RNP/VNAV/APV contingencies.
 

:hmm:Dear all,

It seems that some operators may not provide sufficient guidance concerning RNP approach contingencies.

It would be in many interests if you could share your airline info on that matter.

1)Preflight requirements.

2)Contingencies procedures before and after the FAF.

Thank you!

First of all I would like suggest to have RAIM checks included in TEXT format (not the low quality 3-day spread graphic option) by default in TAF for next H24.

Then airline/aircraft designs differ somewhat to note all variations of briefing and requirements, unless the topic is adjusted for this, even each aircraft type has variations based on installations on board...

If IMC after the FAF and an "UNABLE RNP" message appears, GO AROUND!

We get RAIM notices in text format. They usually appear in the NOTAM section of the airport.

AFM Sup for RNP ops.
It's going to be different for aircraft types.

Thanks.
Unable RNP,or "unable required nav perf" and other fmc sratchpad messages such,"FMC disagree" are clear cut mandatory go arounds.

.How about A/P failure or F/D failure before or after the FAF?
The 737 allows AP off with FD ON or AP ON with FD OFF.
Does you airline allow such configuration before the FAF? or only to continue after having passed the FAF?

.Prior to a GNSS approach,a loss of GPS receivers(GPS light in 737) before the FAF,for example 20 NM..while the ANP remains in the RNP,does your airline allow you continue beyond the FAF?

Dear FE Hoppy,

Yes indeed,the AFM provides some guidance of what the aircraft is able to do,however contingencies are not laid down.
The 737 NG would be the main type for this discussion but if other types provide info valid for others then why not.

RNP (AR) operation is only allowed in LNAV/VNAV in my outfit, therefore yes, you need either the autopilot or the flight director. All other approaches can be flown using IAN and therefore neither AP nor FD is needed. After the FAF one can continue after a failure only, if sufficient visual reference is established and can be maintained.

And yes, if the ANP remains below the RNP we can continue, even for a dual GPS loss on a GNSS approach.

Thanks denti,

So your airline is clear,any failure after the FAF would mean a go around unless in viusal conditions.
Failure such as? Du failure?

Are we talking about the fact that a failure requiring a NNC should be done before the FAF?
How about lnav/vnav disconnnect in imc..during a LOC approach ,does your airline allow you to continue with vorloc mode and v/s as long as you are in raw data limits?

No, it was probably poorly worded on my part. Total loss of AP/FD would be a reason for a go-around as RNP approaches have to be flown in LNAV/VNAV and that only available with either FD or AP working and engaged. As of course would be the usual ND/scratchpad messages (UNABLE RNP/VNP etc). DU failures are not mentioned and as the required information is still available they are not a reason for a go around. NNCs have to be completed by 1000ft, same as any other checklists.

LOC approaches are flown in IAN and therefore approach mode (which uses LOC and GP). However VORLOC/VNAV is a valid backup mode and VORLOC/VS is a secondary backup mode. So yes, if you are done with every required procedure by 1000ft, sure you can continue. Although it might be a better idea to go around and set up for second approach using the basic modes.

Understand and agree.

[QUOTE]And yes, if the ANP remains below the RNP we can continue, even for a dual GPS loss on a GNSS approach.[QUOTE]

IIRC 738 with dual GPS receiver failure, you'll get a TERRAIN POS (or some verbiage to that effect) alert on the ND long before the ANP exceeds RNP. You're left with the magenta line (INS & DME/DME referenced) but the Terrain Display is removed (both from the ND & VSD) and I believe some EGPWS functions are degraded. With ANP gradually increasing but still less than RNP, do you continue under these circumstances?

Also IIRC 738 IAN can be used on an RNP (AR) approach as long as there are no RF turns involved. Many US RNP (AR) approaches have numerous transitions to a FAF on straight-in final approach, some of the transitions with RF turns (LNAV/VNAV req'd), but some with straight-in transitions (no RFs, IAN acceptable AFAIK).

Interesting point about IAN and RNP. Yes, the explanation to us was that the approach mode is (currently) only able and certified for straight in approaches, so it can't do curved GLS approaches or RF legs on RNP/RNAV approaches. There are not all that many RNP (AR) approaches in europe yet, the ones we used (LOWI and LOWS mainly) had RF legs and therefore the one size fits all approach in not approving IAN for RNP (AR) was probable the easiest way.

Quite honestly, never had a dual GPS failure at all, and even the single GPS failures were only for a few seconds at most. So i have absolutely no experience when the terrain display will disappear. Of course it would be a judgement call if one continues or not, especially if there is a longwinded low RNP missed approach at the end of the approach it probably would be better to discontinue earlier than later to get out of the terrain.

.Boeing 737 NG QRH says continue.

The GPWS mode gets info from the GPS but also ADIRS and RA for the terrain clearance floor .
The Terrain clearance floor (TCF) will use FMC position if the GPS fails and will give alerts if the aircraft descends below that floor.
For terrain ahead,if the GPS was out more than 15 minutes,the enhanced modes should not be deemed reliable and TERR INHIBIT should be set to the override position.

.FCTM says 1 GPS required to conduct an RNP approach.

Dispatch requirement?certainly,before FAF requirement as well?
I believe to pass the FAF,1 GPS must be serviceable,after that a pilot decision indeed.

Our FCOM has a SP detailing the pre-approach requirements for RNP AR, incl. 2 GPS receivers, 2 PFD/ND (ref: the other thread) and lots of other things.

No similar list for 'other' RNP approaches, e.g. to LNAV minima.

For the B737NG.
Very broadly speaking, and assuming the crew, aeroplane, airfield are approved, and the procedure is in the FMC.

Before we commence an RNP/RNAV STAR we need one of everything to be working.
For an RNP approach using LNAV only, one of everything
For an RNP approach using LNAV and VNAV, in addition to having one of everything, we need 2xADIRUs in NAV and 2xPFDs
For an RNP AR approach, down to a DA(H) we need two of everything, (except the EGPWS and Autopilot). We fly these as RF (curved approaches).

Again very broadly speaking we should carry out a missed approach if..
After the IAF, and in IMC, any message that indicates uncertainty of position, when unable to engage/reengage LNAV, or LNAV/VNAV, if the approach is an LNAV/VNAV AR approach a DUAL RA failure.
After the FAF, using VNAV then we must carry out a missed approach if we have a continuous Vertical Deviation Alert.

Our manuals are more detailed but that's the gist of it.

ok465:

The convention for RF on RNP AR IAPs in the U.S. is to have a procedural note in the briefing strap that states "RF required" if it RF is required for all the transitions, or the final segment, or the missed approach. But, if RF is not required for the final segment or the missed approach, but only for some of the transitions, then "RE Required" will be annotated in the plan view to the beginning of that transition(s).

Unfortunately, this convention is not uniform through the rest of the world.