The GPS Thread.........

[IO540]

The answer to this is a three letter word starting with G and ending with S :O

[Andy_RR]

let me guess? you've got to 'P' right in the middle eh?

[shortstripper]

Funny how people equipped with G?S still manage to bust airspace?

SS

[SkyHawk-N]

Funny how people equipped with G?S still manage to bust airspace?

But how many people who have GPS (there, I've said it!) and use it PROPERLY have 'bust airspace'?

Skyhawk.

[BEagle]

Very true, Skyhawk-N!

[chevvron]

We in ATC often find when we warn someone they're inside or about to enter controlled airspace that they start arguing 'my GPS says I'm clear' (or something similar).

[Ni Thomas]

That may be a hint for you to check your radar pulse length and beam width ;)

[Johnm]

Hmmmmmm IO540, my handheld GPS has developed the habit of losing coverage in precisely that area, so panel mount OK but otherwise........

[SkyHawk-N]

Chevvron, ignoring out of date GPS databases, INCORRECT use, etc.
I suppose it all comes down to accuracy, exactly how accurate is your radar?

BTW: I never argue with ATC :ok:

[chevvron]

Ni Thomas & Skyhawk N: Beam width and pulse length don't need to be checked; it's video map that matters, and we know this is correct.

Radar is calibrated regularly, so can be proven to be accurate.
I think the problem lies with pilots relying entirely on GPS, and not bothering to cross check with their map; we all carry maps when flying don't we?

[IO540]

Firstly, only a fool will blindly follow a GPS and its controlled airspace depictions. But for some reason the anti-GPS traditionalists always throw this one in. It's a basic lack of understanding, usually based on never having used one.

Secondly, yes reception will be marginal inside a metal cockpit. That's why a rooftop aerial, or one clipped to the top of a window, is desirable. There is no such thing as GPS losing reception in a particular area.

Thirdly, the Ontrack report (not IMV terribly professionally produced piece of statistics but people like to quote it) shows that only about 18% of CAS busts were done by pilots using a moving map GPS. Of the pilots doing real flying from A to B, vastly more than 18% use a moving map GPS, and practically none of them use a non-moving-map GPS (which is near useless as it doesn't deliver situational awareness). The only way you will bust CAS with a GPS is if your brain goes to sleep for a while (which does happen sometimes) or if you made a gross planning error back on the ground (which one would have made with or without a GPS).

This is why GPS usage should be in the PPL as standard.

[SkyHawk-N]

we all carry maps when flying don't we?

I'm sure we all do and checking the moving map GPS with the physical map (with all the lines, Wind speed/direction, waypoints, etc drawn on) takes a second or two every few minutes. The configurable GPS warning of approaching controlled airspace is always a welcome reassurance.

My question about the accuracy of your radar is just out of interest. If you have regular arguments with GPS users there must be a problem somewhere as the experience I have of my GPS is that it is extremely accurate and reliable. How far do you consider the these guys were inside your airspace?

[IO540]

GPS should be a lot more accurate than radar. It's usually within a few metres. Commercial radar won't give you that at say 20nm.

The CAS shapes in the GPS database normally come from the national AIP of the country concerned, where they are given as lat/long coordinates, arcs etc and that data goes straight into the GPS database. Sometimes these are wrong, but it's very very rare. I've never heard of this in the UK, in 6 years I've been flying. But obviously where CAS has changed then unless one has updated the database.....

It's not a good idea to use GPS as the sole CAS shape reference, not because it's wrong but because it's not very clear. If one could get a large panel mounted GPS that displays (in the UK, anyway) the actual CAA charts, that would be great, but one can't buy one.

[Ni Thomas]

Chevvron - But the little blobby target on your magnificent video screen is obtained from a radar pulse and that pulse may not be as accurate as my satellite obtained position (note I do not use the G?S word :\ ).
I'm sure you're right, your video screen may have the CAS lines and things nicely and accurately depicted theron it but that does not mean the moving 'blob' is absolutely correct - That 'blob' does depend on pulse length and beam width of the radar (s) used - An electronics bloke (and I ain't one) Iwould be able to indicate to you the inbuilt positional 'errors' due to the fundemental machinations of the radar emission (eg a conservative beam's width of say 0.5deg will produce a pretty accurate position at 1 naut.mile. but that same beam width, after 'fanning out' for 20 or 60 or whatever nautical miles will produce a rather more inaccurate result. The same goes for the pulse length (but due to the nature of the beast, is normally more accurate).
How many times have I heard Jersey Radar calling "You're crossing 50 North now - Squawk 7000, Change to xxx.xxx"? When, in fact, we've still got 3 miles to run? :confused:
PLEASE, please, please don't force me to go have to climb into my attic to root out my Ladybird Book on "How a Radar works" with it's associated mystical radar block diagrams, and circuitry stuff - PLEASE! my age won't allow! :)

