Could a handheld GPS interfere with the INS system?

[Contacttower]

Someone on the SLF forum asked about GPS use during an airline flight...and I was wondering:

Could a GPS system like a Garmin 496 (or similar) interfere with any of the equipment in the cockpit? I would have thought that since they are usually used in aircraft anyway there wouldn't be a problem.

I take it airliners still use GPS updated INS rather than just straight GPS?

[Doors To Manuel]

I hope the answer is 'no' ! I use my Garmin on most flights and it is very rare to find explicit advice in the inflight mag or elsewhere on whether or not it is prohibited. They all go on about mobile phones and now also anything with earphones, but rarely mention GPS.
On a recent BA flight the announcement was to 'check in the Highlife Mag for more details' ...but there were none.
So until I hear otherwise I will still be the pillock who taps on the cockpit door and whispers, "psst, turn left at Belgium, mate".

[Check Airman]

As a rule, devices that transmit or receive data on the electromagnetic spectrum may cause interference. Portable radio, TV, Bluetooth, Wi-Fi, and GPS are all potential sources of interference. The other day I was flying and the DME readings were all over the place. I remembered that my cell phone was left on. I turned it off and the DME eventually settled down. Please, unless you're flying a glider or light sport aircraft, keep your GPS off. If you really want to know your speed, ask before or after the flight. The crew will gladly entertain such questions.

[Contacttower]

unless you're flying a glider or light sport aircraft, keep your GPS off.


That goes against the practice of the vast majority of GA in this country. GPS is used (even in the handheld type) a lot in Group A aircraft alongside all the other VOR/ILS/DME/ADF stuff in the cockpit. Mobile phones interfering with the DME is a completely different issue though.

I asked the question not because I want to use GPS during a commercial flight but because if it has the potential to interfere with airliner systems it has the potential to interfere with the avionics in my plane as well...which is very worrying.

[SpamCanDriver]

Im probably wrong but I was under the impression the a GPS unit only received the signal from the satelite and did not transmit anything! And as such the only risk of interference would be from the electromagnetic field generated by electronics. i.e. very small

[Spooky 2]

Small point of order here but GPS nor any ground based nav aids actually update INS. The INS, IRS ADIRU etc. only interface with the respective FMS and do not receive any updates directly from any ouside sources. If your really brave you can do an INS update by flying over a navaid and do a manual update, but that's not the same as you had implied. For all of you who that anyway, forgive me for being redundant.:ok:

[Contacttower]

Small point of order here but GPS nor any ground based nav aids actually update INS. The INS, IRS ADIRU etc. only interface with the respective FMS and do not receive any updates directly from any ouside sources. If your really brave you can do an INS update by flying over a navaid and do a manual update, but that's not the same as you had implied. For all of you who that anyway, forgive me for being redundant.:ok:


Thanks for clearing that up- sorry I don't know a huge amount about INS systems...although I had heard the phrase 'GPS updated' before and assumed that that was what it meant. I just tacked on the question about INS because I was curious.

[FE Hoppy]

While your GPS is not an active transmitter it is classified as a passive transmitter. I read some guidance from one manufacturer that said they should not be allowed. Basically anything with an antenna is a risk. Of course how much of a risk is questionable but if it hasn't been specifically approved then you are adding risk by using it.

[Dan Winterland]

Quote Spooky: "Small point of order here but GPS nor any ground based nav aids actually update INS. The INS, IRS ADIRU etc. only interface with the respective FMS and do not receive any updates directly from any ouside sources."

Depends on the system. On the three large aircraft types I have flown which had GPS updating, the IRSs all used very different methods of updating position. My current type uses the FMC to produce a blended position which is weighted depending on the quality of the information fro a Multi Mode Receiver which has an inbuilt GPS along with a VOR, DME and ILS. The FMC tells you on the progress page which position it is using, it's nearly always 'GPS Primary'. The type before that used an IRS position which was updated by GPS and the type before that had an IRS with a GPS embedded in it, so the IRS position itself was a blended position.

From my experience, I would doubt a GPS set would disrupt the aircraft electronics at any stage of the flight. But of course you should pay regard to the current airline policy. Mine tells the passengers, 'No electronic items are to be used until the seat belt signs are turned off after take off - and they must be turned off again when the seat belt signs are back on for landing".

But also, I haven't found a GPS set which works in a cabin. Not that I've tried very often!

[parabellum]

Surely the following post by radeng in the Pax & SLF Forum answers the question: (Including you, Doors to Manual ;))

radeng (http://www.pprune.org/forums/member.php?u=32414)
Over 250 posts so far. Perhaps I should click here (http://www.pprune.org/ptorder/ptorder.htm) and order a Personal Title

Join Date: May 2001
Posts: 414


If the GPS receiver is a direct conversion type, then the biggest possible cause of interference is to the on board GPS. Not desirable. But if it's a superhet, then we have a potential problem. If it meets FCC (US) requirements on oscillator radiation, it could well have an Intermediate Frequency such that the local oscillator blocks a DME channel. If it meets EU standards, possibly not - but only possibly, depending upon which stanadrds the manufacturer has decided to declare it compliant to.
As far as cell phones are concerned, any LO radiation if the receiver uses high side injection could kill a DME channel. A complication arises in that the immunity of cabling on a nice new aircraft is quite likely to be different to that on a 10 or 20 year old aircraft where corrosion, movement etc have happened.
The problem is that as far as aircraft systems are concerned, you KNOW what frequencies are involved. Bringing in unknowns (because you DON'T know the frequency plan of every possible bit of equipment) is another matter. Add to that the fact that there isn't just the fundamental radiation to worry about, but the presence of intermodulation products when authorised transmissions are made from the aircraft, there is a VERY good reason for banning the use of these things.
If you wonder about my qualifications, 'radeng' is a reduction of 'radio engineer'.

