IO540

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

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

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Chevvron, ignoring out of date GPS databases, INCORRECT use, etc.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

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

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?
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...