A320 Radio Nav disable

[MD83FO]

Hello, are we required to disable RADIO NAV update on an RNP GNSS ONLY IAP?

thanks.

[tubby linton]

This is not a requirement in my airline, and it is not mentioned in the pdp for GNSS provided by Airbus.

[Amadis of Gaul]

We don't have such a requirement either.

[vilas]

It is a requirement for RNP AR.

[EMIT]

O(riginal) P(oster), do you mean that for an approach, where GPS is a requirement, you think that you should disable DME/DME updates, in order to be legal?

Isn't the priority sequence for updating, first GPS position, then DM/DME position, then VOR/DME position, which last mentined mode could be fighting for priotity with raw average INS position depending on time in NAV mode?

If GPS is available, IT will be the primary position source, so it wil not be necessary to DISABLE DME/DME updates. If DME/DME updating happens to be the primary mode, it means that GPS is not available, and if that is the case, a GPS REQUIRED approach cannot legally be performed.

Don't start your reasoning process from the back-end of the solution.

[I-2021]

As per Vilas. You can find the reason in the GTG with RNP AR.

[tubby linton]

Would you please provide a link to GTG with RNP AR. My airline requires a RAIM prediction before departure if a crew can expect to fly a gnss approach.
How are you disabling Radio Nav updating?

[vilas]

Tubby
DATA__POSITION MONITOR _DESELECT NAV and
Check predictive GPS on progress page for GPS Primary at ETA.

[tubby linton]

Not all fmgs have the predictive GPS page and this requires a crew to access a RAIM forecasting website AUGUR GPS RAIM Prediction Tool - GPS Status (http://augur.ecacnav.com/)

[divinehover]

For RNP-AR only. It's meant to protect the Nav accuracy (in case of corrupt ground station signal) in the case of GPS Primary failure to allow for a safe extraction procedure on IRS Nav. Nav accuracy should remain HIGH until a safe extraction in completed. A corrupt ground based signal will worsen the Nav accuracy.

[MD83FO]

It is required for RNP AR. but the GNSS ONLY note on RNAV IAP has people thinking as our PBN manual does not specify.

[tubby linton]

Have a look at this FAA AC and in particular appendix 2.
http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%2090-101A.pdf

I think that your procedure only applies to RNP AR, as the normal requirement for a standard go around is an accuracy of 1.0 nm.

I would still like to know what GTG is.

[vilas]

tubby
Getting to grips with RNP AR by Airbus. Check it on smart cockpit.

[vilas]

MD83FO
If you see the following page in FCOM it asks you to deselect NAV aids.
APPROACH USING FINAL APP GUIDANCE FOR RNAV(RNP)
PRO-NOR-SOP-18-C P 7/20


FCOM ← C → 11 DEC 13

[tubby linton]

Thank you Vilas.

[jmd2k]

For RNP-AR only. It's meant to protect the Nav accuracy (in case of corrupt ground station signal) in the case of GPS Primary failure to allow for a safe extraction procedure on IRS Nav. Nav accuracy should remain HIGH until a safe extraction in completed. A corrupt ground based signal will worsen the Nav accuracy.

Great explanation, I could not be more precise.