Could a handheld GPS interfere with the INS system?
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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.
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.
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This is unlike waking into a store and picking a unit off the shelf and using it in a plane.
The GPS systems I am referring to are ones designed and certified for use in aircraft.
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Small point of order here but GPS nor any ground based nav aids actually update INS.
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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.
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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.
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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...
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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.
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.
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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).
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).
GPS updating of IRSs
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.
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.
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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.
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.
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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.
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.
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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.
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.
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GPS signals are spread spectrum
GPS signals are extremely weak - less than the ambient noise level.
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.
Last edited by el_visigodo; 15th Dec 2007 at 15:49.
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.
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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.
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:
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:
'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?
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:
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.
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.
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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!