[SkyHawk-N]

Hey I0540, you've gone and done it now! we've been evicted from the 'Lost' thread! :}

[chevvron]

Without wishing to start an argument, I'm sure panel mounted GPS are supremely accurate, but I'm not so sure about handhelds, where the airspace database could be out of date for instance. I'm talking basically of penetrations or near penetrations where the pilot claims he is up to 5 miles away from regulated airspace, and I'm positive it's not the fault of ATC radars, 'cos we often crosscheck with adjacent units and they agree about the position. I dimbly remember a thread somewhere about innacuracies in Jeppesen supplied GPS databases (might have been on another forum other than Pprune).
My own Garmin for instance, is pretty accurate as regards airspace, but the road database seems to only get it right for the M25, other roads being about a mile adrift, but then it's not supposed to be used at ground level anyway without a DGPS signal.
Ni Thomas; the days of blobs on radar displays are long gone; we get plot extracted symbols nowadays which a processer compares with the SSR plot and oh god I'm boring myself TDM take over.

[boomerangben]

Haven't you lot got any flying to do rather than turn this old nugget out again!

[funfly]

Wish I could resist posting on this old nugget again but I'm weak.
Navigate with a hand held GPS from Dixons and you might as well fly altitudes with your household barometer.
1. Panel mounted GPS with external aerial.
2. Use as just another navigation aid, same as your DI, VOR etc.
The more variable cockpit aids you use the better your chances.

[IO540]

Assuming good reception, there is no accuracy difference between a handheld and a panel mount. And either can have out of date maps.

However, one cannot rely on road/rail depictions on the GPS. These can be a mile out. I noticed this very early when driving with one. A bit hard for those that follow roads/railways and expect the GPS to match. What will be right is aeronautical data and that is what matters.

[englishal]

Even a cheap handheld GPS makes a good DME substitute, with waypoints downloaded from the FAA database, which of course are provided FOC....

You can then avoid CAS by flying a DME arc around the waypoint...

[Mike Cross]

Funny how people equipped with G?S still manage to bust airspace?And you'd be amazed how many of them have a knob marked OBS as well.
It's usually the loose nut on the yoke that causes the bust, not the Nav Equipment.

[nipper1]

Great thread. Even more uninformed rubbish than usual.
As it happens I know quite a lot about GPS accuracy (I have spent the last two years deploying GPS in a non-aviation application and actually testing the accuracy of various commercial units both statically and dynamically) but I won't bore anyone here with what I have found out as it would spoil this thread....
Suffice to say, the problem will almost always be with the operator and not the kit - as it was last time I dialed '190' into my VOR instead of '170' and ended up somewhere I did not mean to go.....

[Fuji Abound]

Nipper1

Oh no, please do bore us!

There is so much disinformation written about the unreliability of GPS from the "anti" lobby that I think it would be a great contribution to this thread to read your findings.

[chevvron]

Nipper 1; is it true that GPS for car use depend on a DGPS signal transmitted from commercial radio stations and 'piggybacked' on their transmissions?

[High Wing Drifter]

There is so much disinformation written about the unreliability of GPS from the "anti" lobby that I think it would be a great contribution to this thread to read your findings.
I'll second that!

[funfly]

I flew on a 100 bearing today instead of an 010.:uhoh: nearly went into an ATZ (true story)
Fault of a useless compass of course, you just don't trust them

[Johnm]

For the record I'm a GPS fan. If I've got a panel mount it's my primary nav facility and it works more reliably and more accurately than anything else on the panel including the FM Immune VOR/ILS (which works no better than the none immune one but that's another story)

The only caveat on GPS is the issue of relying on the database to be both up to date and accurate when it comes to airspace (they usually are if regularly updated but not always) so there's a need to xref a current chart and NOTAMs but that's routine flight planning ain't it???

For hand helds extra caution is required because they will lose coverage from time to time depending on how uniform the view of the constellation across the sky happens to be. Early morning East bound near Luton seems to be a problem at present in this respect

[funfly]

Johnm
We're all with you.:ok:

[shortstripper]

for the record I'm not anti-GPS, but still find it rather too all encompassing to say that the "answer" is GPS! Users still bust airspace! Yes it probably is the fault of the user, but it's the growing reliance on GPS that is most worrying. Before much longer it feels like traditional ways of navigating will be dumped in favour of this perfect solution to our navigating woes. As the son of (and myself at various times) a professional fisherman, I can say that the introduction of GPS was a revelation when compared to the old decca system. However, GPS still occasionally loses itself during certain atmospheric conditions, rough seas or electrical circuitry problems. Ok, these are tiny things and most unlikely ... but they do happen. I even remember once (when airbourne GPS first came in I admit) hearing a pilot disputing that he was somewhere other than where he thought. he said something along the lines of "this GPS cost two thousand pounds ... it can't be wrong" to which the controller curtly replied "well this radar cost twenty million ... do you think it is wrong"?