[Paradism]

Contacttower
"I would have thought that since they are usually used in aircraft anyway there wouldn't be a problem."
To be blunt, but I hope not unkind, what you think is not relevant. Aviation legislation prohibits the use of any electronic/electrical equipment on aircraft for which that aircraft is not approved. The approval may be a general one, as in mobile phones, or may be more specific.

On a technical note, there are many aircraft systems that are susceptible to interference from electromagnetic interference "EMC", FADECs are a particular case. In the modern world, most electronic devices are digital such as laptops, GPS, mobiles, calculators, etc., and clearly an aircraft and its systems cannot be tested for interference from all specific devices.

You can imagine the case where "Doors to Manuel" is sat in the back of a nice modern twin donk and decides to switch on his GPS. Immediate effect, both FADECs cough and splutter and the wicks go out. As far as I can see, the only good thing that will come out of the scenario is that he will know precisely where the crash is.

Bottom line, any equipment to be used on an aircraft must have been tested and proven not to interfere with aircraft and its systems. That is an expensive business but cheaper than finding out the hard way.

[jezzbaldwin]

Off at a tangent here, but I once had a girlfriend who had a cochlear implant (effectively bionic hearing). A magnet and electrodes are implanted within the head - the purpose of the electrodes are to stimulate the cochlear thus allowing the deaf to hear (supposing the auditory nerve is OK), and the magnet is there to hold a transmitter firmly in situ outside the skull.

The advice given by the cochlear implant centres is that this device should be turned off for TO and landing however when asked, neither Boeing or Airbus provided a conclusive answer. To me this seemed to be a problem as here was a SLF who needed to be transmitting in order to hear the safety briefing.

So

Not quite the same, but we did about 2.5 hours of testing with her in a Cherokee - try as we might, it was impossible to get her to interefere (well, interefere with the avionics - she was a natural pilot when interefering with the controls, and incidentally the deaf who have hearing corrected with a cochlear implant are NOT precluded from a class 2 medical).

The next step was on an A320. I was also SLF on this occasion, and pre departure talked through my tests with the P1. The result was that he was happy to contine our test on this flight. We put her "down the back", as far away from the e-bay as possible. All was fine.

Its just a thought should anyone encounter a cochlear implant PAX in the future.

And one other point - I have no idea what frequency range these contraptions work within, but the various cochlear implant centres are always willing to field intelligent questions.

[martinidoc]

The thing that worries me is that if there is a real possibility of mobile phones interfering with critical A/C systems, then I do not believe that the present procedures, which simply involve an announcement that all mobiles should be switched off whilst engines running to be sufficiently robust. I regularly travel as SLF on Airbuses, and it is a regular occurrence for PAX to remember to switch off phones during flight, or for phones to go off. This probably represents the tip of the iceberg. I have to confess that on one occassion I have also found after the flight that I had inadvertently forgotten to turn my mobile off. So even where there is no intention to deliberately keep one's mobile on, there will be a significant failure rate in compliance.
From my own experience on smaller A/C, I usually keep my mobile on as the last line of defence backup for Radio failure. (Being over cautious on all trips other than local instructing details I also have a hand held battery operated transceiver and GPS - Call me paranoid!). I only turn the mobile off if I'm doing a "critical" instrument approach in IMC conditions. The only interference that I have experienced is the pip pip in the headset, presumably the Mobile interacting to find the relevant cell transmitter. I accept however that an A/C like the PA31 has much less critical electronic dependancy than an Airbus which is completely fly by wire.
Perhaps cabin crew should check all mobile phones when they check the boarding passes? The difficulty with this would undoubtedly be delays to boarding, and arguments with owners of "multifunctional" devices which have a flight safe mode.
One further thought, it has been announced that certain carriers will be running services which are enabled to handle mobile phones in flight. How is this consistent with the previously stated interferences to DME/FADEC? Will there be better electronic isolation of the A/C systems to facilitate this?

[OzExpat]

I suspect that the really simple answer is that nobody wants to find out for sure because it MIGHT end the airline monopoly on telephone call charges. I think that, if anyone had ever wanted to run a properly constructed scientific trial on any PED (Portable Electronic Device), the first problem they'd encounter outside of the airline itself, is the myriad frequencies and potential interactions between the various types of PED.

Now, as one who designs instrument procedures, I know that the tolerances can (on occasion :eek: ) be right on the limit. Think about that for your next take-off and landing - then ask yourself... do I really want to jeopardise any of those OCCASIONALLY tight tolerances?

On a personal note, I don't think that anyone really knows the answer to this so it's undoubtedly safer to err on the side of caution. I'm not yet convinced, one way or the other on the issue of PEDs, but I sure don't want to find out the HARD way.

[Spooky 2]

I have to call you on that one. There is no IRS/IRU/ADIRU that updates from any external source...in any civil aircraft, be it Honeywell, Litton, etc. The FMC (FMS) will up date from GPS/DME/LOC/VOR.

Can you expand on your aircraft type and specific model? I suspect it is either a 777 or 747 as both of these use the MMR. The question as I understood it was, can the IRS/IRU/ADIRS be updated by the GPS. To my knowledge the answer is No. The blended positions from the FMC (FMS) are not a result of any IRU, GPS updating, but rather a blened position as a result of all the information gathered. On the 777 you can see these individual values on the POS REF page along with the MAP Display.

[Contacttower]

To be blunt, but I hope not unkind, what you think is not relevant. Aviation legislation prohibits the use of any electronic/electrical equipment on aircraft for which that aircraft is not approved. The approval may be a general one, as in mobile phones, or may be more specific.



