RNAV GNSS approaches

[aterpster]

Underfire:

The criteria simply states 30 seconds of stabilised flight, and that can include turns.
FROP can be at 500 feet, with a FAF at the beginning of the turn.

I can only speak to FAA public criteria for RNP AR. (I know Alaska Airlines has their own world of special, "fleet specific" performance-based criteria):

1. DA cannot be in a turn.
2. At least 15 seconds of flight from the FROP to the DA with a non-RNP missed approach, at least 50 seconds with a missed approach of less than RNP 1.0.

[underfire]

yes, the FAF can be at the beginning of a turn, with 30 seconds to the DA. The 30 seconds was for when the FAF was at the beginning of the turn. 50 seconds of stabilised flight before the DA, jeez.

We use 15 seconds of stabilised flight from FROP to DA, with the RNP missed. I do not subscribe to the common concept that on a 0.1/0.3 RNP, you go missed and the world falls apart to a 1.0 RNP (which half of the time gets the tower as an obstacle and the DA is unusable).

Many variables and if/then scenarios to consider.

[Goldenrivett]

Hi underfire,

I do not subscribe to the common concept that on a 0.1/0.3 RNP, you go missed and the world falls apart to a 1.0 RNP (which half of the time gets the tower as an obstacle and the DA is unusable).

How did we all cope when doing a GA from an ILS APP using only heading initially?

Unless your tower is outside the airfield boundary and close to the approach path, it won't be a problem. You commence the GA from a DA which is on the final approach and beyond the airfield boundary.

[Ian W]

Originally Posted by underfire

yes, the FAF can be at the beginning of a turn, with 30 seconds to the DA. The 30 seconds was for when the FAF was at the beginning of the turn. 50 seconds of stabilised flight before the DA, jeez.

We use 15 seconds of stabilised flight from FROP to DA, with the RNP missed. I do not subscribe to the common concept that on a 0.1/0.3 RNP, you go missed and the world falls apart to a 1.0 RNP (which half of the time gets the tower as an obstacle and the DA is unusable).

Many variables and if/then scenarios to consider.

It would be nice to see the genesis of some of these grandfathered in restrictions. Just looking at the calculations made for RNP accuracy and comparing that to the calculations made when building procedures and the mismatch in assumptions is enough to raise significant concern about lack of joined up thought. Taking 'finger in the air' assumptions then using them in complex formulae with false precision inside tools like TARGETS doesn't help. Logic seems to have been abandoned.

[aterpster]

underfire:

yes, the FAF can be at the beginning of a turn, with 30 seconds to the DA. The 30 seconds was for when the FAF was at the beginning of the turn. 50 seconds of stabilised flight before the DA, jeez.

As you know, with an RNP missed approach (less than 1.0) the LNAV needs to be engaged. My FAA friends tell me the 50 seconds is required to accommodate some models of the AirBus. Beats me, I have no first-hand knowledge.

We use 15 seconds of stabilised flight from FROP to DA, with the RNP missed. I do not subscribe to the common concept that on a 0.1/0.3 RNP, you go missed and the world falls apart to a 1.0 RNP (which half of the time gets the tower as an obstacle and the DA is unusable).

I don't follow you. We have lots of RNP AR approaches with minimums of less than 0.30 that do not have RNP missed approaches. One example is KGUC RNP Rwy 24, where only 0.10 would work in the final segment, but then the terrain opens up for a conventional TERPs missed approach.

http://aeronav.faa.gov/d-tpp/1607/00517rr24.pdf

If a tower creates an issue, with FAA policy, then an RNP missed approach is used to avoid it. Or a climb gradient, or a combination of both.

[underfire]

I know you can have RNP approach without RNP missed, especially with the 1.0 RNP missed gathering so many obstacles, and a turn, well, just forget about that containment area...(Imagine Cuzco designed that way!)

I am not aware of any AB variants that require 50 seconds for the missed approach to engage. That was certainly not the case in any of the flight vals on the A320/A380 that I was on...

I was referencing the tailored RNP approaches that are for an airline and not public. In those, part of the service was to design the missed and the EO missed. In these, the same RNP level carries through the missed.
As you are aware, there is no FAA or ICAO criteria for EO procedures, so those are all custom.

I see that the RNP procedure into JFK has a DA in a turn! (FROP is 0.8nm from the TCH, 250HAT!)

[aterpster]

underfire:

I know you can have RNP approach without RNP missed, especially with the 1.0 RNP missed gathering so many obstacles, and a turn, well, just forget about that containment area...(Imagine Cuzco designed that way!)

Cusco should have a line of minimums with a lower DA for the folks that have the performance. The density altitude is a problem for many, but not all, airframes.

I am not aware of any AB variants that require 50 seconds for the missed approach to engage. That was certainly not the case in any of the flight vals on the A320/A380 that I was on...

The way it was explained to me, there had to be at least 50 seconds of flight on a TF leg from the FROP to the MAP, or there was some type of issue reengaging LNAV for the miss. As I said before, I don't have actual knowledge of the issue. I do know it almost prevented a good design at KGUC Rwy 24.

I was referencing the tailored RNP approaches that are for an airline and not public. In those, part of the service was to design the missed and the EO missed. In these, the same RNP level carries through the missed.
As you are aware, there is no FAA or ICAO criteria for EO procedures, so those are all custom.

