PRNAV with navaid U/S
 

Hi , if you are PRNAV equipped and given a SID based on a VOR that is U/S can you accept it?
Thanks

No.

Rnav is Rnav. If the departure specifies radials from an aid, that aid must be available as a reference.

Check regs any part (equipmet) of a apr or dep proc that is not available makes that procedure unusable

Err... not quite. B-RNAV and P-RNAV departures differ in that B-RNAV would require a turn below MSA to be based on a navaid. Not so for P-RNAV, where turns to waypoints can be initiated below MSA, once above 400'. There might be a navaid that is part of a P-RNAV departure, but that's most probably because it's an overlay of an existing B-RNAV SID. It doesn't matter if it's U/S: the only thing you need is the navigation accuracy (1.0 or less) required for P-RNAV, the aircraft has no defect make you P-RNAV unable and the crew has received P-RNAV training. As far as the flight management system is concerned, the U/S navaid is just another waypoint.

P

homerj, PRNAV is based on the aircraft's ability to maintain the required accuracy. It can be done using VOR/DME, GNSS, GPS whatever is available and functioning properly. In other words as long as you have GPS primary displayed it's a go unless specific requirement for VOR/DME being serviceable is stipulated either by the chart or notam. :ok:

Ok , im confused.

There are places with sids based on conventional navaids that have Rnav overlays.So in such a case if a navaid was U/S you can go.But in a case where you are given a sid , based on a VOR with no RNAV overlay and the VOR is U/S can you go.I understand its no problem for the FMC but is it legal???

Hi Homerj,

The way I understand it is :- that particular SID won't be available whilst the Nav aid is US - so a different clearance will be issued. Lots of Airports have additional RNAV / PRNAV SIDs (which basically fly the same procedure), so those aircraft so equipped will have no problem.

In the old days, before RNAV, - ATC would amend the SID by stating a radar heading or another radio aid / radial etc. to navigate by.

Homerj,

Read my post again. You asked about PRNAV departures, which DO NOT require specific navaids to be serviceable since they rely on the FMC accuracy to be sufficient to fly the correct track.

If the SID is an RNAV overlay (BRNAV unless is clearly specifies PRNAV), you cannot use that SID if the the U/S navaid is required to follow the SID track BELOW MSA.

If the SID is an RNAV overlay and the U/S navaid is used to define the track once ABOVE MSA, you can go because BRNAV accuracy (based on FMC position) is sufficient once you are clear of terrain.

I think you are confusing RNAV overlays and PRNAV departures.

P

Would one be able to collect a departure clearance for a SID based on a defunct navaid?

homerj, methinks you need to get somewhat clearer picture bout RNAV procedures. As said before I can think only of one case (apart from the reasons mentioned before) one wouldn't be able to fly PRNAV SID namely if the PRNAV approval was obtained based on VOR/DME accuracy update method. That's certainly not the case with a modern jetliner having GPS installed. :ok:

In theory no, but I wouldn't put it past Cagliari ATC :}

P

homerj, the answer to your Q (in Europe) is ...

If the route (SID) is designated 'P-RNAV' then the availability or otherwise of any VOR is irrelevant. VOR is not a valid P-RNAV sensor. Your RNAV system may use VOR information (as well as GNSS and DME, and INS perhaps) but it is not a REQUIRED sensor for P-RNAV navigation.

Routes that do include VOR/DME radial/distance info are probably designed to B-RNAV standards - this is allowed in any event above MSA, and below MSA is allowed where terrain/obstacle considerations permit use of B-RNAV criteria. So if the chart does not specify 'P-RNAV' or RNP-1, then B-RNAV compliant equipment may be used unless your equipment relies on that inop VOR.

But you need the RNP/ANP feature correctly set at 1