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airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Using GPS Onboard Aircraft?

Wed Dec 08, 2004 7:35 am

Without any PED on an a/c there is already more than enough to be concerned of in terms of EMI and RFI.

That is a dangerous assumption that should not be decided by the average passenger.

Aircraft systems self-generated EM and RF interferences are higher than any (unintentionally radiating) PED's interference.
Am I wrong ?


Simply put, yes you are wrong. All aircraft systems generate electrical fields. If they interfere with other aircraft systems, they simply don't get approved. Be it light fixtures or complex navigation systems. Some have nastier failure modes than others but for the most part they are put through rigorous testing to establish their potential for interference.

The spectrum on aircraft is tightly controlled and components are designed to prevent interference. The fact that you have an aircraft transmitter capable of transmitting 50 watts through its antenna in the VHF band doesn't mean it has more potential to interfere with avionics than your handheld GPS that has a tiny interference signature.

It all depends on the spectrum it emits and the proximity of the device, and 6 other factors identified over and over in this discussion.

The manufacturers of avionics components are well aware of the other devices typically found on board and design accordingly. PEDs are a mystery. There is no standard for PEDs so nothing specific to design around.

The issue here is not my overreaction. I have stated a few times that the risk of PEDs affecting aircraft systems is low. Unfortunately the results may be catastrophic. The real issue here is the proliferation of misinformation regarding the potential for interference.

Iakobos, why not scold the person who wrote:

That's just sheer lunacy. The electronic emissions thing is garbage, especially with a receive-only device like a GPS receiver.

With all the information presented on the subject here, wouldn’t you agree that this person is overreacting? Or at least presenting a misinformed opinion?
 
iakobos
Posts: 3255
Joined: Wed Aug 06, 2003 6:22 pm

RE: Using GPS Onboard Aircraft?

Wed Dec 08, 2004 8:47 am

Absolutely, I concur that N328KF's statement is completely over the top.

Non-controversial sidenote: I would be very interested (from a technical point of view) to see the graph of a spectrum analyzer inside an airliner (without passengers...), especially during the flight's critical phases.
 
Newark777
Posts: 8283
Joined: Thu Dec 02, 2004 6:23 am

RE: Using GPS Onboard Aircraft?

Fri Dec 10, 2004 9:23 am

http://money.cnn.com/2004/12/09/technology/personaltech/cellphones_inflight/index.htm?cnn=yes

If cell phones are so dangerous during flight, why would anyone even consider allowing their use during flight? I'm not taking any side in the matter, I would just like your professional opinion, since you guys seem to have a lot of experience in the field.
Why grab a Heine when you can grab a Busch?
 
iakobos
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Joined: Wed Aug 06, 2003 6:22 pm

RE: Using GPS Onboard Aircraft?

Fri Dec 10, 2004 9:18 pm

Newark,

The article does not say that cell-phones "are so dangerous" and indeed they are not intrinsically "dangerous" (as in DANGER !) but one thing is certain, since they are meant to radiate electromagnetic energy they constitute one more element to take care of in terms of electro magnetic interference, in an environment which is already packed with a web of wires and devices.

As far as I know, there has never been one single clear cut case where a cellphone has been proven to bear the guilt for harmful interference.
But, and here I join Airplay, the risk is not and will never be zero.

It should be understood also that interference implies two components,
the supposedly interfering and the supposedly interferred, and that the interfering element is not necessarily the culprit.
Put a cellphone next to a computer display and you will see that interference exists, though (from a tecnical point of view) the display is "at fault", not the cellphone. Might seem strange to most, but so it is.

Standards and regulations are made to foresee as much as possible the eventuality of conflict, though they cannot encompass all possible cases.

As to the future of wireless cells being installed and personal cellphones used onboard a/c, we must recognize
- that there is a (big) demand
- that there is an underlying strong marketing point for airlines
- that it is a welcome revenue generating system for airlines, installation and maintenance companies, the various service providers (cell + satellite) and various network operators (cell + satellite + fixed land).

For me, the question is not if but when and how.

ps: I am personally a proponent of a "data only" service.

