Use of GPS

[Currymonster]

Having recently acquired a Garmin iii, I wonder how many rely solely on this gadget.
I find it very useful but find myself going out of my way to obtain position fixes visually and QDM's in order to confirm position, seemingly paranoid in not just using GPS.
Also I have ventured nearer to airspace than I would before as a result of the GPS.... An excellent tool but I have heard a few stories about guys/girls who use it as their primary source of nav.

[englishal]

As we all know, GPS is far more accurate than anything else out there including QDM, VORs, NDBs, and it is pretty obvious if it does fail in some manner....unlike an NDB unless you're identing it all the time.....As for primary Nav...why not? If you use a proper IFR certified GPS, it'll let you know when it goes tits up.

Cheers
EA

[sharpshot]

I heard from someone who should be a reliable source that you need to allow up to 300m for error. So mind how you go round TMA/CTZ's etc.

Also read your Notams carefully - the "powers that be" carry out GPS jamming trials in some far flung parts of the U.K. Whether or not they are succeeding would be interesting to know - presumably they can do this to stuff the enemy in the event of blighty being attacked :o

[englishal]

Now "selective availability" has been turned off (the code the US government used to mix with the GPS signal to introduce a position error for us non military types), accuracy is down to sub 10m level 99% of the time. They also have the ability to selectively turn off satellites, so for example they can stop GPS working over Israel while it still works perfectly well over the US....You'll probably find this sort of thing happening around major gaterings of heads of state.

One thing...don't trust a "moving map" GPS database to keep you clear of CAS, use the raw position to map your position on a chart. Sometimes errors creep in to the map database.

Mind you, I'd like to see someone navigate with 300m accuracy using only VOR and NDB's

Cheers
EA

[StrateandLevel]

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Having recently acquired a Garmin iii, I wonder how many rely solely on this gadget.
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The first principle of Navigation is that you never rely solely on anything! If you do you will live to regret it one day.

Navigation is the art of colating a variety of information of varying accuracy. Whilst GPS is capable of a very high degree of accuracy, it can disappear and is subject to random errors that the operator is unaware of. Thinking you are precise to 45 metres (not 10) is all very well, but you might be 5 miles displaced with no indication that anything is wrong. Even the rather inaccurate NDB can indicate whether you are N,S,E or W of its position.

If you are flying IFR then you will have a variety of equipment to build a pictiure of your position.

If you are VFR then you should be looking out of the window most of the time, its called "LOOKOUT" You will have a map and should know where you are, if you are unsure, look at the Lat Long on the GPS, place your finger on the map where your GPS says you are and identify the features.

Anyone who relies SOLELY on GPS is an IDIOT

[englishal]

GPS 101

Actually, its nearer 10 m accuracy with a 12 channel receiver. You can have a look athttp://users.erols.com/dlwilson/gpsacc.htm for the results of a series of tests of common GPS receivers. To cut a long story short, the accuracy of the GPS III+ is RMS 4.2m, mean error of 3.6m, within 3.4m 50% of the time, and within 7.5m 95% of the time with an average of 6.8 satellites in view. (A 1° error tracking a VOR at 40 nm will put you 1293m off track as a comparison)

Positional errors are very rare (by this I mean the GPS tells you you're 10 miles from where you should be)...each satellite transmits a health status message, so the receiver will reject error signals. If there are too few satellites in view, then the position error will increase, but your GPS unit will let you know, even the cheap ones like the eTrek.

There's nothing wrong with using GPS as a primary means to Navigation, I've used it to fly IFR in the US. But it IS wise (and good airmanship) to back up you navigation using other methods as well, its called 'situational awareness'.

Anyway, I reckon this post is a wind up

Cheers
EA

[Cat.S]

My Skymap II died on me last week two minutes into a 75 minute return trip from a new destination. Luckily I'd planned my route the old fashioned way too, otherwise......

[Fujiflyer]

I have to admit that I use GPS as my main source of nav info. I use it in conjunction with Jeppesen flightmap. However I constantly monitor it against ground features (if VFR) as well as the normal radio nav aids. I feel the use of it in this way is justified because:

(i) It reduces my workload, particularly in IMC,
(ii) By virtue of the fact I can be more confident of my "exact" position difficult flight scenarios (flying in the Luton / Stansted area springs to mind) are less stressful,
(iii) I can manage without GPS if necessary. I don't always take it with me,
(iv) My setup logs a track file which is very useful when it comes to appraising how well you flew an approach / hold


I tend to be of the view that the more help I can get when I'm flying then the better. My decision to buy the GPS and associated equipment for the map display was made a few years ago when I was doing flights from Rochester to Blackpool early in the morning. The stretch from EGTO LAM BNN wasn't too bad because the VOR's are in the "right places" but I didn't feel confident in the area around Oxford if I couldn't get a service from Brize (parachute zones, HIRTA etc). I do stress though that I always have the VOR etc set up appropriately and prepare a proper flightplan etc. As I said at the beginning I use the GPS as my first choice but am quite happy to do without it if I have to.

[bluskis]

I have been using a Pilot 111 for a few years now, and for route flying I have found it accurate, easy to use after a few flights, and a great help when VOR's are out of range. It is also a great reminder when you stray off your VOR track or heading, even for a few moments.

I find it is not much good at keeping you out of controlled and restricted airspace. This may be a poor data base, or poor depiction of the airspaces, whatever, I don't use it for this purpose.

The other real danger is in inputting user waypoints without verifying the accuracy of your input.

It is a great DME back up and the only one if tracking a VOR without DME facility. I invariably set it on map mode with the DME info on the side bar.
Hope this helps.