Non Precision App Airbus - Overlay Approaches

[Zenj]

Hi,

Can anyone explain please as to requirements for flying with overlay approach but with navaid itself being off, e.g. VOR/DME is off but you do its approach with overlay procedure using the GPS and database in FMGC.

Thanks

[ACMS]

Wouldn't the requirements be the same as a GPS RNAV APP?

Has to be in the FM database
Preferably use FINAL APP mode.

The use of NAV FPA is ok.

GPS primary NAV ACCUR HIGH etc with allowable downgrades on the approach.

[RUMBEAR]

Without checking the FCOM, I think there is a requirement to have local regulatory approval to fly an overlay approach with the ground based navaid unserviceable. The Nav system is certainly capable.

[ACMS]

Yes true, I can't find any info in our books about them at all.

[Goldenrivett]

Hi Zenj,

VOR/DME is off but you do its approach with overlay procedure using the GPS and database in FMGC.

If you are doing a VOR/DME approach, then they must be serviceable else how do you monitor the consistency of the information given by the FMS?
Your OPS manual should specify that the PM should monitor the raw data and call out any discrepancies.

See 7.2 http://www.developpement-durable.gou...NSS__ENGv3.pdf

If the approach is labelled as "VOR/DME or GNSS Approach", then the VOR/DME could be off and you could fly the Approach using GPS and database in FMGC.

The clue is in the title of the Approach Plate.

Hi ACMS,

I'm surprised you can't find anything in your manuals to reflect 4.2.2 of: https://www.casa.gov.au/sites/g/file.../ops/178-1.pdf

" The minima line on the procedure chart is indicated by either:
 the navigation aid that provides the navigation service (NDB, VOR etc.); or
 LNAV or LP for RNAV(GNSS) procedures. Australian charts currently show S-I but are progressively being amended to replace this term with LNAV. The use of the term LP will be dependent upon the introduction of an augmented GNSS service in Australia"

[ACMS]

Don't work for an Aussie company, it's probably in our HKCAD books somewhere? Question is where exactly?

[compressor stall]

I cant speak for other countries, but for Australia you need approval from the regulator for RNP overlay over NDB, VOR approaches.

The main requirement is that the navaid must be still comissioned, just u/s. This would be for obstacle clearance.

[Dan Winterland]

If you have the approval, yes, you can fly them. However, this will vary with aircraft modification states and the approval from the relevant Aviation Authority. In my airline, with FMGC2 (or update equivalent) we can because we have the approval.

If you are doing a VOR/DME approach, then they must be serviceable else how do you monitor the consistency of the information given by the FMS?

Because Performance Based Navigation (PBN) assumes you can fly more accurately if you are in GPS Primary than tracking a radial from a single navaid. It uses an already approved procedure but with far more accuracy. The navaid if not used, is no different from any waypoint on a RNAV approach.

[vilas]

The aircraft equipment is capable of doing it and airbus permits it with approval from authorities.

[Gryphon]

A320 FCOM LIMITATIONS. AUTOFLIGHT. LIM-22-10

USE OF NAV MODE FOR APPROACH

VOR, VOR/DME, NDB or NDB/DME approach procedures may be performed, in NAV, or NAV and FINAL APP mode, provided AP or FD is used, and:

‐ GPS PRIMARY is available. In this case, the reference NAVAID may be unserviceable, or the airborne radio equipment may be inoperative, or not installed, provided operational approval is obtained.
‐ Without GPS PRIMARY:
• The reference NAVAID and the corresponding airborne equipment is serviceable, tuned, and monitored during the approach, or
• The radio NAVAID coverage supports the RNP value, specified for the approach procedure, and an operational approval is obtained

[reynoldsno1]

Because Performance Based Navigation (PBN) assumes you can fly more accurately if you are in GPS Primary than tracking a radial from a single navaid. It uses an already approved procedure but with far more accuracy. The navaid if not used, is no different from any waypoint on a RNAV approach.

A note of caution - by definition any conventional fix is the equivalent of a flyover waypoint, and the obstacle protection areas are designed accordingly. RNAV approach waypoints use a flyby attribute as a default, and the underlying obstacle protection area will not allow for this.

[underfire]

It is just a waypoint, simple as that. It is an overlay, and overlay that uses existing waypoints. Call it the NDB, call it whatever you want, it is simply a waypoint in a database to be used.
You will still assign the procedure define variable such as at or above altitude and/or speed restrictions.

reynolds, no, that is not correct on the definition, a conventional fix is not by definition a flyover waypoint.

In RNP procedure design, we use very, very, very few flyover ways points. The FMS interprets the flyover command in ways you dont want to go through. I dont even use FO on the RW waypoint....

My assistant and I are currently flight validating a new RNP-AR procedure.

[reynoldsno1]

reynolds, no, that is not correct on the definition, a conventional fix is not by definition a flyover waypoint.

I didn't say it was - I said it was the "equivalent". There is no turn anticipation designed into conventional procedures - something that must be appreciated when flying overlay procedures. Nothing whatsoever to do with RNP procedures ...

From an AIP:

Aircraft flying published instrument departure procedures based on
terrestrial navigation aids must fly-over associated NAVAID’s/Fixes unless
otherwise instructed. Operators using FMS to fly these conventional
procedures must ensure the procedures are appropriately coded in their
FMS to achieve this requirement