A320 VOR approach

[Willy Miller]

So you are flying a fully managed VOR approach and the cleaner at the airport unplugs the VOR transmitter (or you pull the VOR1/2 CBs for some reason).

What will happen?

Will the a/c continue with its programmed "overlay approach"

Thank you in advance

[underfire]

I guess as soon as you see FINAL APP, you have the NAV and VNAV solution in the box....

[safelife]

It will continue like nothing happened, because the NAV mode as no connection, at all, to the VOR receivers.

[aterpster]

Under FAA rules you cannot continue the final segment without the VOR raw data.

[Lookleft]

The question should really be what should the crew be doing? If the VOR is no longer working then the ident on the ND won't be displayed. You no longer have raw data and you should be going around.

[akindofmagic]

Which is correct but somewhat anachronistic considering the reliability and accuracy of GNSS navigation, which is what the aeroplane is using to navigate and follow the overlay (assuming GPS installed of course).

[aterpster]

When VOR approaches were also "...or GPS" the final approach sensitivity, accuracy, and alerting went to approach mode (RNP 0.30). Without overlay LNAV remains in terminal mode, which is insufficient for the final approach segment.

[galaxy flyer]

Now that, aterpster, is an interstinf fact I'd never been told. At one time the schoolhouse taught fly the FMS as an overlay, don't be concerned with the VOR raw data. Then, RC changed the FMS LNAV database on VOR and NDB approaches to note "for reference approach only" meaning raw data required. Now, I know why.

[Capt Scribble]

You continue because the approach is not being flown wrt the VOR beacon, it is merely the nav system following the VOR track as shown on the plate and kept accurate by GPS. You have no monitoring but neither can you monitor a GNSS approach except by the system maintaining the correct RNP. Its in the FCOM.

[aterpster]

I can only speak to FAA policy. The final segment of a VOR approach must use VOR raw data. In terminal sensitivity LNAV is not VOR raw data.

Having said that, if any given commercial operator can get ops specs approval to use LNAV in terminal mode (RNP 1.0) in lieu of VOR raw data, then an exception has been granted, right or wrong.

We all know that LNAV in the terminal mode will likely do a better job of flying the final approach segment than tracking raw VOR, but the integrity and alerting will be lacking. And, that will probably never matter.

How many VOR approaches are flown these days anyway?

[Denti]

Dunno about others, but on our A320s the VOR approaches are coded in RNP 0.3 and the aircraft automatically switches to that, was the same on the 737 as well. As VOR is often one of the back up approaches for an ILS here they are certainly flown on a semi-regular basis.

[Dan Winterland]

How many VOR approaches are flown these days anyway?

Quite a few in some parts of the world. The question I have to ask is that if flying a fully managed approach and the navaid in question did stop transmitting, how many pilots would notice?

[fab777]

Those who do their job...

[aterpster]

Originally Posted by Denti

Dunno about others, but on our A320s the VOR approaches are coded in RNP 0.3 and the aircraft automatically switches to that, was the same on the 737 as well. As VOR is often one of the back up approaches for an ILS here they are certainly flown on a semi-regular basis.

Is your database supplier Jeppesen or LIDO? Jeppesen doesn't code VOR approaches for LNAV RNP 0.30 for their public database. (unless they are overlay; i.e., "...or GPS.) Perhaps they do for a tailored airline database.

[Denti]

As far as i know LIDO, well, we do use their flight planning system, charts, engine out procedures and i guess their FMC databases as well. However, with Jepp they did code it the same way for us. Might be tailored, or just a difference between europe and the US. Heck, even in the old non-gps classics it was coded in 0.3, same as any other NPA. But back then we certainly bought tailored stuff from Jeppesen, their airport booklets (one small book with all charts in the correct order per airport) were great, much better than those chart binders our colleagues at other airlines used.

[aterpster]

I flew the early 767 1984 through mid 1986. The pre-GPS FMS was like a Radio Shack toy computer. When we had to fly a VOR approach the approach was in the database. The PF used the database approach because tracking was smooth whereas the VOR was awful. The company required the PNF to monitor raw data, which was easy in the 767. We didn't know what RNP 0.30 was in those days.

[akindofmagic]

That's the aircraft limitation. The relevant authority may have a different view.

[aterpster]

Originally Posted by IBE8720

For the people who want to argue and say, What if you don't have GPS Primary.
The next line says, if you don't have GPS Primary, then you need the NAVAID for Raw Data.

Well, they have it half right.

[compressor stall]

Same, although for us it's limited to my own country's airspace.