A Garmin GPS has been approved for use in aircraft...it has been tested by the FAA...and it says so in the instructions. OK what I think isn't really relevant but if a GPS can mess with stuff in an airliner it can mess with stuff in my all-singing, all dancing airways certified spamcan (not that I own one) which is worrying.

[Gadget freak]

Spooky,

Not sure that all civil aircraft do the GPS / inertial integration in the FMS. Check out the Nothrop Grumman LTN-101E, both in terms of what it does and what aircraft it's on.

[Spooky 2]

Well after looking up as much as possible regarding the LTN-101E I can only see reference to "sole means of navigation with GPS accuracy". Typical double speak so just what is happening here that is unique to this design has escaped me? I suspect that the GPS is an integral part of the IRU technology and unlike the Honeywell product line which typically uses a data port, the Litton system has it integrated into the IRS???

Thanks for the reference!

[Pugilistic Animus]

interesting discussion


JezzBaldwin:---hearing aids/ and pace makers are excepted form the PED ban under the FARs

[None]

Here is one airline's web site remarks concerning GPS.


You can use these while the plane is at the gate with the doors open, after the plane has taken off and reached its cruising altitude and before it begins to descend for landing, and after the plane has landed and is taxiing to the gate.

Personal digital assistants
Personal computer games
GPS (global positioning satellite) systems

Your flight attendant will announce when it is safe to use these devices.

[Check Airman]

When people note that some aircraft (even light aircraft) already have GPS, remember that these are not bought at Radio Shack and pasted onto the panel. They are integrated into the aircraft systems, and so proper precautions are taken at the design stage, so they do not affect each other.

Now I don't know, but MAYBE Garmin has engineered their handheld aviation units so that they don't affect plane systems. That's the only way I can imagine you could safely use it in a Cessna. In this case, the equipment would have met the relevant certification standards. This is unlike waking into a store and picking a unit off the shelf and using it in a plane.

[Contacttower]

This is unlike waking into a store and picking a unit off the shelf and using it in a plane.


Of course...I should have stated in my question that I am talking about GPS systems as sold in pilot shops from reputable aviation accessories manufacturers like Garmin or Bendix...I wasn't talking about 'any old GPS' if you see what I mean.

The GPS systems I am referring to are ones designed and certified for use in aircraft.

[SNS3Guppy]

Small point of order here but GPS nor any ground based nav aids actually update INS.


Our three onboard INS units all receive GPS updating, and it's not a small point. We're limited in class II nav to certain time constraints without that GPS updating.

[twistedenginestarter]

GPS signals are extremely weak - less than the ambient noise level. It is indeed a wondrous feat that your GPS chip can pick up the signal at all, let alone guide you round the skies. My guess therefore is the GPS electronics would be very low noise generators, otherwise the GPS wouldn't be able to work. I understand there are different frequencies involved and that the GPS has to generate frequencies to beat, but noise is noise and you imagine a GPS must be the quietest thing that isn't a mouse.

[twistedenginestarter]

This INS thing is a bit of a red herring. ContactTower seemed to be saying his GPS might upset things. Perhaps another GPS might be the most prone. That GPS might show some misreading which could corrupt the FMS's opinion of where it was. That sequence of events is unlikely. GPS is digital so you can't 'bend' the reading, and wherever navigation information is blended there is going to be some process which rejects 'odd' inputs. The loss of a valid GPS input is something that would be designed for.

[Dream Land]

The title of this thread asks about interference to INS, I thought INS was a bit-o-magic in a box somewhere that keeps track of G forces, how could GPS interfere? Waiting to be educated...:uhoh:

[IO540]

Has there ever been a proven case of interference with aircraft systems from a passenger carried device? References please.

Last i read on this, there was a reported case of laptop interference in some 757 and Boeing even sent up the plane afterwards, empty of course, with the laptop to see if they could reproduce it, and couldn't.

I have been developing electronic products since the 1970s, hardware and software. Much of the stuff written above about susceptibility to EMI is nonsense; if it wasn't there would be transport planes crashing everywhere because there will always be a few people leaving their phones on.

Having a no-gadget policy is fine as a policy but claiming it has a proven technical basis is bogus.

[Techman5]

When we develop aircraft systems, we have to pass both EMC emissions and susceptibility tests. The FAA are rightly over-cautious about allowing anything on-board that has not been tested for emissions. This is applied to test flights and limits the test equipment we can use, which can be a pain.

I doubt whether any electronic gadget not specifically marketed for aircraft has been tested, and therefore, no matter how low the emissions really are, they will not technically be certified for flight.

Of course, someone back in row 50 in economy is so far from the EE bay that their equipment is less likely to be a problem than someone in first class (or the cockpit).

[Dan Winterland]

Spooky,

My current type, the A320 uses the blended position referencing to the most accurate position, usually the GPS. I used to fly the 747-400 which did something very similar, but just different enough to differentiate the types. I've also previously flown a 747 Classic which used a Marconi FMS900 fed by receivers various and a Litton IRS (Type unknown). The Litton was position updated by the FMS, usually the GPS position. Also, I've flown a military large type which had a military FMS800 (can't remember the manufacturer) fed by what was known as an EGI. Embedded GPS IRS which did update the IRS position from the GPS constantly and was the most accurate system of all.

[Blacksheep]

Since they have been mentioned in this thread, I make this post about them, rather than the Garmin type GPS receivers that started the topic.

In Brunei, the mobile phone system is crude, to say the least. The handsets are always making search transmissions and at full power. When they can't get a response they ramp up the power and try again. At high power outputs the transmission power is sufficient to break through on my tape player. Yes, you read that correctly, the tape player. It produces a deafening burst of sound so loud that it makes an unsuspecting passenger jump.

