How do we fly VOR approaches in jet aircraft?

[Dr.Pilot]

Hola guys!

I've been recently asked if we need to monitor RNP value during VOR approach using FMS as the main navigation source.

So, personally I think we DO NOT have to monitor our RNP vs. ANP/EPU, instead we have to monitor our approach via basic needles (+-5 degrees) - the same as if it would be flown in C172.

But my colleagues believe that because we use LNAV/VNAV functions for VOR approach it is considered as RNP, so RNP 0.3 required.

What do you think?

[wiggy]

Well...used to be that if you were flying a published VOR procedure then the manuals very clearly stated "needles" took primacy and the fact you had LNAV was just a nice to have...nowadays with all the verbiage surrounding PBN I'm less inclined to be definitive without diving into the FCTM..

Then again I'll offer that my first response if asked that sort of question would be, "OK, lets be pragmatic, for example:

You are flying a VOR/DME with no RNP alerting requirement, and you get "Nav Unable RNP" .. the QRH may well will lead you to "verify position" - well to do that, lets look at the VOR/DME...


I

[rudestuff]

You're referencing the needles. The LNAV/VNAV is only guiding the airplane, no different than if you were hand flying it.

[parkfell]

Where is the harm having the VOR (needles) and DME ticking away in the background when flying say a LNAV/ VNAV approach or equivalent.....?

[blind pew]

Have standards dropped so low and blind reliance on automatics become de rigueur that professionals do not use all available information to ensure the safety of their flight that they need regulations to cover their ar$es?

[deltahotel]

Our SOP is to use LNAV/VNAV for non RNP approaches, monitor the raw data (needles and range vs height) and intervene if necessary. Seems reasonable to me.

As an aside CAA Doc 24 detailed testing standards for LST or LPC require 2D approaches to be flown using manually selected vertical guidance (FPA or VS).

[wiggy]

Obviously, if a RNP alert pops up, in IMC, during the final approach segment, I’m not sure if I would be confident to “trust the needles” as they are within 5 degrees...

TBH I’m not sure I understand the logic with that. If you don’t trust (but verify etc) the needles how do/ did we ever fly VOR approaches?

[champair79]

This all forms part of the brief and downgrade options. Ultimately you are flying using the needles but you may be using the green/magenta string to fly it in FINAL APP/ LNAV/VNAV. Our ops manual on the Airbus for example says we need GPS PRIMARY for FINAL APP and NAV-FPA. If we lose that (even if predicted nav accuracy is still high), we have to revert to TRK FPA (i.e. basic needle flying).

You need to pre-brief what you're going to do in the unlikely event your nav capability downgrades. What if the navaid is badly calibrated? What if it's a CAVOK day? What sort of terrain is nearby? Some is prescribed, some is airmanship.

Champ