a CD Player can bring down an airliner?
Join Date: Sep 2002
Location: NevadaUSA
Posts: 1
Likes: 0
Received 0 Likes
on
0 Posts
I remember reading a few articles concerning electronic equipment on aircraft a few years ago, and If I remember correctly, the main culprit is not RF based as much as EM. I'm definitely not an electronic whiz (far from it - when I cut a wire I tie the ends together so the electricity doesn't leak out) but the articles talked about the magnetic field generated by electric and electronic devices when turned on. These magnetic fields can interact (say two laptops are turned on and are in close proximity, two or three gameboys, etc.) and can nulify each other or amplify each other causing 2IM, 3IM interference and the like. The magnetic fields can then infringe on the fields generated not so much from the instruments, antennas, etc., but the cabling between the two, which usually runs much closer to the cabin.
The articles talked about the lack of adequate shielding of most consumer electronic devices causing all of this, and since it's a real impossibility to test all devices in every combination, we have the restrictions currently in place. Concerning laptops, the articles did say that most of them do have shielding built in, thus they are allowed where simple toys are not.
The articles talked about the lack of adequate shielding of most consumer electronic devices causing all of this, and since it's a real impossibility to test all devices in every combination, we have the restrictions currently in place. Concerning laptops, the articles did say that most of them do have shielding built in, thus they are allowed where simple toys are not.
411A - a very valid point regarding proper equipment and cable shielding.
But were your 7 passengers using analogue or digital phones? Because it is the digital pulses generated from phones which seems to cause the most - and the weirdest - problems. I have a cheap small colour TV in the kitchen - and if my digital cellphone rings, the TV will switch itself on and display odd screen captions which don't appear anywhere in the instruction leaflet! Digital phones can also cause strange buzzing sounds over car stereo systems unless a proper hands-free kit is fitted.....
I had one of the first GSM phones which I used in an 'airliner type' flight drck on the ground on many occasions with never any problems. But it was an old wires and clockwork dials flight deck - not a full-glass. Quite probably the problems caused by digital phones interfering with some aircraft systems simply aren't fully known - hence the ban on phones being switched on in airliners.
I flew a little PA28 with FM-immune King radios the other day - one of the passengers (despite my instruction) had forgotten to switch of his GSM phone and the frequent 'hand shake' pulses could be heard interfering with thee intercomm. Nothing else was affected - but the problem posed by passenger phones shouldn't be underestimated.
But were your 7 passengers using analogue or digital phones? Because it is the digital pulses generated from phones which seems to cause the most - and the weirdest - problems. I have a cheap small colour TV in the kitchen - and if my digital cellphone rings, the TV will switch itself on and display odd screen captions which don't appear anywhere in the instruction leaflet! Digital phones can also cause strange buzzing sounds over car stereo systems unless a proper hands-free kit is fitted.....
I had one of the first GSM phones which I used in an 'airliner type' flight drck on the ground on many occasions with never any problems. But it was an old wires and clockwork dials flight deck - not a full-glass. Quite probably the problems caused by digital phones interfering with some aircraft systems simply aren't fully known - hence the ban on phones being switched on in airliners.
I flew a little PA28 with FM-immune King radios the other day - one of the passengers (despite my instruction) had forgotten to switch of his GSM phone and the frequent 'hand shake' pulses could be heard interfering with thee intercomm. Nothing else was affected - but the problem posed by passenger phones shouldn't be underestimated.
Join Date: Jul 2002
Location: UK
Posts: 13
Likes: 0
Received 0 Likes
on
0 Posts
Another issue regarding mobile phones comes not from interference but NETWORK issues.
Mobile phones use frequencies that are line of sight range. That means each mobile cell is about 25-35 miles in diameter (terrain and mast location dependant). Your mobile phone is interrogated by the network (similarly to transponder) about every 10 -15mins, so that the network knows where to direct any calls. If you are higher your phone can "see" more cells and responds to every interrogation, using up network capacity.
The point?
Well, I know a glider pilot who thought it would do no harm to fly with his phone on - it wouldn't affect any of the ac systems. Eventually his network sent him a really nasty letter telling him not to fly with his phone on. They can actually track phones by monitoring which cells the phone responds to - accurate to within 100m apparently.