Now, in an aircraft, if you leave a mobile phone switched on, it will still search for a pole to link up with. Even over the ocean. Transmission power that is sufficient to be picked up and amplified by the pick-up in a tape player will definitely cause interference to aircraft electronic systems. Unless and until they fit mobile phone transponders into aircraft to allow the phones to connect on low power, let there be no confusion. No-one can safely leave a mobile phone switched on in an aircraft.

[Spooky 2]

Your key words here are "update the IRS position". It does not up date the IRS. I'm amazed at how many people hold this misconception. The GPS signal is used to upgrade the FMC position, not modify the IRS position. As you have stated, the FMC (FMS) takes all this information, weighs it for logic, and then applies it to the FMS position. Typically you can look and see what nav reference is doing the heavy lifting to come up with your position.

If you were flying in a non-GPS equipped aircraft, there would be a limit on how many hours you could operate without some sort of FMS update, typically a VOR, before you could continue. In the GPS equipped aircraft this update is faily constant except at very high latitudes, thus on the B777 the time of operation is limited to 24 hours and not likely to effect any stage lengths in todays operations.

[SNS3Guppy]

We have three INS units, two of which are managed through a FMC, and crosslinked. Each INS has it's own dedicated GPS GNS input directly to the INS and the FMC has it's own GPS input as well.

The third INS, a Litton 92, has a dedicated GPS input which we also don't see. the Litton is only good for (I believe) 6 hours Class II without the GNS input, but it's good indefinitely with it. It doesn't work through a FMC or FMS; it's autonomous and has dedicated GPS input to the INS itself.

[Spooky 2]

Perhaps, but it is not updating the LTN92. It may be updating the position that is derived and displayed but it does not update the IRS.

[twistedenginestarter]

In the GPS equipped aircraft this update is faily constant except at very high latitudes
Why's that then?

[el_visigodo]

GPS signals are extremely weak - less than the ambient noise level.GPS signals are "extremely weak" because they are modulated in direct-sequence spread spectrum (DSSS), that is why they can be under the ambient noise level. They are coded Code Division Multiple Access (CDMA). GPS was a military development and the system is designed to a high jamming margin against intentionally jamming. It is highly unlikely or impossible that one GPS receiver can unintentionally be jammed or blocked by spurious emissions of another GPS receiver on board.

I once used my GARMIN handheld GPS on board a A320 in mid flight to get some waypoints, but I had asked the captain before and he approved it.

[Dan Winterland]

Spooky, you're talking semantics here. My (basic) Litton 92 notes tell me that the IRS position can be updated by an external source. In the fit I was referring to, this souce was the FMS900 which excluded the radio nav aids if the GPS source was accurate. Threfore as far as I'm concerned, the IRS is being updated by the GPS. And as far the EGI is concerned, it's a combined position. An IRS position enhaced by GPS or a GPS position stabilised by the IRS? I don't know. But it did receive the encrypted Y channel GPS signals, so it was in a different league to the fit on airliners.

[SNS3Guppy]

Perhaps, but it is not updating the LTN92. It may be updating the position that is derived and displayed but it does not update the IRS.


Actually, it is. The Litton is taking the GNS inputs, using them for updating, and providing a continuously updated and corrected position using those inputs. It is not processing through a FMS or FMC. The INS is not inputting as a sensor into a multi-sensor unit which then combines the signals. The GPS inputs to the Litton to update it, and the Litton provides the position.

[BEagle]

Dan, it was the Rockwell Collins FMS800.

The Embedded GPS / Inertial Navigation System did indeed include a Y-code capable GPS as well as a Laser INS. But that was only a small part of the sytem; unfortunately the system which you and I were familiar with was only a partial version of the full version used on the Pacer Craig KC 135.

The 'heart' of the system was the CDU. This allowed the navigation method to be selected from either INS1 (the LINS) or INS2 (the old Carousel IV). Either could also be blended with GPS, or, in extremis, GPS-only was possible. However, using a steering signal from GPS-only often causes aberrant heading demands as the system updated, so should not be coupled to the autopilot in NAV mode.

If the whole thing went tits-up, it was, of course, still possible to bypass the CDU and use the old C-IV to drive the autopilot - always assuming that the food-powered interface device had backed up the waypoints correctly. Some of them simply couldn't be bothered.......

And, just for old time's sake, I give you:

http://i14.photobucket.com/albums/a341/nw969/VC10Mod1527-1.jpg

'Snake' banned anyone from ever rubbing it off the board - it was still there when I left!

Your Cat Question for the day - what's in the unlabelled blue box on the left of the photo?

Regarding the use of 'High St.' GPS in airliner cabins, when I first had my Garmin nuvi 660 (no FM transmitter and Bluetooth disabled), I studied the in-flight magazine on board the aircraft in which I was travelling. Nowhere did it say that GPS was not to be used - and I had also read on PPRuNe that many airlines will allow passengers to use such things in the cruise when the belt signs are off. So I started using it - only to be told it was "Verboten!" by the Chief Girl. S/He said that "was the rule", but when I asked him/her to show me, s/he declined.

Since you left for foreign parts, handheld GPS has become almost as common in the UK now as cellphones were a few years ago. So you can expect more and more people to want to use them in flight - and yes, they do work - the top speed recorded on mine is 580 mph!