SS

[IO540]

The only caveat on GPS is the issue of relying on the database to be both up to date and accurate when it comes to airspace (they usually are if regularly updated but not always) so there's a need to xref a current chart and NOTAMs but that's routine flight planning ain't it???

I would normally agree you need the printed chart for VFR planning but not for the accuracy. Your chart can be up to a year out, and notams of changes will be in the notam database only until the next AIRAC cycle i.e. 28 days. So if the chart is dated say Jan 06, there is a change 01 Feb 06 and you don't fly the relevant airspace during Feb then you will never know about it. Whereas with GPS databases you have the option to know.

The fact that it costs a lot of money to update is a separate issue, but it can be minimised, e.g. if you are doing a long trip around Europe then you have a choice of

a) buying a load of printed charts, which will be anything up to 2 years out of date

b) updating the GPS database, which will be at most 28 days out of date

For VFR you do both. For IFR (airways) you buy a few airways charts, dirt cheap, and do a one-off database update, but we aren't talking about IFR here.

It's a tough one because CAS depictions on GPS databases have poor clarity; only just good enough to relate to the paper chart on your lap. But, if the two differ materially then it should be obvious there is something wrong.

For hand helds extra caution is required because they will lose coverage from time to time depending on how uniform the view of the constellation across the sky happens to be. Early morning East bound near Luton seems to be a problem at present in this respect

I doubt there is anything in this. There is no correlation between the GPS satellite constellation, early mornings, and Luton :O Maybe you have marginal reception and are getting zapped by radar or something.

A current-model handheld with a rooftop aerial will be as good as any panel mount with a rooftop aerial.

Before much longer it feels like traditional ways of navigating will be dumped

The correct thing to do then is to donate them to the British Museum, not fly with them. My heart really bleeds for these wonderful old traditions.

As I've said before 50 times, there is no way navigation is going to improve as long as people are expected to be doing dead reckoning. Unless the CAA donates £5,000/year to each PPL every year for currency, which it won't. Just about anybody can get a PPL if they are willing to survive a year's worth of UK training, and "just about anybody" isn't going to get any better tomorrow than they are today. The only options left are to more carefully select the pilots (which the training industry will be dead against), train them more rigorously (comment as before), or use different methods. GPS is the best method known by far; nothing comes even close.

[Johnm]

Actually the wee beasty is normally very reliable completely unmoved by proximity to radar or Hirta sites and it's possible that there's gaps in the constellation it can see through the windows 'cos of failed satellites. It used to be perfectly reliable in this particular area too. However I can't claim to be a serious expert in GPS infrastructure.

[IO540]

The constellation isn't geostationary; it moves about all the time. So there can't be location-consistent coverage gaps.

There is a website where you can get coverage quality (RAIM) prediction for a given lat/long location and time, or an IFR GPS can work it out for you. But as I say it varies with date and time.

[englishal]

The constellation isn't geostationary; it moves about all the time. So there can't be location-consistent coverage gaps.
HDOP and PDOP spring to mind........

Which the GPS tells you ;)

[DFC]

IO540,

Your statement regarding updating the aeronautical chart to make it legal is incorrect.

AIP:
Before using any CAA chart operationally, users must determine what aeronautical changes have taken place since its
validity date and amend the chart accordingly. This will require users to consult all UK AIP amendments issued since the charts validity
date. If in doubt, they should consult AIS Central Office. A list of amendments for the VFR chart series is available on the CAA web
site: www.caa.co.uk/dap/dapcharts

It is not a useable chart unless the relevant updates have been incorporated. The CAA website not only lists all changes but will often have advance warning of future changes.

Other countries will have their own system, many of them will include the hand amendments in the AIP. Jeppesen have a chart notam series updated weekly.

IO540 said: There is a website where you can get coverage quality (RAIM) prediction for a given lat/long location and time, or an IFR GPS can work it out for you. But as I say it varies with date and time.

Will your IFR GPS tell you in advance that sattelite 30 will be u/s from 15:15 tomorrow until 03:15 on 1st March?