Now I've distracted you with all this nonsense I'll let you get back to the subject.
Mobile phones use frequencies that are line of sight range. That means each mobile cell is about 25-35 miles in diameter (terrain and mast location dependant). Your mobile phone is interrogated by the network (similarly to transponder) about every 10 -15mins, so that the network knows where to direct any calls. If you are higher your phone can "see" more cells and responds to every interrogation, using up network capacity.
The point?
Well, I know a glider pilot who thought it would do no harm to fly with his phone on - it wouldn't affect any of the ac systems. Eventually his network sent him a really nasty letter telling him not to fly with his phone on. They can actually track phones by monitoring which cells the phone responds to - accurate to within 100m apparently.
Now I've distracted you with all this nonsense I'll let you get back to the subject.
Jet Blast Rat
Join Date: Jan 2001
Location: Sarfend-on-Sea
Age: 51
Posts: 2,081
Likes: 0
Received 0 Likes
on
0 Posts
Yes, 411A - $800 and a small weight penalty on your small aircraft cabin. What about shielding from interference from any cabin position on a 767?
P.S. - how much did your users irritate the phone company? If they were dialling from the air they would be covering several cells, and apparently it is difficult for a cellphone network to cope with large numbers of airborne phones. Also in the UK I believe it is against some phone contracts, as well as being illegal.
P.S. - how much did your users irritate the phone company? If they were dialling from the air they would be covering several cells, and apparently it is difficult for a cellphone network to cope with large numbers of airborne phones. Also in the UK I believe it is against some phone contracts, as well as being illegal.
A few personal experiences
Personal experiences:
(1) A PTT which deflected the engine RPM gauge by 1500 whenever I pressed it.
(2) A set of strobes which I discovered was transmitting on Middle Wallop's tower frequency when I called them up. Turned the strobes off, no problem. Any other frequency, no problem.
(3) A pax who'd left his mobile on, it was contentedly interfering with my intercom making it almost unuseable.
(4) I ran a "building" on a certain Secret-Squirrel airfield which was wired throughout with an aircraft technology (headets) intercom. Resonated frequently with the primary radar ¼ mile away. (Same site had signs at certain spots "no electrically operated explosives past this point", they weren't daft!).
(5) My own mobile routinely interferes with my car cassette player, but never with the radio. It also interferes with the phone on my desk at work if I put it down on that side.
(6) I have two phone (land) lines, recently put in at home. A call on one, can disrupt an internet connection on the other.
(7) A steel control column in a homebuilt which could deflect the compass by 45° with forward stick.
My conclusion - pretty much anything metallic, electrical or electronic can interfere with pretty much anything else. I'm not personally inclined to take chances and would prefer to leave unnecessary kit on the ground or off.
In the day-job I have routinely made myself unpopular by insisting on RF checks on strobes, shielding on pax entertainment systems, etc. So sue me!
G
(1) A PTT which deflected the engine RPM gauge by 1500 whenever I pressed it.
(2) A set of strobes which I discovered was transmitting on Middle Wallop's tower frequency when I called them up. Turned the strobes off, no problem. Any other frequency, no problem.
(3) A pax who'd left his mobile on, it was contentedly interfering with my intercom making it almost unuseable.
(4) I ran a "building" on a certain Secret-Squirrel airfield which was wired throughout with an aircraft technology (headets) intercom. Resonated frequently with the primary radar ¼ mile away. (Same site had signs at certain spots "no electrically operated explosives past this point", they weren't daft!).
(5) My own mobile routinely interferes with my car cassette player, but never with the radio. It also interferes with the phone on my desk at work if I put it down on that side.
(6) I have two phone (land) lines, recently put in at home. A call on one, can disrupt an internet connection on the other.
(7) A steel control column in a homebuilt which could deflect the compass by 45° with forward stick.
My conclusion - pretty much anything metallic, electrical or electronic can interfere with pretty much anything else. I'm not personally inclined to take chances and would prefer to leave unnecessary kit on the ground or off.