One of these days I'm determined to see how it copes with this:

http://i14.photobucket.com/albums/a341/nw969/magicroundabout.jpg

:eek:

[radeng]

GPS has a spreading gain of 20,000 times. A 'good ' receiver, even if direct conversion, won't radiate more than 2 nanowatts IF it meets reasonable standards. The GPS signal is a long way down on that. The problem comes with anything that doesn't meet reasonable standards for radiation, and there's a lot of CE marked stuff where the CE stands for Chinese Export. A good professional GPS should never be a problem - it's the cheapo cheapo that might be. Regrettably, we have a whole load of European rules on these matters that aren't enforced anywhere except Germany.
There have been some documented cases in the US where the use of portable VHF FM broadcast receivers on airliners has interfered with the VOR because of the relatively high levels of local oscillator radiation allowed. There was a very good article some years back in the IEEE Spectrum magazine on that.

[Spooky 2]

Thanks Dan and Guppy. I'm going take your word for this GPS/IRS updating until I learn something new, which hopefully at this old age I can still do. Very interesting and Thanks Again!

[411A]

Good God, some here are still complaining about GPS being 'switched off' by the US DoD.
Get over it, ain't gonna happen, full stop.

Can it be used stand alone on the north Atlantic, as a primary means of navigation?
You bet...and I have done so many times.
Dual (or triple) Honeywell HT9100 units have been thus used for over ten years.
'Tis a fact.
Can an INS/IRS be updated with GPS?
You bet, as others have correctly indicated.

And as for BEagle...of course it was a Collins unit, the best there is, bar none.
Except:rolleyes:...perhaps for Hamilton Sundstrand, the heart of the L1011 FMS.
Ahhh....Lockheed!

[Life's a Beech]

An INS update includes an alignment to true north. That's why it must be done stationary and takes several minutes - it is detecting the rotation of the Earth. That can't be done with GPS!

OK, so technically there have been tests with GPS in each end of an aircraft to find heading, but it is nowhere near as accurate as fine alignment on an INS or IRS.

[IO540]

The handsets are always making search transmissions and at full power. When they can't get a response they ramp up the power and try again. At high power outputs the transmission power is sufficient to break through on my tape player.

Is the above for a GSM network? Surely not. AFAIK GSM phones remain silent until they pick up a signal from a tower. Then and only then they run the protocol with that, at a power which is adjusted according to how strong the incoming is (stronger means less power is required from the phone).

I still don't believe there is a significant chance of a mobile phone interfering with anything.

Which is a different thing from banning them as a precaution....

[Self Loading Freight]

Shame there isn't a GPS Receiver on the market which could use the US, Russian and soon to be Gallieo systems for error checking and failure warning.

There will be, just as soon as GLONASS and Galileo are reliable - or, indeed, exist. GLONASS is still recovering from being left to rot in orbit, and has very poor coverage over most of the world - less than 25 percent availability in lots of places. There are also questions over whether it'll adopt GPS compatible signalling. It's not yet stable or reliable enough to support.

Galileo is still a long way from being operational at all, but I know that GPS receiver makers are intending to include Galileo capabilities. It won't be difficult or expensive when the time comes and there's no real reason not to, but the designers aren't sure how useful it'll actually be.

R

[NSEU]

"I have to call you on that one. There is no IRS/IRU/ADIRU that updates from any external source...in any civil aircraft, be it Honeywell, Litton, etc. The FMC (FMS) will up date from GPS/DME/LOC/VOR."

Many years ago (pre-FMC), we had direct DME inputs to our 747 Classic INU's. Note that INU's are different from IRU's in that INU's have full navigation capabilities. IRU's require FMC's.

However, I guess you could argue the definition of "updating". During DME updating on our Classic 747's, DME-only position is used for navigation (not the inertial position), although the two values are compared for reasonableness inside the INU. You could say that the DME is not really modifying the basic inertial position, but the INU itself is outputting more accurate (DME) data.

This system was very labour intensive and involved manually inserting DME station info via the CDU.

Rgds.
NSEU

[Spooky 2]

Was that a Collins AINS70 by chance?

[Dan Winterland]

Blimy BEagle, I remeber that diagram. Was the blue box on the left the oven? The most essential piece of equipment on an RAF tanker!

And as for GPS set being as common as mobile phones, Mrs W actually has a GPS built into her mobile phone!

No GPS could ever cope with the magic roundabout! Reminds me of the true tale of the American exchange officer who on his first excursions onto the British roads happened across the said roundabout. After going round three times, he decided he couldn't get out of it, parked his car in the middle and waited for the police to arrive!

[BEagle]

No, not the oven! It was the JTIDS terminal (used ac posn and air data).

You're right about the oven though - most essential!

I can well believe the confusion the magic roundabout would cause to a US Exchnage Officer - it'd be hard enough for him to remember to drive on the left, let alone cope with the 5 linked mini roundabouts!

[el_visigodo]

GLONASS is still recovering from being left to rot in orbit, and has very poor coverage over most of the world - less than 25 percent availability in lots of places."The full constellation of 24 satellites, scheduled for completion in the next two years, will allow the system to reach users worldwide."

http://www.spaceflightnow.com/news/n0712/25glonass/

[ankh]

Following the pointer from the active 777 topic, for those thinking about electronic interference. There may be no interference at all from one source in one mode, or in any of its modes.

Combining two variable sources gives an inordinate number of possible combinations.

Combining all the sources passengers may have active at any moment gives in inestimable number of combinations.

