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

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

Satellite 30? It'll be some system that doesn't report it as U/S. Galilleo isn't a reality yet

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 Well, they are not quite empty words, because they will make GPS approach legality dependent on paying for the "higher integrity" signal

giloc

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

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".
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.