In the day-job I have routinely made myself unpopular by insisting on RF checks on strobes, shielding on pax entertainment systems, etc. So sue me!
G
Join Date: Mar 2000
Location: Arizona USA
Posts: 8,571
Likes: 0
Received 0 Likes
on
0 Posts
Send clowns,
They were all dialing in unison from the end of the runway in KLAS at my request to see if any problems occured...and none noted...pleased to report.
This does not mean of course that in the air, problems may develop, so "OFF with 'em" is a good idea, especially in newer glass designs.
Still do believe however that EMF shielding is subordinated in the original design criteria with many aircraft...unfortunately.
They were all dialing in unison from the end of the runway in KLAS at my request to see if any problems occured...and none noted...pleased to report.
This does not mean of course that in the air, problems may develop, so "OFF with 'em" is a good idea, especially in newer glass designs.
Still do believe however that EMF shielding is subordinated in the original design criteria with many aircraft...unfortunately.
Join Date: Dec 2001
Location: England
Posts: 1,389
Likes: 0
Received 0 Likes
on
0 Posts
It's amazing what some people build in their spare time...
http://hot-streamer.com/ross/Biggg/biggg.htm
Scroll down for the best photos, click to enlarge.
http://hot-streamer.com/ross/Biggg/biggg.htm
Scroll down for the best photos, click to enlarge.
Moderator
Interesting thread. May I comment on a few of the posts ?
(a) discounting the overt sensationalism of the New Scientist article, there are numerous more credible and authoritative articles in the literature which show, quite clearly, that there IS a problem. It is not a matter of having to mod the PED ... the even bigger problem is that the basic problem is very rubbery and variable and is related to the range of frequencies and power spectra which some, if not all, PEDs can, and do, radiate and the mass of cables etc which route through the airframe just waiting to have little electrical currents induced in them.
I have one such article scanned from Avionics Magazine if anyone would like a copy by email.
(b) there have been numerous reports over the past 20 or so years since we have seen the introduction of PacMan aircraft where the flight deck instrumentation has done strange things, seemingly inexplicably. Just in one smallish airline in my past, 767s had an uncommanded turn and, on another occasion, screens go black - in the absence of post flight replication, both were presumed to be due to PED interference as far as I am aware.
(c) the suggestion that the problem can be avoided by heavier emphasis on basic instrumentation may or may not be valid depending on where the RF generating PED and the aircraft looms/connectors are relative to one another ....
(d) Do crews always use every bit of information in such a way that an ILS problem will ALWAYS be picked up ? mmmmm ?
Have a look at the Useful URL thread and go to the NZ CAA report on the ANZ Apia incident - longish report but it shows how an experienced and competent crew can get trapped by unusual circumstances.
I have, over the past few years, setup crews working under high load in the simulator for a false capture - not for any reason other than to give those who get caught out something to think about over a beer - and more than a few have been caught by the trap. While some recognise and recover quickly from the situation, others, who are otherwise quite competent, have been totally confused by the unexpected presentation and situation.
It is a facile argument, in the extreme, to dismiss the PED interference problem as being somehow due to pilot incompetence or complacency. To do so is to throw the entire body of CRM and training knowledge out the window .... People can, and do, get into unusual situations where there is a very real potential for hazard.
(e) regarding the question of GPS replacing conventional ground based aids the driving force, unashamedly, is cost. I attended a symposium some years ago where several speakers detailed likely dollar savings - an extremely significant consideration.
(f) to shield all aircraft system looming and connectors adequately would drive up both cost and weight. Certainly an option, but not overly attractive for the Industry.
(g) part of the problem is that the problem is so variable. Given a particular class of PED, this make/model produces a problem, this one doesn't ... and so on .. and the one problem unit may produce a problem in this aircraft, but not that one .....
We have used various ranges of off-the-shelf recording gear (video, tape recorders, etc) for flight test data gathering and never had an observable problem. But that doesn't, for a moment, suggest that one won't crop up in the future.
(h) a solution would be to test all combinations of PED and aircraft ... about 10 seconds' thought will cause that option to be discarded due to cost ....
