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Does Anyone in the UK Get Vertical Guidance from their GTN650/750?

Hi,

I’m new to the forum but I’ve been having a few days worth of brain scratching and my only option is to come and beg for help.

I am flying a club PA28 with a GTN650 with the aim of shooting some practice RNAV approaches, specifically using the vertical guidance that the GTN650 offers. The GTN has v6.51 software, however the database hasn’t been updated since Feb-18.

Unfortunately, when loading up either of the RNAV approaches into Cambridge (EGSC), only LNAV is offered, rather than LNAV/VNAV or even LNAV+V. I would have thought at least LNAV/VNAV would be an option given that it is listed on the approach plates.

I initially had a feeling that the GTN may be downgrading the approaches to LNAV, so I looked at other airports around the UK and Europe within the PROC pages to compare. I noticed that UK airports seem to only offer LNAV unless it specifially has LPV minima available (in places such as Exeter), in which case it offered LPV guidance. Whilst looking in Europe, (I checked EDDF and EDFH) both offer me LNAV+V and LNAV/VNAV approaches.

I am therefore drawing a conclusion that rather than the GTN downgrading the approaches to just LNAV due to GPS/WAAS issues, it must be a UK specific thing that LNAV/VNAV or LNAV+V can’t be used as these options show up in other parts of Europe?

Hence why I pose the question “Does Anyone in the UK Get Vertical Guidance from their GTN650/750?”…

I have already seen some great information on this forum regarding this topic, especially this page of posts, however it wasn’t a UK based user. I have checked everything on the GTN650 to make sure WAAS is enabled. I have also tried to install the v6.50 GTN PC trainer to check what that thinks, however that doesn’t work on my computer and only loads a blank 750 unit which won’t turn on.

Peter, I have seen many of your posts which are extremely helpful and have already got me very far into understanding this subject, so thank you. I’m just looking for a little more clarity as to whether the GTN is setup incorrectly, or whether RNAV approaches in the UK with LNAV or LNAV/VNAV minima have been deliberately (or otherwise) coded into the database to not offer vertical guidance.

Last Edited by TonesTaxis at 07 Dec 15:38
United Kingdom

The problem, often aired before, is that the VNAV element of LNAV/VNAV is switched off in the UK by order of the CAA.

If you go to other places in the UK, eg Cranfield, Gloucester which have LNAV approaches, you’ll almost certainly get LNAV+V, and if you go to Alderney you’ll get LPV. If you go to somewhere in France with LNAV/VNAV, you’ll also get a slope.

This is all down to typical CAA arse-covering, where they promote a tiny issue (the possibility that SBAS VNAV may not exactly match Baro-VNAV) above the much bigger issue of turning a 3D approach into a 2D one.

May I recommend the PBN Manual, where this is all explained?

EGKB Biggin Hill

Presumably, if you go somewhere with NO instrument approach it will give you a 3 degree path to the runway much like the Proline21 “visual” approach which means the autopilot will fly an ILS like approach into any airfield in the database.

If that is the case the problem exists only for LNAV/VNAV approaches, am I right?

Darley Moor, Gamston (UK)

Cardiff also offers LPV.

Oxford (EGTK), United Kingdom

Neil wrote:

Presumably, if you go somewhere with NO instrument approach it will give you a 3 degree path to the runway much like the Proline21 “visual” approach which means the autopilot will fly an ILS like approach into any airfield in the database.

If that is the case the problem exists only for LNAV/VNAV approaches, am I right?

I wouldn’t put it like that. “Visual” approaches, are available for all AIP runway ends in GTN v6.41 and later, regardless of whether they have instrument approaches or not.

So you can fly the Cambridge Visual Approach, which is effectively an LPV, instead of the LNAV/VNAV (which, because of CAA action, is just an LNAV approach.)

But it wouldn’t be an approved approach, and you wouldn’t get fed into it from the procedural RNP approach.

So, if you wanted, and were a bit of a maverick, you would have to load the standard RNP approach, then, somewhere near the IF, quickly change to the Visual Approach and get what is, to all intents and purposes, a full LPV approach. But you would still be limited to LNAV minima, of course.

The rights and wrongs of doing this are really complex, and demonstrate just how removed from technological reality the regulators now are. This is not like using a VOR to fly an ILS approach. The SIS and the software are exactly the same for the Visual Approach as they would be for an LPV, and the area (at least in the 23 case) has been surveyed for an ILS approach, so it would be perfectly reasonable to fly the Visual Approach in IMC to LPV minima.

The same is not true, of course, flying a Visual Approach in IMC to a VFR runway, though that option is also (quite legally) available, but with no minima.

It’s a bloody mess and it’s time the regulators caught up, but that ain’t going to happen while they are desperately under-resourced, often under-educated and spending a lot of their efforts planning to plug the gaps left by our incompetent government.

EGKB Biggin Hill

Sorry, SIS = Signal in Space (the GNSS signal).

The situation is really complicated and my previous post didn’t give all the factors to consider by a large margin. I could say much more, but it could get really boring.

EGKB Biggin Hill

If that is the case the problem exists only for LNAV/VNAV approaches, am I right?

I am not up to date on this but it has been years since it was discovered that LNAV with “baro VNAV” were suppressed for some airports in the UK, in the Jepp databases.

A search for
baro AND vnav
digs out various threads e.g. this. As usual, loads of past discussions, awaiting you

It didn’t affect most GA GPS installations because most can’t do baro VNAV.

Welcome to EuroGA, TonesTaxis

Administrator
Shoreham EGKA, United Kingdom

It didn’t affect most GA GPS installations because most can’t do baro VNAV.

Nope. That is a misunderstanding. It did affect GNSS installations, because SBAS is supposed to substitute for Baro-VNAV, and does everywhere else, but the CAA’s infinite wisdom (greater than any other authority) meant that SBAS VNAV was switched off in the UK.

EGKB Biggin Hill

Actually Timothy I find it very interesting

So you can fly the Cambridge Visual Approach, which is effectively an LPV,

The data block for a true LPV is very different than the pseudo GS of a visual approach vertical guidance, is it not?

Oxford (EGTK), United Kingdom
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