What do we know about combining a great many waveforms? On a two-dimensional surface, quite a bit, although this work has become a worry only very recently because it explains a problem long considered a myth, until photographs and satellite instruments show it happens:

http://www.ams.org/mathmedia/archive/01-2003-media.html

" BBC Two, on November 14, 2002, aired a program on this phenomenon and its recent mathematical analysis. Freak waves, also "rogue waves," "monster waves," are extraordinarily tall and steep waves that appear sporadically and wreck havoc with shipping. One is suspected to have washed away the German cargo München which went down with all hands in the midst of a routine voyage in 1978. More recently, the cruise ship Caledonian Star was struck by a 30m wave on March 2, 2001. The standard analysis of ocean waves predicts a Gaussian-like distribution of heights; extreme heights, although possible, should be very rare - a 30m wave is expected once in ten thousand years, according to the BBC. But these waves occur much more frequently than predicted. The program focused on new methods of analysis, and on the work of the mathematician A. R. Osborne (Fisica Generale, Torino). Osborne has applied the inverse scattering transform, which he describes as "nonlinear Fourier analysis," to the time series analysis of wave data. He conducted simulations using the nonlinear Schrödinger equation and found near agreement with the standard analysis, except that "every once in a while a large rogue wave rises up out of the random background noise." His paper ... gives an example of such a simulation:

http://www.ams.org/mathmedia/images/wavetrain.gif

See the spike? Put the spike into your onboard electronics. There will be a spike strong enough to overcome the specified sensitivity protection, somewhere in 3-dimensional space inside the aircraft, at some point. Most of them won't coincide with anything that will interpred the spike as a signal. Some of them will. Some of the software won't reject that as an incorrect signal.

On a two-dimensional surface, the ocean, such a spike (rogue wave) can break a long oil tanker in half. The tanker design assumes there are no such waves -- they weren't observed when the designs were established and nobody's tried to reinvent the oil tanker to build one capable of surviving these events. They lose a few, cost of doing business -- until now nobody could do the statistics, they didn't believe rogue waves happened!

The Japanese had a term for this long ago, in a very dense population with a lot of electronics and electrical gear and little in the way of shielding -- "electronic smog."

The first deaths from unexpected activation of electronic equipment due to this were reported over 20 years ago.

http://intranet.cs.man.ac.uk/Study_subweb/Ugrad/coursenotes/COMP10070/KR_real

-----excerpt----
A series of mysterious deaths in which industrial robots suddenly attacked and
killed humans is being investigated in Japan, news reports said yesterday. Ten
people have been killed by robots in the last eight years. In four cases,
operating errors were blamed. In the other accidents, the robots suddenly
started working for unexplained reasons, according to reports. Witnesses
listed a number of cases in which the robot suddenly stretched out its
mechanical arms, killing its victim. Experts plan to test a theory that
electromagnetic waves in factories have been responsible for setting off the
sensitive computer mechanisms in the robots.

[We had previously documented the 1981 Kawasaki case, and noted reports of at
least four more (and possibly as many as 19) robot-related deaths.]

http://catless.ncl.ac.uk/Risks/4.91.html#subj1.1
CHIPS ARE DOWN OVER ELECTRONIC POLLUTION
The Guardian, 26 May 1987
"Lindsay F. Marshall" <lindsay%[email protected]>

Japan is engulfed in an "electronic smog" which has caused deaths and injuries,
and jammed an airport radar system, according to recent findings.

Electronic smog occurs when electromagnetic waves from equipment like personal
computers and electronic game machines "escape" and trigger other machines. An
electromagnetic wave can also be caused by a mere spark. An electric spark
from a crane operating in a valve plant set off a lathe-operating robot in
1982 killing an assembly-line worker.

http://catless.ncl.ac.uk/Risks/2.42.html#subj1.1
Date: Mon 14 Apr 86 09:19:46-PST
From: Ron Cain <[email protected]>
-----end excerpt------

Remember -- the more signals you have, the more they will overlap, and the energy in the waves is additive so you _will_ get 'rogue' spikes of very strong signal that come from no identifiable individual source -- they come from the interaction of many signals that is momentary and not reproducible.

And we're at a sunspot minimum right now, so you can't blame it on sunspots. In a few years, though, those will be adding to the effect.

[Self Loading Freight]

While it's possible for lots of different EM radiating sources to coincide and produce unusual peaks of energy, that would be extremely difficult to categorise in any useful way other than by observation. My head hurts with the idea of creating even a crude mathematical model of an aircraft full of bored punters playing with their gadgets. I've seen how researchers model office conditions for WLAN design, and even when you're limiting the radios to one design doing one job on one band, it's devilishly difficult to get useful answers - at one point they started to put sacks of saline solution in the chairs to model absorption by bodies - and the speed at which technology changes means you can't spend years trying all these ideas.

But that doesn't mean it's not possible to get useful results. Ideally, the aviation and ICT industries would work together to create and run a testing regime that models real life as closely as possible.

[BobT]

IO540 nails it.

While the theoretical discussion is interesting, we've by now a good amount of practical experience that strongly indicates that EMI from consumer devices isn't much of an issue if any.

Think about the numbers of emitters (mobiles, laptops, Playstations, digicams, DVD players, Ipods, etc. etc.) that have been used in all phases of flight. No aircraft down under mysterious circumstances...

[ankh]

> While it's possible for lots of different EM radiating sources to coincide
> and produce unusual peaks of energy, that would be extremely difficult
> to categorise in any useful way other than by observation.

It's more than 'possible' -- it's physics. It happens.

Look up the very new field of research on 'rogue waves'

These are being described now in light and other electromagnetic terms as well as on the surface of the ocean. Once people realized these things really happened and can explain the odd number of losses of the largest ships, and observed them, the research took off fast.

Example, recent work only; some of these likely relate to what's happening in an environment like the inside of an aircraft:

http://scholar.google.com/scholar?num=100&hl=en&lr=&newwindow=1&safe=off&scoring=r&q=rogue+wave+models&as_ylo=2007&btnG=Search

First hit in that search (abstract only, you'll have to visit a library or Google for the authors' bibliography pages or other sources to see more):

http://www.nature.com/nature/journal/v450/n7172/full/450953a.html

Nature 450, 953-954 (13 December 2007)
doi:10.1038/450953a; Published online 12 December 2007

Photonics: Rogue waves surface in light

Dong-Il Yeom & Benjamin J. Eggleton

Abstract

How do the freak waves that haunt seafarers' nightmares arise? We don't know, is the short answer — but the discovery of a similar phenomenon in optical waves might assist in getting to the bottom of the mystery.