(i) Kevin's discharge photos are interesting .. but many junior undergraduate physics classes investigate the same shielding phenomena.
I have to agree with Genghis' last post ... who wants to sit for hours in an already uncomfortable aircraft seat wearing head to toe chainmail while the idiot next door plays mad scientists ?
(a) discounting the overt sensationalism of the New Scientist article, there are numerous more credible and authoritative articles in the literature which show, quite clearly, that there IS a problem. It is not a matter of having to mod the PED ... the even bigger problem is that the basic problem is very rubbery and variable and is related to the range of frequencies and power spectra which some, if not all, PEDs can, and do, radiate and the mass of cables etc which route through the airframe just waiting to have little electrical currents induced in them.
I have one such article scanned from Avionics Magazine if anyone would like a copy by email.
(b) there have been numerous reports over the past 20 or so years since we have seen the introduction of PacMan aircraft where the flight deck instrumentation has done strange things, seemingly inexplicably. Just in one smallish airline in my past, 767s had an uncommanded turn and, on another occasion, screens go black - in the absence of post flight replication, both were presumed to be due to PED interference as far as I am aware.
(c) the suggestion that the problem can be avoided by heavier emphasis on basic instrumentation may or may not be valid depending on where the RF generating PED and the aircraft looms/connectors are relative to one another ....
(d) Do crews always use every bit of information in such a way that an ILS problem will ALWAYS be picked up ? mmmmm ?
Have a look at the Useful URL thread and go to the NZ CAA report on the ANZ Apia incident - longish report but it shows how an experienced and competent crew can get trapped by unusual circumstances.
I have, over the past few years, setup crews working under high load in the simulator for a false capture - not for any reason other than to give those who get caught out something to think about over a beer - and more than a few have been caught by the trap. While some recognise and recover quickly from the situation, others, who are otherwise quite competent, have been totally confused by the unexpected presentation and situation.
It is a facile argument, in the extreme, to dismiss the PED interference problem as being somehow due to pilot incompetence or complacency. To do so is to throw the entire body of CRM and training knowledge out the window .... People can, and do, get into unusual situations where there is a very real potential for hazard.
(e) regarding the question of GPS replacing conventional ground based aids the driving force, unashamedly, is cost. I attended a symposium some years ago where several speakers detailed likely dollar savings - an extremely significant consideration.
(f) to shield all aircraft system looming and connectors adequately would drive up both cost and weight. Certainly an option, but not overly attractive for the Industry.
(g) part of the problem is that the problem is so variable. Given a particular class of PED, this make/model produces a problem, this one doesn't ... and so on .. and the one problem unit may produce a problem in this aircraft, but not that one .....
We have used various ranges of off-the-shelf recording gear (video, tape recorders, etc) for flight test data gathering and never had an observable problem. But that doesn't, for a moment, suggest that one won't crop up in the future.
(h) a solution would be to test all combinations of PED and aircraft ... about 10 seconds' thought will cause that option to be discarded due to cost ....
(i) Kevin's discharge photos are interesting .. but many junior undergraduate physics classes investigate the same shielding phenomena.
I have to agree with Genghis' last post ... who wants to sit for hours in an already uncomfortable aircraft seat wearing head to toe chainmail while the idiot next door plays mad scientists ?
Not my field so by all means somebody who understands RF and wiggly-amps much better than me shoot me down, but...
Lets say a new aircraft were designed so that the floor, sides, front and rear of the cabin (including critically the cockpit door) were designed as a Faraday cage, and all the critical electrics and electrics or electronics passed outside that (mostly through the floor) - ceilings can still carry Pax entertainment system electronics, hydraulics, etc. Would this...
(a) Provide a reasonable guarantee of non-interference with systems
(b) Keep the pax happy that they can freely play electronic games, etc.
(c) Block mobile phone signals in any useful direction, thus guaranteeing peace and queit for those not wishing to partake of other peoples conversations, also guaranteeing income for the airline for their overpriced built-in yupee-phone system.
Seems reasonable to me, but then, I'm not an RF engineer.
