FAP on RNP approaches
 

Hi all,

Does anyone know why on RNP approaches, the final approach segment begins with a FAP, as opposed to a FAF on "conventional" RNAV approaches?

I think...

ICAO:

• RNAV / GNSS (RNP APCH) approaches may be flown as a Non-Precision Approach (e.g., LNAV only) with no vertical guidance, hence the final approach start is indicated as a FAF like on any other NPA
• RNP AR APCH final approaches requires vertical guidance (APV) -- by definition -- hence the beginning of the final segment is indicated as a FAP

FAA:

• We don't care... both are FAFs

Thanks. I take your point on APV- we've got a ton of them here in the US- usually as LPV approaches. However, even the FAA RNP approaches show "FAP", so they don't really consider them fixes, as you've suggested.

Going back to your point on the vertical guidance though, isn't the start of the final segment a defined lat/long point anyway? Why not just call it a FAF instead of FAP?

Here are excerpts from three FAA RNP approaches, with the start of their final segments charted as "FAF":

http://i.imgur.com/l5HlNB3.png

Yes I believe that's what the FAA does (per the above examples).

Technically a FAP isn't defined as only lat/long (2D) but it is a 3D position with an altitude as well. The FAP is the intersection between the final approach path and the intermediate segment altitude.

And operationally the FAP is where the glideslope is intercepted, which geographically may shift a little bit depending on the actual altitude flown.

FAF is for non-precision instrument approach, FAP is for precision instrument approach.

the FAA calls RNP non-precision.

Nope, both FAA and ICAO call them APV approaches. Hence they are flown to a DA(H). A Non-Precision Approach would be flown to an MDA & MAP instead.

Thanks. I understand the concept of a FAP on an ILS, but on any RNAV procedure, the point will always be referenced by a lat and long, correct, so why not FAF? It doesn't really affect the way we fly the approach. More of a curiosity really.

Thanks for those chart excerpts. Those are the FAA charts- which I hadn't checked before my initial post. The Jepp charts for those approaches use the FAP terminology. I find that interesting because my understanding is that Jepp simply converts the government AIP format to their own format- they don't modify the procesures.

Not necessarily. E.g., if flying an RNP procedure using Baro-VNAV then the final approach is commenced at the GS intercept -- which might not precisely match the waypoint lat/long due to altitude variation (with pressure, temperature, ATC instructions, etc.)

This is analogous to an ILS approach where the FAP is defined as the GS intercept point, which on any given day is not always directly above the marker beacon depending on the actual altitude flown.

I've never flown with Baro VNAV, so I hadn't considered it. That makes sense though. I'm planning to email Jepp about an error on a chart, I guess I'll ask why they used the FAP terminology instead of FAF, as the government charts use, at that time. Cheers!

From ICAO:

APPROACH CLASSIFICATION. Approach classifications have traditionally comprised NPAs and PAs. A third classification of APVs is now included. APVs are instrument approach procedures which utilise lateral and vertical guidance but do not meet the accuracy requirements for PAs.

"PANS-OPS Volume I defines an APV as ‘An instrument approach procedure which utilises lateral and vertical guidance but does not meet the requirements established for precision approach and landing operations"

"An APV is characterised by a DA and does not have a MAPt. It may be:
 an addition to a GNSS-based NPA (RNAV(GNSS)), in which case the minima line will be indicated by the term LNAV/VNAV (for Baro-VNAV approaches);
 an augmented GNSS based approach in which case the minima line will be indicated by the term LPV; or
 a procedure designed on RNP principles, in which case the minima line will be indicated by the term RNP XX (where XX will be a number from 0.3 to 0.1 to indicate the accuracy to
which the procedure is designed). Any instrument procedure with an RNP value less than 0.3 will require special authorisation from CASA. These procedures are called RNP AR but
are currently charted as RNAV (RNP)"

https://www.casa.gov.au/file/104796/...token=iTG4MIcl

That is incorrect.

Oops you're right. Or rather, the intercept will always be at same location as the waypoint if flown at the indicated altitude. I was looking at a Jepp RNP chart (noting the GS intercept) and got mixed up when I made that comment.

http://i.imgur.com/q8usSnj.png

Jepp labels RNP AR in the U.S. and elsewhere as FAP. The FAA can pound sand.

The RNP APCH LNAV/VNAV (basically a Baro VNAV) altitudes (hence glideslope position) are based upon the aircraft altimeter subscale (hence temp limits) whereas the ILS glideslope comes from the ground aid.

Curious what Jepp RNP chart lists a waypoint with glideslope intercept?

JABGO is for SFO, right?

http://i.imgur.com/coNl4vv.jpg

I believe they are transitioning to FAP as they slowly revise the charts over time. So, a plate will show FAP or GP intercept depending on its last amendment date. A current cycle example showing GP intercept would be the RNP Y 19L approach at Tampa.

http://i.imgur.com/UirogwP.png

Here is the current Jepp chart for the RNP AR to 19R at KSFO:

It does seem to be a transition from FAF to FAP, I was thinking this was something the FAA was doing to better coordinate with ICAO.

trerpster, get your glasses on, that is 10, not 19!

The GP Intcpt, ...oi vey

The transition is Jepp only, not FAA.

FAP in FAA parlance means something else entirely. On a non-precision approach, FAP is the point where a procedure turn intersects the final approach course. The final approach may be commenced from this point unless a FAF is charted elsewhere.

The glideslope intercept point (ICAO FAP) is called "Precision FAF" (PFAF) in FAA lingo. On an ILS approach the PFAF is charted as the "lightning bolt" symbol on FAA plates, and is almost always at a different location than the non-precision FAF (if any) on the same plate.

For APV approaches, instead of having both a FAF and a PFAF at different locations, the FAA will use a single FAF. And on FAA charts this location will always be charted as FAF, not FAP. There are too many legal rules / regulations which reference "FAF" so it would be a lot of effort to rename it now.

Underfire:

How about typing too fast? The chart does make the point about Jeppesen's transition.

terpster, no worries...

Yes, note back in post #5. Still wondering about peekay showing gp intcpt on JABGO in that procedure profile... the Jepp plate provided by terpster shows FAP....

Am curious what the RNAV visual shows on the FAF/FAP/whatever....

I remember on some of the RNP plates, we were asked to show it as a FAP instead of FAF, but it went back and forth, and most of the plates were RNP AR anyways, so not public.