Oceanic rogue waves — monstrous sea waves that form spontaneously and can reach up to 30 metres in height— have been held responsible for marine misfortunes ranging from the sudden sinking of seagoing ships to damage to oil platforms. They are not just the stuff of maritime folklore ...

----- end abstract ---
From the related links provided, this:
Nature 450, 1054-1057 (13 December 2007) | doi:10.1038/nature06402; Received 22 February 2007; Accepted 11 October 2007
Optical rogue waves

D. R. Solli1 (http://www.nature.com/nature/journal/v450/n7172/abs/nature06402.html#a1), C. Ropers1 (http://www.nature.com/nature/journal/v450/n7172/abs/nature06402.html#a1),2 (http://www.nature.com/nature/journal/v450/n7172/abs/nature06402.html#a2), P. Koonath1 (http://www.nature.com/nature/journal/v450/n7172/abs/nature06402.html#a1) & B. Jalali1 (http://www.nature.com/nature/journal/v450/n7172/abs/nature06402.html#a1)
Department of Electrical Engineering, University of California, Los Angeles 90095, USA
Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, D-12489 Berlin, GermanyCorrespondence to: D. R. Solli1 (http://www.nature.com/nature/journal/v450/n7172/abs/nature06402.html#a1) Correspondence and requests for materials should be addressed to D.R.S. (Email: [email protected]).



Recent observations show that the probability of encountering an extremely large rogue wave in the open ocean is much larger than expected from ordinary wave-amplitude statistics1, (http://www.nature.com/nature/journal/v450/n7172/full/nature06402.html#B1)2, (http://www.nature.com/nature/journal/v450/n7172/full/nature06402.html#B2)3 (http://www.nature.com/nature/journal/v450/n7172/full/nature06402.html#B3). Although considerable effort has been directed towards understanding the physics behind these mysterious and potentially destructive events, the complete picture remains uncertain. Furthermore, rogue waves have not yet been observed in other physical systems. Here, we introduce the concept of optical rogue waves, a counterpart of the infamous rare water waves. Using a new real-time detection technique, we study a system that exposes extremely steep, large waves as rare outcomes from an almost identically prepared initial population of waves. Specifically, we report the observation of rogue waves in an optical system, based on a microstructured optical fibre, near the threshold of soliton-fission supercontinuum generation4, (http://www.nature.com/nature/journal/v450/n7172/full/nature06402.html#B4)5 (http://www.nature.com/nature/journal/v450/n7172/full/nature06402.html#B5)—a noise-sensitive5, (http://www.nature.com/nature/journal/v450/n7172/full/nature06402.html#B5)6, (http://www.nature.com/nature/journal/v450/n7172/full/nature06402.html#B6)7 (http://www.nature.com/nature/journal/v450/n7172/full/nature06402.html#B7) nonlinear process in which extremely broadband radiation is generated from a narrowband input8 (http://www.nature.com/nature/journal/v450/n7172/full/nature06402.html#B8). We model the generation of these rogue waves using the generalized nonlinear Schrödinger equation9 (http://www.nature.com/nature/journal/v450/n7172/full/nature06402.html#B9) and demonstrate that they arise infrequently from initially smooth pulses owing to power transfer seeded by a small noise perturbation.

------end of abstract ----

Much more information available. Serious, very new science being done.

One last thought -- put the signal generators inside a Faraday cage -- airliner, train, or bus -- and you get intensities above those outdoors.

That's being studied as well, for example:

Electric-Field Distribution Estimation in a Train Carriage due to ... (http://ietcom.oxfordjournals.org/cgi/content/abstract/E88-B/8/3281)

The electromagnetic field (EMF) distributions created inside a train ... A simplified histogram estimation method for electric field strength is newly ...
http://ietcom.oxfordjournals.org/cgi/content/abstract/E88-B/8/3281

How much more or less sensitive is aircraft electronics at any individual particularly exposed spot in the cabin than, say, a cardiac pacemaker?

----abstract---
The electromagnetic field (EMF) distributions created inside a train carriage by the cellular radios of the passengers are analyzed and the impact their electromagnetic interference (EMI) on the implantable cardiac pacemakers is evaluated based upon the analysis results. Both computer simulations and experiments using 800 MHz and 2 GHz transmitters in an actual train carriage confirm that excessively high EMF, high enough to affect the normal functions of the pacemaker, does not occur inside the carriage provided the safe distance of 22 cm specified for pacemaker users is kept. A simplified histogram estimation method for electric field strength is newly developed to deal with the complicated EMF distributions. It allows the EMI risk to pacemakers by cellular radio transmission to be quantitatively evaluated. Methodologies are described first. Typical results of FDTD analysis and actual measurement data are then shown. Finally, considerations and conclusions are made.


---end abstract----

So -- there's more science news every day. Opinions don't change nearly as fast as what's actually known. Always worth looking up what's known, today, compared to yesterday.

[rossmi]

Following on from this discussion ... is it known to what altitude the 'electronic fog' might affect an aircraft's equipment? I'm researching the vulnerabilities of GPS for a security project and am trying to get a handle on the risk of interference.

There was a post in a thread in 2002 ('GPS jamming over most of UK') which mentioned a faulty GPS receiver jamming all other receivers nearby. A brief web search suggests that any Government road toll scheme would motivate many car drivers to use GPS jammers - to avoid being tracked. :uhoh: Would this 'electronic fog' in the L-band affect all aircraft, perhaps, or only at aerodromes close to motorways? Can anyone offer some suggestions?