-------
I can't hear - the medical limitations for hearing are wrong.
I can't differentiate colours correctly - the medical standards for colour blindness are wrong.
I can't navigate by DR - GPS should be the way to navigate.

Deaf, Dumb and Blind pilots should not be discriminated against :D

Regards,

DFC

[englishal]

.....there are a few Dumb pilots on these forums, thats for sure

[boomerangben]

Can't we just make up our own minds about how to navigate? What suits some might not suit others.

I fly SAR. We use GPS extensively. We also make use of VORs, (OK only very rarely but that is due to altitude and location) NDBs, DME and DR (albeit calculated by computer from a Doppler unit). We also spend much of our time eyes out with a chart on the lap. We train to navigate low level over featureless landscape to find a pile of rocks without the GPS. GPS may be accurate enough, but cartography is not. We would be mad to simply use GPS to get us to a casualty at the bottom of a cliff/half way up a mountain. GPS gets us to the ball park then we use the eye ball. The GPS is also backed up by mandraulic DR for gross error checking. In other words all means of navigation have their place in aviation. OK we are perhaps ususual in that we use all of them.

It is vitally important that all VFR pilots can read maps and charts. Learning traditional navigation techniques helps that learning process. Shamefully it is poorly taught at PPL level. Partly because we are all a little bit gadgety, partly because no one taught the instructor to navigate properly, partly because we want to fly not study when learning to aviate. With a little more time, map reading could be made more accessible and easier.

[IO540]

DFC

Like most of your more technical postings, you are describing an ideal world which in practice doesn't happen. Pilox X buys a chart from his local pilot shop and flies with it. He buys the next edition the following year, etc.

Translate that situation to going outside the UK, where you deal with potentially a multiplicity of charts, some (e.g. Greece) not updated for 5-10 years. Electronic databases like Jepp are the only way to get up to date chart data for a lot of places in Europe.

boomerangben

I don't disagree, but in your case IF the person you are rescuing had a GPS and was able to transmit the lat/long to you using some means which doesn't involve speech, your job would be a lot easier. Know about EPIRBs with a built-in GPS? If you can't use the signal then a lot of your capability is pretty sub-optimal.

To clarify: a lot of this pro- or anti-GPS debate is really the modernist v. traditionalist debate. "GPS" just drags the respective protagonists out of the woodwork.

I have no problem with somebody who wants to fly traditionally; it's their business entirely. If you want to fly like Charles Lindberg, right down to wearing exact Lindbert replica underpants, I admire you for the effort and wish you success. I have just spent some time in Arizona, where the most modern turboprops/jets with all the gizmos coexist happily with wood and fabric aeroplanes from WW1, all on the same airfield, and often flown by the same people.

But if the objective is to make a dent in the few-hundred CAS busts that were reported last year, it's no use pretending that "better training" is the answer. Well it might be but it won't come about.

It's equally no use pretending that pilot X is suddenly going to navigate reliably by dead reckoning, when (like most people) he has been having problems with it beforehand.

[shortstripper]

But he/she will buy a GPS and learn how to use it properly?

SS

[DFC]

IO540,

I just love the way you dismiss legal requirements that are easily and simply met as some form of ideal that can be ignored. Obvoliusly you did not ignore that ideal (legal requirement) because you did not know about it. Now you do. Isn't learning fun. :)

You also ignored the comment I made about the RAIM perhaps you would like to anwer that question?

--------------

boomerangben,

Well said.

Regards,

DFC

[boomerangben]

Of course the incidents where we get a GPS derived positions are much easier, but onshore at least, they are few and far between. We are usually relying on Joe Public's map reading abilities. The GPS/EPIRB combination is wonderful though not as widely used as it should. Many of our jobs are onshore or coastal. The GPS is great for getting us to the locale, but for situational awareness, planning the operation and setting up an approach to the casualty's location is best done using an OS map. The GPS will take you to the exact position, but it will not tell you what to look for or indeed if it is the right position. Nor will it tell you that you are about to hit something hard or stringy.

Of course for many PPLs the GPS is adequate, but you can navigate very well without one (in my opinion just as accurately). In some situations the GPS is preferable to map reading, in others, map reading is more suitable. Yes, map reading is a hard won skill, but it is wonderfully satisfying and adds a bit more interest and challenge to private flying.

To say one is better than another is like saying apples are better than oranges. To say that PPLs shouldn't bother learning about a valid nav technique is like not teaching an apprentice carpenter about the different types of saw.

[mad_jock]

here is the euro control link for Raim prediction.

http://augur.ecacnav.com/status.html

The NPA tool is for approaches. And as such can be ignored in the UK.

