Gps

[DFC]

The US Air Force requires IFR flights to have an alternate when;

8.4.2.1.1. All compatible approaches require radar.
8.4.2.1.2. GPS is the only available NAVAID.
8.4.2.1.3. Required NAVAIDs are unmonitored.
8.4.2.1.4. When the destination has no weather reporting capability.

Now radar can go U/S, Unmonitored naviads can be U/S and one may not know, having no weather reports is not great when IFR. All good reasons for having an alternate.

However, GPS?

Isn't that the navaid that it owned and operated by the US military who have access to all it's bells and whistles?

Isn't it the most accurate and reliable bit of equipment that even a simple UK PPL can use for navigation - in fact if IO540's and other's comments are to be believed it is always the best thing available.

Then why does the mighty US Air Force put restrictions on it's use above the restriction thay place on a simple VOR or ILS?

Ideas anyone?

Regards,

DFC

[reynoldsno1]

Isn't it the most accurate and reliable bit of equipment that even a simple UK PPL can use for navigation - in fact if IO540's and other's comments are to be believed it is always the best thing available.

If we assume a simple UK PPL has no IR, then the answer is NO. The most accurate and reliable bit of equipment is your eyes, and GPS will only ever be a supplementary aid.

GPS may be managed by the USAF, but this does not mean it was designed strictly for aviation use - far from it. Aviation users are a minority group. The use of GPS in the aviation IFR environment is problematic, and has many facets. One of the crucial factors is integrity monitoring, and the integral GPS monitoring system does not meet aviation requirements - no secret, and a long known limitation. Equally, GPS is prone to jamming due to the extraordinarily low signal strengths involved. No secret, and a long known limitation

GPS IFR receivers & systems use a number of autonomous methods and/or augmentation to overcome these limitations, and operational requirements are put in place as a safeguard. The USAF ops requirements do not seem to be that dissimilar to civil legislation in many countries that have been using GPS IFR approaches for many years. In my own experience, those safeguards have rarely been required - but the operating environment is considerablely different to radar soaked Euroland.

GPS is not some sort of all encompassing navigation panacea - especially for the aviation segment. But it DOES work 99% of the time - you just have to understand how it works, why it sometimes doesn't work, and have a plan for the latter. But that applies to a lot of things other than GPS

[Chilli Monster]

This is just an aircraft operating and planning SOP which makes pefect sense (alternate requirement) and as such is not, as you suggest DFC, a restriction on GPS use.

[englishal]

Your eyes are not the most accurate. From 20,000' are you telling me you can pinpoint the precise peice of ground you are over, accurate to probably 10m, but certainly 100m?

GPS monitoring is far better than "simple VOR or ILS"....let alone NDB. I've seen a perfectly servicable ILS, which I was flying down on autopilot distort due to another aircraft on the ground. This sent the autopilot chasing the needles, and induced a pretty strange oscillation in close proximity to the ground. No warnings at all.

Anyway, soon we'll be able to fly the "virtual" glideslope in most of the world....other than the UK. Probably because old ex-RAF navigators sit on the boards that make the decisions. You're not one of those DFC are you?

[IO540]

the integral GPS monitoring system does not meet aviation requirements - no secret, and a long known limitation

Oh dear here we go again. Reference please.

As for DFC's post, nobody would rely on a single means of navigation, whatever it is. What's the news?

[wet wet wet]

I seem to remember reading somewhere that the redundancy of the GPS system is falling to critical levels due to the disruption of the satellite renewal programme caused by the space shuttle problems. Each satellite (if I remember correctly) is built with triple redundancy, but several are now operating without any redundancy at all and so could fail at any time. Could this be an issue?

[IO540]

several are now operating without any redundancy at all and so could fail at any time

Yes, but where is the backup for MAY, CPT, BIG, (list of the world's VORs), (list of the world's DMEs) etc?

People accept the old style nav methods and devices without any backup, but GPS is criticised because the massive redundancy might be somewhat reduced.

[FullyFlapped]

Ah, I see DFC is playing his favourite game of "IO540-baiting" again ... oh, and look, he's got a bite ! :p

FF :ok:

[IO540]

...................................... :ok:

[capt.sparrow]

Aviation use of the GPS satellites uses the unauthorized user signal. Therefore the US have the ability to 'shift' the data sent to your gps receiver and so your receiver thinks it is somewhere else (try using a civilian gps receiver in Iraq right now).

In response to back ups for VOR and DME etc - they do monitor themselves and if in error will switch off - you know they've done this as you lose the ident of the facility. There is no such ability for you to check the integrity of the satellites you are recieving. Differential GPS can assist in precision approaches but this is not available over here. GPS is approved for RNAV in europe but again must only be used in conjunction with raw data monitoring of the aircraft position.

[Flyin'Dutch']

GPS is approved for RNAV in europe but again must only be used in conjunction with raw data monitoring of the aircraft position

Are you sure?

I can not recall that this monitoring is required for en-route use of GPS.

