problem was diminishing, it's back.

With respect to the cloud noise, it was common on the DC9 to hear a 'screeching' sound when passing through Cirrus cloud. I never had verification, but common folk-lore had it that it was caused by impact with ice crystals. Maybe so, maybe not.

Regards,

Old Smokey

[iakobos]

We could hear the phone conversation with considerable clarity.
I guess you are well aware that your COM decodes analog AM only and that a cellphone sends digital signals....in a frequency band at least 7 times higher and not even as a single stream on one specific frequency.

The location (and height) of the a/c at the the time of the interference might provide some clue.

[Old Smokey]

iakobos,

Thanks for the info, I know next to nothing about the characteristics of mobile phone operation, however, the interferance was genuine, as was the dial tones and conversation. At first we (the F/O and I) thought that it was the ATC controller having a private conversation whilst she was at work, but this appears not to have been so.

The location was just after Kuala Lumpur (almost overhead) to 200 nm Northwest of Kuala Lumpur. We were at 32000 feet, and the interferance only occurred on 133.8, a harmonic perhaps?

I'd be interested if you can do any detective work on this, it was not just nuisance value, it totally jammed the frequency.

Regards,

Old Smokey

[FakePilot]

I've seen frequency shifts with AM signals, i.e. a microphone cable hooked to am amp received a radio station quite well.
There's also stories of people's fillings and ROCKS received AM radio signals.
However I don't see how FM or a digital signal could be decoded by an AM device.
Old cell phone systems were FM, I'm pretty sure.

So it's odd you could have heard the message.

But never say never! All it takes it the right configuration of metal and just about any signal can do neat tricks.

[iakobos]

Less younger Smokey,

Both the distance/time length (close to 200nm), route and altitude of the a/c, and intelligibility of the reception make cellular as the cause of "interference" a no-go.

At first glance, and if the "dial tones" were actually dialing tones (DTMF), I could suggest so-called "long range telephones" which are indeed widely used in that part of the world.

These mid- to high power "telephones" are actually full duplex radios (10 to 50W and more), operating in the 30-50MHz bands, which in "hot" regions can provide communications over very long distances (especially early morning and early evening), talking several hundreds of miles here.
In many cases it is a point-to-point (private) radio network, i.e. a private wireless telephone network, with or without an interconnection to the regular public telephone.

I could well imagine a timber company linking its HQ with its remote locations.

The worst harmonic is usually the 3rd one.... 44.6 x 3 = guess what

[Old Smokey]

iakobos,

The worst harmonic is usually the 3rd one.... 44.6 x 3 = guess what
Even in my advancing years my mental arithmatic still says 44.6 X 3 = 133.8

It was indeed early evening, and it was a NOT so private wireless telephone network - The F/O and I speak 5 langauges between us, but it took a Hindi speaking Cabin Crew to translate for us. The latter made identification of the culprit (an Indian) so much easier.

These forums are marvellous, we have a lot of collective knowledge between us, we live and learn every day - Thank you.

Regards,

Older and Wiser Smokey

[iakobos]

You're welcome

I hope I helped save the ass of some future Blackberry users at cruise level.
Those crews can be rough at times... ;)

Disclaimer
My posts are in no way promoting or justifying the usage of cellphones or any other transmission-intended device on board an airplane.

If you see the cockpit crew handling a cellphone, it is because they are testing some instruments.

[derekl]

Interesting.

I'm with iakobos on this one.

I can't see how a BlackBerry (a digital cellphone) could turn up on 133.8, less still how the voice would be decoded by an AM airband (analogue) receiver.

The Blackberry (just a digital phone with extra bits) would be using GSM/GPRS which is a lightly-encrypted time-division multiplexed digital signal at 900MHz or higher. Ther is no way that you heard it in the clear in 133.8 MHz AM.

If it were a U.S. device, it might just have been a CDMA phone (code-division multiple access) -- same frequency bands, even less likely to be decoded as it's a spread-spectrum signal. But it wouldn't work outside the U.S.

You CAN decode FM signals on AM radio receivers by an effect known as "slope detection" -- but not digital signals.

[Self Loading Freight]

It might not have been the transmitter in the Blackberry per se - the phone will be doing some audio processing and there's a chance that a circuit using RF as part of that processing will be modulated somehow and something leaked.