Another page which may be of interest is

http://www.ecacnav.com/GNSS

It also lists out when all the project should come to pass and what you can expect the end service to be.

And another link from the royal college.

My view is that its a very useful tool in the tool box. It does need backup and a certain amount of training to be provided to inform the user of its limitaions and its failure modes.

As a matter of interest can you get a combined GPS/VPU for light aircraft?

[englishal]

Will your IFR GPS tell you in advance that sattelite 30 will be u/s from 15:15 tomorrow until 03:15 on 1st March?
No idea, but GPS outages will be notamed, and you do check your Notams don't you DFC? I hope so. I don't care if satellite 30 is going to be U/S so lonag as I can still position myself. It is not very often spacecraft just "fail", they may be shut down for some reason, in which case we all know about it in advance - if you care to check.

Actually I believe in the GPS message, satellite health information is transmitted.

[High Wing Drifter]

Will your IFR GPS tell you in advance that sattelite 30 will be u/s from 15:15 tomorrow until 03:15 on 1st March?
Satellite 30? It'll be some system that doesn't report it as U/S. Galilleo isn't a reality yet :8

[IO540]

It doesn't matter if one satellite goes. Most of the time one is receiving as many sats as the receiver is capable of concurrently, 8 for mine.

Playing with the Eurocontrol website MJ gives shows just how good the reception is. Even when there is RAIM outage, this is not relevant to en route navigation. It's relevant only to GPS approaches, but

a) we don't have them in the UK

b) where they exist in Europe, they are merely supplemental to some other approach, and one has to carry all the kit anyway, according to the IFR/CAS requirements in various airspaces

c) in the UK anyway, it will be for ever before we get The One Really Useful Thing (GPS approaches into airfields that don't have any IAP) largely because of the cost (CAA requires full ATC, etc)

Galileo won't be any different; it can't possibly be. The physical reality is still just X sats whizzing around up there. Any guarantees of availability are just empty words from European politicans who are so superior to American ones :O Well, they are not quite empty words, because they will make GPS approach legality dependent on paying for the "higher integrity" signal :O

[giloc]

a) we don't have them in the UK
b) ...
c) ...

Indeed; but at least by May this year we should be able to have a go (in VMC) at the new GPS non-precision IAPs at Shoreham, Exeter, Blackpool, Gloucestershire, and a couple of others.
I think IO is spot-on with c). Even beyond the cost of ATC, creating a new IAP would involve paying a contractor to design the procedure (the CAA's DAP want to hand over the responsibilty for design of IAPs to 'industry'), paying to have it flight checked, and paying again to have the CAA approve it.

[IO540]

Interesting stuff, Giloc. The hugely relevant thing will be if one gets lower minima with the GPS approach than with the existing one.

Otherwise, there is no real point. Anybody can fly an NDB approach using the GPS and I think that's what most IFR people actually do; you check the ADF on the outbound/inbound (to eliminate gross errors) and the rest is flown on the GPS. Then you don't get the awful ADF errors which can be 30 degrees or more (especially at Shoreham) which, if you are to fly as per the book (maintain the ADF track) make you chase the inbound track around so much you are not in a position to make a safe landing when going visual.

[giloc]

Well, I would hope they're designing the procedures around a system minima of 250' aal, so there is at least the potential for lower MDAs.

The procedures are to be published as an AIP supplement, presumably before May.

[IO540]

They will be going down to 250ft without vertical guidance or WAAS/EGNOS??

That is most unlikely. No nonprecision approach can go that low. I would guess 500-600ft would be the minimum, even when there is no terrain around.

[Fuji Abound]

IO540 - correct

It is worth taking a look at the RNAV approach for Lille which was apporved as long ago as June 2005.

Whilst the apporach is for 08 and the ILS is on 26 it does give an interesting comparison between the approaches and the DH.

[giloc]

They will be going down to 250ft without vertical guidance or WAAS/EGNOS??

No. System minimum is not the same as OCH or MDH. The MDH will be the higher of system minimum and OCH. The point is that the system minimum for NDB is 300', so if GPS approaches are based on a 250' system minimum then there is the "potential for lower MDAs".
No nonprecision approach can go that low.

Where the obstacle situation allows the system minimum and MDH can be close. For example, the VOR/DME system minimum is 250' and the Cat A MDH for the VOR/DME RWY 21 at Biggin Hill can be as low as 300'.

[chevvron]

Minimum obstacle clearance for non-precision approaches is 75m/246ft (ref ICAO Doc 8168 Pt 2)

[IO540]

A 250ft MDH GPS IAP into every GA airfield would be wonderful... it will never happen for the reasons given though.