There are GPS approaches in Europe. There is more to Europe than the UK

:}

[IO540]

Aviation use of the GPS satellites uses the unauthorized user signal

GPS is approved for RNAV in europe but again must only be used in conjunction with raw data monitoring of the aircraft position

The TUBS* number for this anti-GPS thread is already up there with the best, and we are still on the first page.

* Total Utter B0ll0cks Score

[mad_jock]

Aye you are meant to use the raw nav data to back up all the other whizz bang nav kit.

Its in our part A that we have to. Usually its only displaying the vor's/DME that we have selected on the MAP mode and they should overlay where the GPS thinks the point is or roughly where the VOR is if its off the track. If they don't overlay we have to trust the VOR not the GPS. The scary bit is when the GPS is saying your tracking what the NDB plate says to the beacon and your RMI is pointing that you are off by 15 degrees. Legally you have to follow the RMI.

And i think the other poster was on about the 2 signals which are broadcast from the GPS sats. The main signal which the US goverment can fanny around with and alter the timing of which increases the error. And the second encrypted signal which then tells the military GPS what the fanny around factor is with the first signal to cancel it out. To my knowledge they stopped the fanny around factor a few years ago because the mil sets where to expensive and everybody had bought civi models for personal use in the field. So if they fanny it around the troops don't know where they are either.

Personally I don't have as much faith in GPS as IO540. Its a good tool in the tool box. But it has its issues.

MJ

[IO540]

MJ

You are describing a procedure in your company manual, presumably approved by the CAA under your company's AOC. What you describe is unsuprising, for a public transport AOC manual.

I don't know anything about AOC manuals but I heard from a pilot on one of the low cost airlines, flying an NDB approach, flies it using the INS but they are supposed to check they are within 5 degrees on the RMI (ADF) before descending from the FAF; they are allowed to ignore the NDB after that, until the MDA. This is just another example of a CAA approved procedure (B737) which differs hugely from standard IR training.

There must be loads of these manuals around, with different procedures for different things. Like the USAF one mentioned earlier.

But we are not talking about AOC ops here and CAA approved manuals. The context is private flying, around Europe, and the safest way to navigate.

What others have written, here and elsewhere, is that usage of GPS is variously illegal or unauthorised, and similar legal-looking statements. Every one of those statements is complete b0ll0cks. Even if some look like they come from somebody employed by the CAA.

Less complete b0ll0cks would be a statement that GPS can fail. Of course it can fail, anything can. So anybody with a brain will fly GPS/VOR/DME. Did I ever say anything to the contrary?

The GPS bit will be working perhaps 99.9% of the time; I've had about 2 minutes of non-function in 500 hours which is 99.994% (KLN94). The VOR will be receivable anywhere from say 50% of the time (UK-style VFR or IFR, especially OCAS, or in many places abroad, all depending on how much you like to compromise the route to lie on VORs) to say 90% (ATS routes in low level airways), but on airways flights you will often get a DCT to a VOR which is way outside its DOC - as you presumably must know, looking at your job. Unless you refuse any nice long DCT legs offered by ATC. Maybe you do, so you are always within the DOC of something. Otherwise, much of the time, a BRNAV GPS (or an INS but that's irrelevant to GA) is the only thing that will give you the track guidance to the waypoint given. As for DME, similar comments as for VORs and in addition there are swathes of France where the only DMEs are the low power ones on ILS airports. Surely I am teaching you to suck eggs here!

You mention Selective Availability. At most, SA introduced an error of hundreds of metres. Irrelevant for en-route aviation. Much more of a problem running TomTom in the car though :O

SA was removed over 10 years ago. It was removed not because the mil sets were expensive; that's complete nonsense, but because the military have in-theatre jamming capability coupled with their own anti-jam receiver technologies (e.g. combining a FOG with a GPS and special antennae; very cheap with so many smart bombs carrying the stuff).

GPS is far and away the most reliable nav device available to man, with the added bonus that its failure is generally very obvious.

There has to be a limit to how much time somebody on here will spend repeating the same old obvious statements.

[reynoldsno1]

Oh dear here we go again. Reference please
I don't know what you mean by this. Basic fact - the GPS ground segment has its own integrity monitoring system, but due to the physical location of the stations around the world alerts can take some hours - no good for aviation, hence the development of RAIM and its equivalents, plus SBAS and GBAS. These developments were mainly to resolve the integrity issue, along with an improvement in accuracy.

Hey, it works..... and I think if you read my post again you will find we are on the same side.....
:ok:

[mad_jock]

Calm down to a panic. All I said was I don't have as much faith in it as yourself. In my experence its not as good as your experence.

Still use it everyday at work.

But hey I am only a commercial pilot and have never had the fancy GPS you have, just an old trimble to play with mostly.

INS is a slighty different beast being totally internal to the airframe. With redundacy built in with 2 if not 3 units all cross checking each other and also cross checking using DME crosshatches.

And its a legal requirement you must be within 5 degrees of the final approach track according to the RMI before commencing your decent on a NDB approach. I don't have a clue if the CAA has deemed the risk of the INS all wandering off without indicating a failure in the final approach phase is low enough you can ignore the RMI.