Doesn't seem likely, but it's at least possible. Ideally, the errant device would have been confiscated and despatched to a competent authority for analysis!

R

[iakobos]

It is somewhere between extremely improbable and absolutely impossible.

Even if we assume that a "leak" could pop up somehow at 133.8 MHz, we have to do with 3V (?) circuits using digital technique.

I think no explanation could be found in interfering (as in "blocking out") with the plenty of microVolts received from the ATC signal and the detection by an AM receiver.

A leak would be "heard" as noise and be in the tenths of microWatt level, only detectable by lab equipment with a physical (or very near-) connection to the culprit.

[NeoDude]

Could it be possible that the person was using a hands free mic/speaker that was using the VHF band?

[Pegasus77]

In the A340 you can sometimes hear that you're flying through clouds, especially at a high IAS and a lower level (ie around FL200-250). Could be the ice crystals, no clue about that.

P77

[iakobos]

Quite unlikely, that kind of equipment is reserved for Santa Claus and only to be used during mid-winter season.
There is an exception to this though, it is allowed for pub-to-pub celebrations in Edinburgh when the local team crushes the Rangers.
Hib Hib Hurray !

Sorry....could not resist ;)

Unless it is a bluetooth device (very low power, much high frequency and again not analog), I do not see a speaker/mike having a transmitting capability.

[Old Smokey]

iakobos,

Thank you for your very informed responses. My knowledge of current generation personal communications systems is almost NIL, I can operate my mobile phone in voice and text mode, and that's my limit.

Further checking with the In Flight Supervisor confirms that the "offender" was indeed using a blackberry. After warning, the calls, and the interferance ceased immediately. I don't know a blackberry from a raspberry ripple.

I'd like to get to the bottom o0f this, further checking locally indicates that blackberry sales and use are soaring, and there may well be further repetitions of this event.

The FACTS are -

(1) The offender was using a "blackberry",
(2) The VHF com frequency affected was 133.8, all other frequencies were unaffected
(3) Dial tones, ring tones, and clear voice communications were clearly audible
(4) Reception from ATC on 133.8 was totally blocked, other ATC officers on other frequencies reported that our transmissions on 133.8 and their frequencies were unaffected.

Various responses, including your own iakobos, indicate that the possibility of this occurance is extremely unlikely. Well, be assured that there is no exaggeration in the facts given above.

Unless this is an extremely remote freak occurance, I firmly believe (now) that all mobile phones should be retained at the time of passenger security screening, and returned at the end of the flight. In our case, it caused a severe communications problem, bad enough, but what if the next personal communications "gadget" interferes with the ILS equipment? A total failure of such would be a nuisance, erroneous indications could be disastrous.

I speak as one who was always very sceptical of the mobile phone "menace", I'm now a total convert.

Good work iakobos,

Regards,

Old Smokey

[iakobos]

Smokey,

We will of course not come to a clear conclusion in this specific case, but just for the sake of it, let me think...

(1) the suspected pax used a blackberry

(2) only the channel called 133.8 seemed affected (in fact a window of a few KHz)

(3) all transmissions were clearly audible

(4) the interference (in this case perhaps appropriately called jamming) totally drowned ATC

Point 3 is evidence that the digital transmission from a berry (whatever sort) cannot be the cause, at least all by itself. There is nothing that can incidentally convert a digital signal into analog.

Point 4 shows that the signal was significantly stronger than ATC's, itself in essence strong (50W - line of sight).
This again cancels the berry-track, as far as the radiation of undesired harmonics or other spurious is concerned (much too weak).

I would add a point
(5) the interference took place at cruise level and lasted several minutes
Again this does not point toward a cellphone. It is possible to initiate a call under certain circumstances, but placing several calls and thereby maintaining minutes-long contact with ground cells is extremely improbable.

I might have the beginning of a small idea, but can you detail:

where was the pax sitting
front/mid/back ? and window or other seat ?

in your estimation, how long did the interference last ?

[Self Loading Freight]

Have you talked to RIM (Research In Motion, the people behind the Blackberry)? A look at the circuit diagram might reveal some plausible fault conditions that could generate the signal under discussion. I've known power supplies that could jam television signals, and FM radios that acted as rather efficient bugs due to microphony in the local oscillator - stuff can go wrong in some amazing ways.

R