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Garmin +V Advisory Glidepath

Doing some training at Gloucester today for an IR(R) holder with GTN650 equipped PA28, I am wondering:

I think the +V is set according to the published slope hence it picks up the 3.5 degree required, but is there any way on the unit of confirming what the +V slope is set at for a particular approach?

What is the thinking on disabling the +V for training – should we? How? Etc..

Grateful of thoughts thank you

FI - FE - FICI
Oxfordshire / Glocs

There is some confusion around switching off GP on the GTN at the moment. It seems that with the latest software under most circumstances you get a GP even with SBAS switched off.

No-one has definitively discovered the rules of when you do and when you don’t. Another project for my copious free time.

EGKB Biggin Hill

Most IR examiners do not disable equipment features, and I believe this is official ‘unwritten?’ policy. Some will cover the vertical guidance with a home made cad to simulate a ‘true’ 2D approach, while others are OK with the candidate flying a CDFA and calling out crossing altitudes, with appropriate corrections.

Disabling equipment opens a can of worms. Not the same as simulating OEI.

Enstone (EGTN), Oxford (EGTK)

you get a GP even with SBAS switched off.

That is of course technically possible (non-EGNOS GPS is plenty accurate enough for a “practical job”) but would be pretty amazing.

Administrator
Shoreham EGKA, United Kingdom

That is of course technically possible (non-EGNOS GPS is plenty accurate enough for a “practical job”) but would be pretty amazing.

It has been suggested that it only works if you have barometric input to the GTN, but I feel that I have seen it on units without.

Or maybe barometric input is more common than I realised.

EGKB Biggin Hill

Or maybe barometric input is more common than I realised.

I can believe pressure altitude is very common, via Garmin transponders’ connection to the GTN. Barometric setting on the other hand… Maybe you spend most of your time on posh planes these days

EGTF, LFTF

Baro input is normally installed on IFR GPSs, in the form of the 10 gray code wires being brought in (not the static pipe itself). With RAIM, it allows a RAIM check to pass with 1 less satellite. Lots of old threads here.

But as denopa said the GPS doesn’t know the QNH so this would not be useful. In GA, the QNH knob of an encoding altimeter is a 10 turn pot which outputs a voltage; no IFR GPS I know of has an input for that, and it would have no use for it. OTOH, how exactly is BARO-VNAV implemented unless the box knows the QNH?

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

how exactly is BARO-VNAV implemented unless the box knows the QNH?

Well, we know it works, right? And we know that GPS without SBAS is barely up to the job (which is why 129 receivers don’t do glidepaths) so there must be an algorithm in there. I’ll try to investigate.

EGKB Biggin Hill

Peter wrote:

Baro input is normally installed on IFR GPSs, in the form of the 10 gray code wires being brought in (not the static pipe itself). With RAIM, it allows a RAIM check to pass with 1 less satellite. Lots of old threads here.
But as denopa said the GPS doesn’t know the QNH so this would not be useful. In GA, the QNH knob of an encoding altimeter is a 10 turn pot which outputs a voltage; no IFR GPS I know of has an input for that, and it would have no use for it. OTOH, how exactly is BARO-VNAV implemented unless the box knows the QNH?

In the Proline 21 “visual” approach it needs you to have set QNH correctly, so it definitely uses that info.

Darley Moor, Gamston (UK)

That is quite an integrated system though.

Which GA navigators (GTN/IFD) do BARO-VNAV and offer +V or LPV? I can look in the IM to see if there is a connection for the QNH pot.

Administrator
Shoreham EGKA, United Kingdom
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