Lots of variants outside the U.S. I see Australia has EO procedures associated with their RNP AR approaches.

I see that the RNP procedure into JFK has a DA in a turn! (FROP is 0.8nm from the TCH, 250HAT!)

Indeed that one does, but it is a Jet Blue special, not a public procedure. Jet Blue had to do some demonstration flights to convince FAA's Flight Standards that Jet Blue's airframes and crews could safely perform that maneuver. Hopefully, someday the FAA will accept DA in the turn as public criteria. That Jet Blue procedure would be much more useful if everyone flying into JFK could do it. Rolling out at 250 HAT is something that did not make some folks at the FAA very happy. But, Jet Blue prevailed with the people that held the authority.

[underfire]

Lots of variants outside the U.S. I see Australia has EO procedures associated with their RNP AR approaches.

Of course. AUS was great to design for, instead of studying, the procedures just happened...Those started as the tailored designs for QF, then were made multi-variant to some extent. Most of the good EO missed went away, especially with the temp limitations, because of public outcry with "aircraft on fire" going over their house.

[OK465]

The JB special was accepted because JB was the first to get TOGA to Managed Nav capability on their 320s (equivalent to TOGA to LNAV on the NG).

You've got to have this going missed off an RF turn. Without it, when you TOGA (previously to heading or track) the FMS arrived at an average heading over some previous time increment on the RF which resulted in a turn reversal off the RF.

Did 100s of hours of DA in a Turn simulations directed at making the option available for public use. Happily I don't know where that stands now.

[aterpster]

OK465:

The JB special was accepted because JB was the first to get TOGA to Managed Nav capability on their 320s (equivalent to TOGA to LNAV on the NG).

Knowing virtually nothing about a 320, what is its behavior in this respect if it does not have Managed Nav?

[OK465]

The older software resulted in a lateral straight track mode becoming active for both FD & AP when the TOGA detent was selected in the 320/330 or 340 on the RF. The requirement with the DA in a Turn is to stay on the RF during the missed, the Nav selector had to be manually re-engaged (pushed in) to get correct missed steering commands for the FD/AP, by which time the FMGEC had computed the initial straight track in the opposite direction off the RF based on 'an average' of the previous continually changing tracks on the RF itself and supplied this to FD/AP. Unacceptable cross track errors were occurring prior to manually engaging the Nav mode for continuity on the RF in Managed Nav. Depending on where the DA is placed, I have seen the initial lateral steering commands on the 13R transition, if followed, point directly at JFK Tower on the missed. Managed Nav is LNAV equivalent.

Now the FD/AP commands in TOGA to Managed Nav are for staying on the RF to the MApp profile and tracking in Managed Nav on the missed. Coded track continuity maintained.

In the 738, the older software resulted in TOGA to heading, and the FMS provided to the FD/AP an 'average heading' over some previous time increment on the RF, resulting in an opposite direction turn off the RF. Hence updated software with TOGA to LNAV to avoid delay with re-engaging LNAV.

First time I saw this was way back in the 738 with a TOGA actuation on the left RF prior to the FROP performing the PSP procedure. On AP, aircraft reversed the turn direction to the right and headed for the Dino Martin memorial mountains.

[underfire]

Concur, when first looking at these, the B models wanted to go straight to the endpoint of the rf turn, rather than follow the turn. This was problematic at places, especially when the included angle was more than 90 degrees. Was a real issue at Kelowna. (did not have these issues with the A models)

Was that the Naverus PSP procedure or the later public procedure? I think it must have been the later, because with the original AA procedure, the 738 was too slick and would bust the final turn..

[underfire]

ahhh. okay...that makes sense.

It was fun, well, sort of. Dont remember a turn intercept, except in the sim when flight validating, not wanting to run the whole procedure again...

Tried for a few weeks to get the Smith box to take a RWY over 10K, PIN, offsets, anything, just would not do it. Then some variants of the 320 would not keep the descent profile, and would dive to the next waypoint altitude.

The really complicated procedures are still out there, especially in China (as shown by the Lhasa/Lhize type procedures.)

As shown by some of the threads on pprune, the drivers come up with some combinations/events that would be difficult to think of in the validations.

Currently, I am working on the RNP transition to GBAS final procedures, which brings back the old days with a bit of fun in the mix.

[aterpster]

ok465:

First time I saw this was way back in the 738 with a TOGA actuation on the left RF prior to the FROP performing the PSP procedure. On AP, aircraft reversed the turn direction to the right and headed for the Dino Martin memorial mountains.

AKA, Mother Sinatra memorial mountains.

Having said that, part of RNP AR training is not to go to TOGA until the MAP in the event of an early missed approach. Really no different than in any missed approach. Climb, but maintain final segment track to the MAP.

Some foreign countries are quite specific on the chart. At WAPP, for example, the chart states: "Missed approach transition to missed approach RNP for lateral guidance must not be initiated prior to the along track position of DA/H."

[underfire]

I looked at doing WAPP and WAMM, they balked at the cost of the survey for the ICAO obstacle area.

Who ended up doing these?

[aterpster]

underfire:

I looked at doing WAPP and WAMM, they balked at the cost of the survey for the ICAO obstacle area.

Who ended up doing these?

Don't know. But, they are public, both as to charting and database.