UK GPS approaches

[ShyTorque]

but allowing GPS approaches but not allowing its use for the missed simply makes no sense to me.

The one reason I can think of is that if an approach was missed because of a failed GPS it would be unwise to carry out the missed approach procedure using the same equipment.

[HeliComparator]

The UK GPS approaches have not been withdrawn. They are still in the UK AIP - but you have to look in the supplements (and realise that you have to click the "view" logo on the right on the supplements page) to find them. The airports with these approaches are Blackpool, Durham TV, Exeter, LGW and LHR. Dunno what happened to Inverness?

HC

[Bravo73]

This is a very recent supplement: (You might need to log into the AIS website to view the pdf)

http://www.ais.org.uk/aes/pubs/aip/p...2008_11_en.PDF

Regarding MAPs, here's an extract (my bold):

11.7 Missed Approach Procedure: To expedite the introduction of RNAV (GNSS) procedures, the Missed Approach Procedures will be conventional, using ground-based navigational aids. These will be reviewed in due course and, after detailed discussions with the airports to determine optimum hold locations and required tracks, will be converted to full RNAV MAPs. Environmental consultation will need to be considered for any new tracks. Until then, all MAPs will be straight ahead to a designated altitude with GNSS track guidance being provided towards the missed approach turning point only. At the designated altitude, or Missed Approach Turning Fix (MATF), whichever is the earlier, the pilot should revert to conventional navigation and route to the holding beacon, ie by making a turn to the beacon or a turn with continued climb to holding altitude at the beacon.

.
.
.
And here's the 'original' supplement from Nov '07:

http://www.ais.org.uk/aes/pubs/aip/p...2007_34_en.PDF

Time for a quick u-turn, NavMonkey?

[SASless]

Shy,

If I use a VOR/DME approach....normally the Missed Approach usually has me trodding off for a hold at the VOR, some intersection, or a radial and DME distance.

Now how does that differ from GPS?

In your view I take it you differentiate between NDB's, VOR's and GPS for some reason. Are they not all the same concept....navigation using some sort of electronic means?

If we lowly country bumpkins can overlay a GPS approach on a VOR or NDB approach including the missed approach.....why not the UK?

I will bet you a donut to a dog dropping....you can hold the stakes in your mouth....and I will wager that a GPS approach without WAAS is still much more accurate than the VOR approach and for much...much...more accurate than any NDB approach.

[Gomer Pylot]

A GPS approach without WAAS is actually more accurate than an ILS, at least horizontally. A GPS fix without WAAS is, IIRC, accurate to 10 meters. and you get that all the way from the IAF to the MAP. WAAS doesn't help a lot with horizontal accuracy, it was implemented to get vertical accuracy good enough for use with precision approaches, giving a glideslope.

Like it or not, the current navaid system is going to go away, because it's simply not economically viable. The maintenance costs on aging analog systems, using vacuum tubes in many cases, are just too high to be kept up. We're no longer flying range approaches, and I predict we won't be flying NDB or VOR approaches that much longer. Technology advances, and we have to give up obsolescent parts of it.

[NavMonkey]

Hi Bravo,

You had me worried for a moment

The 2007 supplement you quote states that:

Currently six licensed aerodromes, as listed below, have approved designs for RNAV (GNSS) instrument approach procedures.
Notification of operational availability of these procedures will be through NOTAM action by the specified aerodrome.
Blackpool
Durham Tees Valley
Exeter
Gloucestershire
London Gatwick
London Heathrow

Note that the CAA are talking about "approved designs" for the procedure, not the availability of the approach to be flown. Also see the comment about NOTAM and the lack of mention of some of the former trial airfields e.g. Inverness.

If you had looked a little further through the 2008 supp you quoted you would see that on one hand is says that the NATS RNAV GNSS approaches at EGLL and EGKK will commence from 5 June 08, on the other it states that

Notification of operational availability of the procedures at Blackpool, Durham Tees Valley, Exeter and
Gloucestershire will be through NOTAM action by the specifed aerodrome.

Looking at the current NOTAMS we get:

Blackpool RNAV APPROACHES NOT AVBL
Durham RWY 05/23 GNSS APPROACH NOT AVBL
Gloucestershire RNAV (GNSS) APPROACHES NOT AVBL
Exeter TRIGGER NOTAM on 5th June UK RNAV (GNSS) INSTRUMENT APPROACH PROCEDURES, SUP S11/2008 REFERS

Still looks to me like nothing is available. Whilst the IAP may be available and in your databases it still doesn't mean that its available to be flown until the airports comply with the

Notice to Aerodrome Licence
Holders (NOTAL) 4/2007 specifying the responsibilities and actions required of licence holders intending to introduce RNAV (GNSS)
approach operations.

More than happy to be corrected if my reading of the situation is wrong though... also good news that we will have RNAV GNSS approaches in the UK from 5th June too

Cheers, Nav.

[HeliComparator]

Gomer sorry but I can't agree with your comment that non-WAAS gps is more accurate than ILS, nor that its error is 10m. The whole problem with gps is that there is no maximum error. You could say "the error is no more than 10m for 99% of the time" but what about the 1% or even 0.1% when the error is 100m or more. The maximum error for 0.001% of the time is perhaps 1000m (making these figures up but you hopefully get my gist). GPS near the ground can be further degraded by multipath reception from buildings etc. So outside of 99% of the time, WAAS makes a big difference horizontally.

RAIM gives a certain degree of protection but for a tso129 receiver the best it can do is to tell you that there is a RAIM problem and the best you can do is to discontinue the approach - not very good if you are already at your alternate on minimum fuel with no other approach aids.

FDE RAIM for tso145/6 receivers deals more gracefully with RAIM problems by deselecting the faulty satellite and, if you still have enough satellites, you can continue the approach.

ILS of course has the advantage that it gets more accurate the nearer to the ground you get. Yes ILSs can fail too but its a so much simpler and more robust system than gps that the probability is remote.

HC

[212man]

FDE RAIM for tso145/6 receivers deals more gracefully with RAIM problems by deselecting the faulty satellite and, if you still have enough satellites, you can continue the approach.

Surely all RAIM kit does that? You need 4 SVs to get a 3-d position and 5 SVs to provide RAIM. More than 5 SVs gives you redundancy to maintain RAIM while deselecting SVs. If you start with 5 and then deselect one, you no longer have RAIM and will therefore have to discontinue the approach, no?

[ShyTorque]

In your view I take it you differentiate between NDB's, VOR's and GPS for some reason. Are they not all the same concept....navigation using some sort of electronic means?

SASless,

But I didn't say it was my view, nor that I agreed with it. It's the view of the CAA.

I use GPS and VOR/DME/NDBs routinely, every working day. Two GPSs, in fact, plus a nice moving map, also driven by GPS.

I use one GPS to back up the other and the other radio navaids to confirm that what I'm seeing is correct, in one contiguous package.

And I look out of the window a lot, too.

In my view, GPS is the best thing that's happened to aviation in decades.

[HeliComparator]

212 - no, I don't think "ordinary" RAIM identifies the faulty satellite - it just says there is a problem. Type RAIM into wikipedia and see if you agree with my interpretation. Its true that many GPSs allow you to deselect satellites but that is no good if you don't know which one to turn off.

CAA Spec 22 that we know and love, says that in the event of the RAIM alarm limit being exceeded, you have to navigate by other means (and that is just when using for en-route!)

FDE RAIM does it all automatically (that's part of the tso145/6 spec) and if you have WAAS (SBAS) then FDE RAIM is not really necessary because the SBAS signal tells your receiver to ignore dodgy satellites - even if it doesn't have enough for FDE RAIM

HC