G
Lets say a new aircraft were designed so that the floor, sides, front and rear of the cabin (including critically the cockpit door) were designed as a Faraday cage, and all the critical electrics and electrics or electronics passed outside that (mostly through the floor) - ceilings can still carry Pax entertainment system electronics, hydraulics, etc. Would this...
(a) Provide a reasonable guarantee of non-interference with systems
(b) Keep the pax happy that they can freely play electronic games, etc.
(c) Block mobile phone signals in any useful direction, thus guaranteeing peace and queit for those not wishing to partake of other peoples conversations, also guaranteeing income for the airline for their overpriced built-in yupee-phone system.
Seems reasonable to me, but then, I'm not an RF engineer.
G
Guest
Posts: n/a
...and would the windows have to be shielded too?
As an avionics maintenance engineer, I have sat in the cockpit of a Classic 747, operating a portable ILS Test Set which transmits low power ILS test signals from an attached wire antenna placed on top of the lightshield. It allows me to produce fly up/down & left/right signals during Autoland tests. I have used this test set in an area where there is little opportunity for test signals to be reflected off buildings and metallic objects. How the signals curve around the nose of the aircraft to the aircraft's receiving antennae on the nose gear/tail is beyond me (or are they reaching the antenna by line of sight.... going through several layers of aluminium to get the antennae?).
What are the odds of a faulty portable device beaming signals out of a cabin window and having those signals bounce off an engine cowl or wing towards an ILS antennae? (producing a subtle fly-down signal on approach on a foggy day). There is no way of preventing these signals reaching the aircraft's external antennae unless the windows are also shielded.
Rgds.
Q.
As an avionics maintenance engineer, I have sat in the cockpit of a Classic 747, operating a portable ILS Test Set which transmits low power ILS test signals from an attached wire antenna placed on top of the lightshield. It allows me to produce fly up/down & left/right signals during Autoland tests. I have used this test set in an area where there is little opportunity for test signals to be reflected off buildings and metallic objects. How the signals curve around the nose of the aircraft to the aircraft's receiving antennae on the nose gear/tail is beyond me (or are they reaching the antenna by line of sight.... going through several layers of aluminium to get the antennae?).
What are the odds of a faulty portable device beaming signals out of a cabin window and having those signals bounce off an engine cowl or wing towards an ILS antennae? (producing a subtle fly-down signal on approach on a foggy day). There is no way of preventing these signals reaching the aircraft's external antennae unless the windows are also shielded.
Rgds.
Q.
Join Date: Apr 2002
Location: North Carolina, USA, Planet Earth
Posts: 75
Likes: 0
Received 0 Likes
on
0 Posts
Genghis,
Unfortunately, a Faraday cage only protects against the electro-magnetic fields and electrostatic fields, but not against magnetic fields. An intuitive explanation of the difference is that close to the radiating device, the separate electrostatic and magnetic fields dominate, while farther away (more than a wavelength or so) they 'combine' to produce what we call radio waves or electromagnetic radiation.
The braided, grounded shield found in most signal cables aboard aircraft protects against EM radiation, and electrostatic fields, but not magnetic fields.
Effective shielding against magnetic fields can be achieved by twisted-pair wiring/differential inputs (generally already implemented) coupled with ferrous (read:iron) shielding which is not generally implemented due to weight and cost reasons.
Unfortunately, a Faraday cage only protects against the electro-magnetic fields and electrostatic fields, but not against magnetic fields. An intuitive explanation of the difference is that close to the radiating device, the separate electrostatic and magnetic fields dominate, while farther away (more than a wavelength or so) they 'combine' to produce what we call radio waves or electromagnetic radiation.
The braided, grounded shield found in most signal cables aboard aircraft protects against EM radiation, and electrostatic fields, but not magnetic fields.
Effective shielding against magnetic fields can be achieved by twisted-pair wiring/differential inputs (generally already implemented) coupled with ferrous (read:iron) shielding which is not generally implemented due to weight and cost reasons.
Join Date: Jul 2002
Location: Darkest Hampshire
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
I'm an RF design engineer, no avionics experience, but I have spent the last 5 years stopping HF radios and now mobile phones from interfering with themselves (insert innuendo here....)