 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Using GPS Onboard Aircraft?

Sat Dec 11, 2004 6:01 am

I have witnessed a cell phone cause oscillation in FD/Autopilot, cause a cabin systems control computer reboot, and cause an autopilot to disconnect.

Overall its a bad idea to have unregulated transmitting devices on board aircraft. This could change by raising the design standards even further but I doubt the airlines want millions of dollars added to the price of aircraft just allow cell phone use.
 
bcbhokie
Posts: 196
Joined: Fri Sep 24, 2004 7:30 am

RE: Using GPS Onboard Aircraft?

Sat Dec 11, 2004 1:07 pm

Airplay:

you piqued my curiosity with this statement:

"I have witnessed a cell phone cause oscillation in FD/Autopilot, cause a cabin systems control computer reboot, and cause an autopilot to disconnect."

Was this in an actual aircraft in flight, actual aircraft on the ground, or in a lab? if the latter (in a lab), how far away from the avionics equipment was the transmitting radio and antenna? Also, where does the autopilot control equipment usually live in an aircraft?

I'm curious because, as you know, this directly affects the probability of the problem cropping up in the real world.

Thanks,
Ben
 
Newark777
Posts: 8283
Joined: Thu Dec 02, 2004 6:23 am

RE: Using GPS Onboard Aircraft?

Sat Dec 11, 2004 2:10 pm

Thanks for the explanation Iakobos. Kind of scary, though, that the government would allow use of a phone if it has the possibility to take the plane down.  Sad
Why grab a Heine when you can grab a Busch?
 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Using GPS Onboard Aircraft?

Tue Dec 14, 2004 3:17 am

Bcbhokie,

All instances were during certification testing. And they were all caused by unauthorized use of the cell phone during testing.

The instance of the FD/Autopilot oscillation happened while we were doing in-seat power supply testing. The flight crew were under instructions to report anomalous behaviour while we were testing in the cabin. We were at low levels throughout the flight since we wanted to perform the tests at the most critical phase, approach and landing.

Long story short, the maintainance guy assigned to the airplane was sitting in the first row of seats talking to his girlfiend on his cell phone. We were able to positively associate the interference to the cell phone by turning it on and off.

In this particular airplane, the 737, most of the avionics "live" in the avbay in the underbelly area of the forward fuselage area. Proximity to the avbay isn't the only factor however. Remember that there are windows and lots of metal out there to reflect signals to the antennas.
 
iakobos
Posts: 3255
Joined: Wed Aug 06, 2003 6:22 pm

RE: Using GPS Onboard Aircraft?

Tue Dec 14, 2004 6:07 am

Airplay,

I assume the fuselage and the "groundfloor" were not made of thin plastic material and the avbay equipment was not left unshielded and un-racked.

Let's be serious, the 2W of radiated RF, at a distance of 3.5m and in free space, represent a field intensity of 0.0162 Watt/square meter, which corresponds to an electric field of 2.46V.
This is at 3.5 meters, in the best direction and elevation for the cellphone antenna and assuming there are no obstacles between the antenna and the "unfortunate receiver".

As you say yourself, RF waves at 800 or 900MHz bounce back very well from hard surfaces, not only metallic ones. In other words, any particular hard surface is a shield, and on these frequencies a good shield.

I can go much deeper in details, but clearly this cannot be a case of (direct) RF interference.

Though I do not dispute the "we could positively associate the interference to the cellphone", but then tell me, did you locate the (faulty or unshielded) element which served to conduct the interference, and why was the FD equipment susceptible to the interference when it should not have been ?
 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Using GPS Onboard Aircraft?

Tue Dec 14, 2004 7:25 am

Iakobos, your discussion style is becoming tiresome. Do we really need to go over all this again?

I assume the fuselage and the "groundfloor" were not made of thin plastic material and the avbay equipment was not left unshielded and un-racked.