I have never heard of anyone who is allowed to do that when there is a difference with the GPS and the RMI you follow the RMI.

As you well know its a politcal policy more than anything. Until it stops being one, the regulation stops you ustilising GPS to its full manner. There are european boffins that know alot more about the risk assesment than us are saying it isn't good enough at the moment with the lack control over it that Europe has. Any Mil flight can at the moment jam GPS with out telling anyone. FRA are payed to do it whenever there is an exercise on. Until the regulations change so they can't there is still a risk so we have to use stuff they can't fanny about with.


Here is a link to the real stats on whats happening with the GPS network and its errors from the stats

http://www.schriever.af.mil/GPSSUPPORTCENTER

And you can see by the Advisories that they are having a fair few problems. I bet the shuttle not flying has set back there update program somewhat. The page shows that atleast 5 out of the 24 sats are out of action and thats just this year. Not much error so far but... all it would take is a few more and..

MJ

[Chuck Ellsworth]

AAhhh, nothing changes here it seems.

GPS.....Hmmmmm is it accurate?.... is it reliable?

I have only been flying IFR since we used the radio range and the last time i flew IFR was as a crew member in a 767, it didn't have GPS nor INS..it had RNS.

However for me I like and trust GPS, far more than ADF, VOR etc.

But then what do I know about flying? :=

Chuck E.

[High Wing Drifter]

There is a backup for GPS, but I fear the US would get a little antsy. I understand that GLONASS is not yet permitted for civil use, but are there any receivers on the market that use it?

http://www.glonass-center.ru/frame_e.html

http://www.geog.ubc.ca/courses/geog470/notes/background_docs/russian_gps.pdf

[BEagle]

Somehow I guessed that you were one of the original 'Riders of the 4 Course Radio Range' listening for As and Ns, Chuck!

Did you really 'keep to the right' in IMC to avoid collisions before the days of IFR semi-circs?

I use GPS as a back-up as ours aren't IFR-approved. Plus we've had our share of RAIM warnings.

It'd be intruiging to know how many NDB approches really were within 5 deg of the deefining course when flown by little spamcans with suction driven DIs set against a swinging liquid compass - and with only an RBI.....

In my old 'day job' aircraft, we had Y-code GPS blended with laser INS. If you could persuade the lazy $od to do so, you could get the navigator to set it up with the NDB approach course as a course to steer to the beacon position, and then, in some aircraft, display it on the HSI CDI bar. Only as a back-up, of course - we still had to use the RMI for approach guidance. But it was reassuring to see the flickering, twitching RMI backed up with nice, steady 'on-course' CDI indications.....

[Say again s l o w l y]

An interesting discussion here about RAIM outages.

http://www.pprune.org/forums/showthread.php?s=&postid=2173229#post2173229

[mad_jock]

I down loaded the almanac today in the cruise.

Seems there are 30 sats online just now 24 good 2 bads and the rest spare.

Did they ever sort out that registry overflow problem with them? I seem to remember a New scientist article on the subject of the life span of said network.

MJ

[JW411]

I come to this discussion late. I too come from the radio range days/SBA/Consol/Loran/Sun Gun/Decca/Doppler etc etc right through to triple INS and Omega.

In my current day job, we use 2xGPS with UNS1K FMAs as the primary BRNAV requirement. It works very well.

It is categorised as RNP5 equipment. This means that for 95% of a flight, the equipment is guaranteed to keep the aircraft within 5 nms of track.

My fun aeroplane is equipped with a Garmin 430 which I love but when I am crawling round the London TMA, I assume that even if it is as good as the kit I use in my day job, it is only guaranteed to the above limits. I therefore try to give everything a miss by at least 5 nms just in case I'm in the 95% of the time and not when the error could be in excess of 5 nms for 5% of the time if you see what I mean!

Looking out of the window helps enormously.

[bookworm]

Isn't it the most accurate and reliable bit of equipment that even a simple UK PPL can use for navigation... Then why does the mighty US Air Force put restrictions on it's use above the restriction thay place on a simple VOR or ILS?

Because of the issue of availability, not integrity. Sometimes GPS isn't available in a way that meets its integrity standards, and it tells you it isn't -- in part because those integrity standards are so high. Thus there needs to be a different sort of approach available.

Availability vs integrity is a trade off. The higher the standard you insist on (and for GPS for even NPAs, the ICAO standard is many orders of magnitude higher than for conventional navaids) the lower the availability. With an NDB, if it's radiating, it's available. That's because the integrity of the navigational output derived from ADF/NDB is so poor.

If your point is that a pilot should never rely on the availability of a single navaid in a mission critical situation, I'm with you 100%. If you're suggesting that the USAF policy brings other aspects of the "reliability"of GPS into question, or its accuracy, then you need to rethink your understanding of failure modes.

[mad_jock]

http://www.newscientistspace.com/article.ns?id=dn8051

Article in the latest additions to the fleet.

Gives the upgrade over the next few years.

Does anyone know about this new exra freq. I take it won't be available until quite far into the replacement program.

And all you needed to know about gps

http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html