Gengis, the big problem with practical faraday cages is you need to get in and out of them, and their weak spots are always the doors, hatches, lids, etc. You can try and seal them with a conductive gasket, but these tend to be fragile and don't take to repeated opening and closing well. Also as lunkenheimer says, there is no protection against magnetic fields.
QAVION, I don't know anything about how ILS systems work, but I suspect that a portable ILS tester will have a range of around 100 meters. Radio waves decay by an inverse square law, so that when the signal from an ILS tester reaches an aeroplane on approach, the signal will be below the noise floor of it's receiver. Even if it wasn't I suspect that the genuine ILS transmitter would swamp any ILS test transmitters, by several orders of magnitude, and the chances of interference there are minimal.
As to the radio waves propogating round the aeroplane to the ILS receivers under test I suspect that there may be a bit of bending, or fringing. I think it operates at around the same frequency as FM radio, and that isn't particularly line of sight . To be honest I'm getting out of my depth here as I've not touched an antenna design, or anything to do with propogation since university. Once again though the caveat that I know nothing about ILS, so if I have missed something fundamental please let me know.
EM interference is a strange unpredictable business, and you cannot easily predict how things will interact with each other. In other words, switch it off. And it's a top excuse to not do any work while travelling!
Cheers
John
Gengis, the big problem with practical faraday cages is you need to get in and out of them, and their weak spots are always the doors, hatches, lids, etc. You can try and seal them with a conductive gasket, but these tend to be fragile and don't take to repeated opening and closing well. Also as lunkenheimer says, there is no protection against magnetic fields.
QAVION, I don't know anything about how ILS systems work, but I suspect that a portable ILS tester will have a range of around 100 meters. Radio waves decay by an inverse square law, so that when the signal from an ILS tester reaches an aeroplane on approach, the signal will be below the noise floor of it's receiver. Even if it wasn't I suspect that the genuine ILS transmitter would swamp any ILS test transmitters, by several orders of magnitude, and the chances of interference there are minimal.
As to the radio waves propogating round the aeroplane to the ILS receivers under test I suspect that there may be a bit of bending, or fringing. I think it operates at around the same frequency as FM radio, and that isn't particularly line of sight . To be honest I'm getting out of my depth here as I've not touched an antenna design, or anything to do with propogation since university. Once again though the caveat that I know nothing about ILS, so if I have missed something fundamental please let me know.
EM interference is a strange unpredictable business, and you cannot easily predict how things will interact with each other. In other words, switch it off. And it's a top excuse to not do any work while travelling!
Cheers
John
Join Date: Nov 2000
Location: Melbourne,Vic,Australia
Posts: 423
Likes: 0
Received 2 Likes
on
2 Posts
Qavion
We observed this effect some years ago experimenting with 173 and 433Mhz in and around metal buildings. These had a door and windows on one side only. When the transmitter was inside and the signal strength was measured on the outside of the opposite side it was quite strong close (~ one wavelength) weakened as the distance increased and then increased (presumably due to reflections from distant buildings). This was thought to be either:
The signal going out the door/windows and around the outside as a ground (wall?) type of propagation or
The building acting as a faraday cage/antenna
The one conclusion we reached in the playing around was that the higher frequency gave better results at the same power levels presumably as the shorter wavelength went through doors and windows better. Any other conclusions were obscured by the fact that it was extremely difficult to get any form of reproducable results - then we started testing with a body lying on the transmitter.
We observed this effect some years ago experimenting with 173 and 433Mhz in and around metal buildings. These had a door and windows on one side only. When the transmitter was inside and the signal strength was measured on the outside of the opposite side it was quite strong close (~ one wavelength) weakened as the distance increased and then increased (presumably due to reflections from distant buildings). This was thought to be either:
The signal going out the door/windows and around the outside as a ground (wall?) type of propagation or
The building acting as a faraday cage/antenna
The one conclusion we reached in the playing around was that the higher frequency gave better results at the same power levels presumably as the shorter wavelength went through doors and windows better. Any other conclusions were obscured by the fact that it was extremely difficult to get any form of reproducable results - then we started testing with a body lying on the transmitter.