Believe it or not, there are several apertures that make it possible to pass RFI from compartment to compartment in aircraft. Furthermore, wiring leading to the avbay under the floor makes its way above the floor to antennas and other equipment in the cockpit and cabin. There are also the apertures supplied by the plastic IFE disconnects in the floor. And…..there are a GREAT deal of aircraft that use composite non-metal floor panels. Many use 2 thin kevlar or fibreglass layers with a cardboard (nomex) honeycomb core. Go figure….

Let's be serious, the 2W of radiated RF, at a distance of 3.5m and in free space, represent a field intensity of 0.0162 Watt/square meter, which corresponds to an electric field of 2.46V.
This is at 3.5 meters, in the best direction and elevation for the cellphone antenna and assuming there are no obstacles between the antenna and the "unfortunate receiver".


If you are saying that 2 Watts of radiated RF can not possibly interfere with onboard equipment, then you sir are quite misinformed. Period. A 2 Watt signal can be easily received 50 miles away or more. If a cell phone can't transmit a field that is usefull 3.5 metres away, how do you expect it to communicate with a cell tower miles away?

As you say yourself, RF waves at 800 or 900MHz bounce back very well from hard surfaces, not only metallic ones. In other words, any particular hard surface is a shield, and on these frequencies a good shield.

When did I say that? Besides, when you consider digital transmissions, you must also consider the lower band emissions they emulate. Ask any CL-415 pilot about the DME. The DME antenna sits just aft of the cockpit hatch. You can actually hear ticking from DME transmissions through your headset…even if its not plugged in. DMEs operate at about 1.2 GHz but they manage to induce enough interference through metal skin and into your audio headset to hear the transmissions.

I can go much deeper in details, but clearly this cannot be a case of (direct) RF interference.

Yes…you might as well stop there since your analysis is irrelevent. It is quite a subjective statement that comes down to your word against mine.

Though I do not dispute the "we could positively associate the interference to the cellphone", but then tell me, did you locate the (faulty or unshielded) element which served to conduct the interference, and why was the FD equipment susceptible to the interference when it should not have been ?

Ah…finally a valid question. The aircraft was a 200 series 737. This vintage equipment is not HIRF hardened. It was never designed to operate with unintentional or intentional portable radiators on board. Older aircraft are actually more susceptible to EMI/RFI. Now maybe you can answer me this…when you put your cell phone next to your computer and you observe interference, is it because the computer is operating at 900MHz? Why is there a buzz in the speakers? Why does your monitor act strange? Remember my statement about lower band emissions that digital cell phones emulate?

When we install transponders or DMEs its common practice to install L-Band filters on ADF antennas. Any idea why? Probably not….

I’ve said as much as I need to on this subject. I really have no desire to enter this endless loop of a discussion and re-hash the same information over and over Iakobos. Your statements about the potential effects of PEDs on aircraft are obviously mis-informed and dangerous.

I obviously can’t stop you from speaking your mind in a public forum, but I think I’ve presented a great deal of information and personal experience to support my statements…to no avail. So go on and operate your PEDs at the risk of the safety of your fellow passengers. I will continue to remind the violators of the regulations and report them to flight crew when required. Unfortunately far too many arm-chair engineers feel they know better…..
 
timz
Posts: 6581
Joined: Fri Sep 17, 1999 7:43 am

RE: Altitude

Tue Dec 14, 2004 8:14 am

"Airliners don't fly at 38,000 feet.... up to now."

You mean they don't level off at that altitude (in the US). So maybe he was descending?

Standard-day pressure drops by around 5% per 1000 feet at that altitude-- so I guess 38000 ft couldn't equal FL370? (But GPS altitude of 38000 ft would be around 37900 above sea level...)
 
iakobos
Posts: 3255
Joined: Wed Aug 06, 2003 6:22 pm

RE: Using GPS Onboard Aircraft?

Tue Dec 14, 2004 11:05 am

Airplay,

In my eyes what could become tiresome in the long run is constantly raising the red flag without feeding us a single element that would corroborate your "I have seen it and it's enough" attitude.