Then there is the possibility of GBAS being tripped by 'electronic fog' near its GPS receivers ...

thanks

[Geezers of Nazareth]

The use of a GPS device on an aircraft in-flight (or on the ground, if it comes to that) interests me. I have a small GPS which I have used on a flight back from Paris a few years ago, and I still have a copy of the 'track' flown from gate to gate. It only really works if you place it by the window, so that it can 'see' the satellites.

In March last year I was in the USA and did a little flight in Arizona. I asked the pilot if I could use my GPS during the flight, and he was quite happy with it. In fact, he suggested placing it on top of the instrument panel so that it would get a better signal. During the flight I asked the pilot about possible interference, and we moved the GPS around several times, trying to get a reading on any of the instruments. Nothing, nada, zip!

On long distance flights I get bored, so I like to look out of the window and look at various features on the ground below. Later, if I'm able, I try to find these things on Google Earth, to see what else I can find out about those places. Having a GPS makes it so much easier. I can record a location (or 'waypoint', or POI, in GPS terms) for later use.

I find that the moving map display on the 'in flight' entertainment system is completely useless, and nowhere near accurate enough for what I want to do.
As somebody suggested above, do you seriously expect me to go and knock on the cockpit door to ask the pilot for a lat/long readout?? How about if I do this every 30 minutes over the entire flight? How long do you think they would continue to answer the knocks on the door?



There is a product on the market which I have been considering. It is called a 'Trackstick'. It is a small GPS receiver with a memory; it can be programmed to record its location every 1 minute, or every 5 minutes, or every hour, or whatever. Later, the whole set of location recordings can be downloaded for later use or analysis. There's no display on a Trackstick, so you can't instantly see where you are.
So, with a suitable Trackstick placed next to the aircraft window, set to record its position every minute, if I see anything of interest on the ground below I just need to make a note of the time and what I saw, and when I download the data from the Trackstick I can match the two to see where I was.



Going back to my original comments - my GPS device is a small grey box about the size of a box of matches. It uses Bluetooth to communicate with my mobile phone. So, I set the phone to 'flight safe' (as allowed by the airline), and use a Bluetooth connection (also as allowed by the airline) ... what am I doing wrong?

[Dream Land]

I'm no technician but I would say what you're doing affects no one, I know several pilots that do the same thing on the flight deck, happy navigating. :}

[ModernDinosaur]

An interesting anecdote regarding GPS. One system I used about three years ago had two GPS receivers and checked one against the other. One day, receiver 'A' reported no satellites were visible, while receiver 'B' showed a sky-full, albeit it slightly reduced signal level compared to normal. We tried changing the antenna on receiver 'A' for a known-good unit, but still couldn't see any satellites. We scratched our heads for a bit until I suggested using the antenna we'd just removed on receiver 'B' instead. That one change brought BOTH receivers back to life, with strong signals from all satellites. A lab investigation showed that the low-noise amp in the antenna which was originally on receiver 'B', the one that appeared to be working, had developed a fault and was acting as an oscillator which was blocking the other antenna, located some 20m away.

Now imagine your personal GPS has a similar fault. You're sitting in the cabin of an airliner satisfying your curiosity by looking at your moving map, oblivious of the fact that your kit is interfering with the aircraft's GPS. Not a problem in a light aircraft since generally the pilot knows full well that someone in the back seat is using a GPS and can ask them to turn it off if they have the slightest suspicion of a problem. How about the Captain flying 200+ passengers? He or she has absolutely no idea why his GPS doesn't work any more - and if in IMC, they may not even be aware that it's not working.

In general, during critical phases of flight (loosely those which occur within 10,000' of the ground for an airliner), I make darned sure that all of my personal electronic devices are turned off if they can be. I do draw the line at my wrist watch, and if I had one, I'd probably leave my pacemaker on too ;)

It appears from the accident rate that the risk is low even for devices which are designed to transmit (e.g. the infamous cellphone), although there is a growing body of evidence that non-critical system interference does occur fairly regularly. But why take that risk? Is a text message really worth 200 lives?

[ex jump pilot]

Re in flight mags and using "electronic equipment".
I've flown with BA a few times.... Their in flight mag* (plus web site) says that receivers are fine once the seat belt light is off. I've used my GPS on many flights with subsequent enjoyment when the results have been plotted. Can't always get a signal from a window seat but mostly it's fine. N Atlantic to Denver last month wasn't too hot nor was LHR to LAX last April at times. Brazil to LHR gave a wonderful track all the way overnight (had the GPS between the blind and the window).

Considering most receivers are run from a 1.5 or 3 volt battery, I think they would be hard pressed to generate much interference. LCD screens generate noise (my air band radio will pick it up within about 18" (say 45 cms) of my lap top and personal organiser. Somehow, I don't think that would be strong enough to affect equipment in a modern aircraft.

As for mobiles. They have considerably more radiated power and I reckon it's not a good thing to leave one on. However, I suspect aircraft are more than resilient enough against them.

The "test reports" about RFI and aircraft that I have followed up seem very dated and use language that appears to be deliberately ambiguous.

Lastly, whilst it's no bad thing that all "distractions" are put away during landing and take-off, I think it's a bit "we love telling you what to do" by stating no mobiles are to be on until you are safely inside the terminal. Probably more to do with emptying the aircraft faster for a speedier turn around?

One final thought. In the 1930s, death rays against aircraft were wildly popular. Is there a resurgence?

* I think that easyJet also allow receivers to be used. Will be having a go next month though the route is pretty direct so no surprises there.