If you are saying that 2 Watts of radiated RF can not possibly interfere with onboard equipment, then you sir are quite misinformed. Period. A 2 Watt signal can be easily received 50 miles away or more. If a cell phone can't transmit a field that is usefull 3.5 metres away, how do you expect it to communicate with a cell tower miles away?

For you information, 2Watt of RF signal at 800MHz can be perfectly received at several hundred kilometers, provided there is an adequate antenna and adequate receiver at the other end.
But what will arrive over there is an electric field of the order of tenths of a microVolt, that is 7 digit after the dot.
What you need to produce (off band) RF interference is a few millions time that much.

Now maybe you can answer me this…when you put your cell phone next to your computer and you observe interference, is it because the computer is operating at 900MHz? Why is there a buzz in the speakers? Why does your monitor act strange? Remember my statement about lower band emissions that digital cell phones emulate?

When I put a cellphone next to a PC nothing happens, sorry.

When I put it next to a display with a cathode ray tube, the latter flickers, right. But I suppose you know why. If not, I'll tell you that a display is by its own nature an open case, not a shielded device. The electric field produced by your cellphone at a very short distance is enough to alter the field created by the deflection coils around the CRTube. That's all there is, and the weak link in this is not the cellphone but the display. (ps no problem with TFT since they have no deflection coils)

Buzz in the speakers, sure, you know why ? same thing, the speaker magnetic fied is disturbed. Put alu paper around your speaker, or move further away by half a meter, problem solved.

DME clicks in headsets ? disturbance of the speaker magnets. Put a sheet of paper on top of your head and tell me what happens.

Lower band emissions ? here you are on your own and you show you are not at ease with RF circuits. Any device made to radiate energy does so at the intended frequency (aka f0), but some spurious (unintended) radiation will also appear on higher frequencies, not lower. These unwanted signals are the by product of non-linearity in amplifying circuits, resulting in largely attenuated but still present signals on frequencies called "harmonics" and corresponding to 2 x f0, 3 x f0, etc...

I obviously can’t stop you from speaking your mind in a public forum, but I think I’ve presented a great deal of information and personal experience to support my statements…to no avail.

You have presented nothing at all. You only mentioned that you saw things.
To come back to your last example, I reiterate my question, did you identify the faulty component ?
Because there was something wrong. The FD/AP system is no intrinsic receiver and clearly is inside a chassis and shielded/grounded and so are the various cables and harnesses. Any interference susceptible to alter the functions of the unit have to be brought inside directly along a wire, not by mere radiation of a 2V electric field. Nonsense.

In all honesty, tell me that a cellphone put next to the FD/AP unit (correctly installed and grounded), does interfere.
If it was so, there is not a single aviation authority in the world that would allow pax carrying cellphones onboard, even switched off.
 
KDTWflyer
Posts: 825
Joined: Tue Jun 29, 2004 12:51 pm

RE: Using GPS Onboard Aircraft?

Tue Dec 14, 2004 1:00 pm

Below is a picture of the GPS I've used on many flights. It works very well and is a nice asset to have on IFE-less flights.

 
mandala499
Posts: 6600
Joined: Wed Aug 29, 2001 8:47 pm

RE: Using GPS Onboard Aircraft?

Tue Dec 14, 2004 1:10 pm

One thing I would like to know from Airplay is...
What was the system of the phone what was used to test that -200 that caused an FD oscillation?

Analogue? CDMA? GSM? PCN?

someone once told me the wave transmission pattern of these different systems can affect different types of equipment.

Mandala499
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Using GPS Onboard Aircraft?

Wed Dec 15, 2004 1:09 pm

*Yawn*....

In my eyes what could become tiresome in the long run is constantly raising the red flag without feeding us a single element that would corroborate your "I have seen it and it's enough" attitude.

May I suggest a course in reading comprehension sir.

When I put a cellphone next to a PC nothing happens, sorry.

Then you and your PC have not satisfied the criteria identified by the guidance material. Remember the 8 items? Does this mean that there is no chance in a billion that it MAY cause interference?

Buzz in the speakers, sure, you know why ? same thing, the speaker magnetic fied is disturbed. Put alu paper around your speaker, or move further away by half a meter, problem solved.

Try it around the wires leading to the speakers. This may get you thinking...

DME clicks in headsets ? disturbance of the speaker magnets. Put a sheet of paper on top of your head and tell me what happens.

Again. Reading comprehension can do wonders. The DME in question is behind metal skin. What exactly will the paper do? Perhaps you can try the paper...but roll it up in a cone first.

Lower band emissions ? here you are on your own and you show you are not at ease with RF circuits. Any device made to radiate energy does so at the intended frequency (aka f0), but some spurious (unintended) radiation will also appear on higher frequencies, not lower. These unwanted signals are the by product of non-linearity in amplifying circuits, resulting in largely attenuated but still present signals on frequencies called "harmonics" and corresponding to 2 x f0, 3 x f0, etc...

I specifically and intentional avoided using the term "harmonics". When you have high power high frequency emmissions being transmitted in class C, there is potential for interfernce at low frequencies. Not because of the harmonics of the carrier, but because of the frequency of the modulating pulses (PRF) and the relatively high power. You can hear the ticking of the bursts of the modulated pulses from the DME antenna.

In a broad sense, an RF is made up from the fundamental frequencies and harmonics which are products of modulation. Most radio signals have the majority of their significant harmonics near the carrier frequency. Transponders, DME, and Weather Radars are unique in that they have carriers in the GHz range but class C modulation at a rate of less than 1Khz. This results in a strange ability to emit EMI from an RF source that is in the audio band.

You have presented nothing at all. You only mentioned that you saw things. To come back to your last example, I reiterate my question, did you identify the faulty component ?

What faulty component? The airplane was not designed to operate with cell phones in use in the cabin and therefore cell phone use is restricted. The anomaly was due to operation outside the normal opeating parameters. Would I forward the results to the FAA if we couldn't get the airplane pressurized with the door open?

Because there was something wrong. The FD/AP system is no intrinsic receiver and clearly is inside a chassis and shielded/grounded and so are the various cables and harnesses. Any interference susceptible to alter the functions of the unit have to be brought inside directly along a wire, not by mere radiation of a 2V electric field. Nonsense.

Yep, nonsense. Boeing, Airbus, the RTCA, ARINC, the FAA, TCCA, EASA....all a bunch of clowns. Those reports of cell phone interference must have been a mistake...no a conspiracy. Why can't well all see the light Iakobos? Why are you the only one immune to the nonsense?

In all honesty, tell me that a cellphone put next to the FD/AP unit (correctly installed and grounded), does interfere. If it was so, there is not a single aviation authority in the world that would allow pax carrying cellphones onboard, even switched off.

Yes it can, it has, and it does. I find it strange that this conversation started with a GPS receiver and morphed into a cell phone discussion. Intentional radiators like cell phones are currenlty prohibited from use on board airplanes. There are a few exceptions lately with the advent of TPEDSs guidance. I got the RTCA TPED standards recently. The 302 pages tell me its not going to be easy to certify TPEDs. And the limit for emmisions as far as I can tell so far is 20dBm.

How many more times will ask why cell phones are not banned Iakobos? They are. Why do they not ban them outright (off or on)? Because the prohibition is viewed as an appropriate measure based on the probability of interference which has been established as being low.

So far the low probability along with the dilegence of flight crew and the skill of designers has minimised the impact of irresponsible passengers. I wonder how long the luck will hold...
 
iakobos
Posts: 3255
Joined: Wed Aug 06, 2003 6:22 pm

RE: Using GPS Onboard Aircraft?

Thu Dec 16, 2004 12:17 am

May I suggest a course in reading comprehension sir
Unless one of your posts was deleted or does not appear on my (impartial) display, I cannot see one occasion where you showed the problem + the source + the path.

20dBm in the near future eh ?
100mW...the lower power level of cellphones. Interesting.
AirCell’s system that would allow you to use your cellphone is quite controversial and I doubt you’ll be seeing it any time soon. Especially on airliners.
Perhaps we should leave it at that and cross lines again in a year or two.

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