RNAV Approaches [answered]

[matpietsch]

@KenG,

one question from my side: How to correctly shoot a LP approach? For example this one here:
https://aeronav.faa.gov/d-tpp/2004/06239RX31.PDF

What is the right way of doing it on the PL21? LNAV and VNAV with altitude set to MDA? Or APPR and VNAV with altitude set to MDA?

I learned that anything with MDA you fly NAV, if it has a DA use APPR.

Thanks a lot.

[marc.delaloy51]

Hello, I have an issue with Rnav app, all my final approach a on the nd green line but always shifted letf or right on P3d rwy.

At departure once aligned on rwy i confirm on CDU "rwy update"and i have the same GNSS position and Sim gps ref.
At arrival the cdu gnss pos has drifted.

any idea?

[KenG]

@KenG,

one question from my side: How to correctly shoot a LP approach? For example this one here:
https://aeronav.faa.gov/d-tpp/2004/06239RX31.PDF

What is the right way of doing it on the PL21? LNAV and VNAV with altitude set to MDA? Or APPR and VNAV with altitude set to MDA?

I learned that anything with MDA you fly NAV, if it has a DA use APPR.

Thanks a lot.

Good question. First off I am no longer working with the development team and cannot answer questions about the MV specifics versions of the PL21.

However, from my memory, MV simulated FMS3000 V4.0. (Rockwell Collins is now up to v4.2.) Version 4.0 of the software did not have the provisions for LP approaches. Thus I would ignore LP approaches minimum line and fly the LNAV minimums with NAV/VNAV.

[matpietsch]

Thanks a lot. The LPV does not arm anyway with LP so I fly them with APPR FMS and VNAV

[freeze1058]

Hi,

I just tried to fly EDDH RNP Rwy 33 using VNAV + APPR mode. Upon approaching FAF SOSAX the indication LPV TERM did not change to LPV APPR:

2020-5-23_21-33-9-97.jpg (201.16 KiB) Viewed 2667 times

Upon passing the FAF the pre-announced PATH and GP modes disappeared and the aircraft memained flying level at 3000 feet.

Any idea what went wrong?

Cheers,

Stefan

PS. Previously EDBH RNAV (GPS) Rwy 27 was performed corectly as described in this post.

[Taguilo]

Hi Stefan,

Checked the PFD message in your image. When LPV TERM info displays in amber it means the approach is not available to fly as RNAV LPV, despite the FMS still giving LNAV and VNAV commands. Even GP arm mode in FGS is in amber, which means VGP won't be available and the aircraft will level off passing the last VNAV altitude constraint, as it happened in your example.

You must always check the condition of LPV TERM/APPROACH, etc messages in PFD.

There are many situations for LPV RNAV app not being available, for example lack or rwy altitude info, which comes from Navigraph data.


Tomas

[freeze1058]

Hi Stefan,

Checked the PFD message in your image. When LPV TERM info displays in amber it means the approach is not available to fly as RNAV LPV, despite the FMS still giving LNAV and VNAV commands. Even GP arm mode in FGS is in amber, which means VGP won't be available and the aircraft will level off passing the last VNAV altitude constraint, as it happened in your example.

You must always check the condition of LPV TERM/APPROACH, etc messages in PFD.

There are many situations for LPV RNAV app not being available, for example lack or rwy altitude info, which comes from Navigraph data.


Tomas

Hi Tomas,

thanks for the explanation.

First of all I found a long but excellent Youtube video about this topic at https://youtu.be/O5q71bECrT4. It's a good feeling that apparently also real world pilots have trouble understanding the whole matter

Leaving LPV with VGP aside for a minute and concentrating on an LNAV/VNAV minimums approved procedure using VPATH:

• Will the aircraft (Milviz application, not the real world one) descend from the FAF down MAP or runway with the given Navigraph data upon activating VNAV and altitude set to MDA/DA?

• What are the pre-conditions and how can I identify the ability upon loading procedure in FMS-3000?

Cheers,

Stefan

[freeze1058]

Hi Tomas,

I just tried LNAV/VNAV at KHHR RNAV (GPS) Rwy 25. VNAV with VPATH was activated from beginning with altitude set to DA(H). Aircraft followed the path until FAF ZANIR but then didn't descend further but remained in VALT at 1500 feet:

2020-5-26_21-56-27-741.jpg (415.34 KiB) Viewed 2605 times

I'm wondering if this relates to Navigraph data, because in PMDG 737 NGXu this type of approach usually works and FMC also displays the runway elevation.

Thanks for your feedback.

Cheers,

Stefan

[Taguilo]

Leaving LPV with VGP aside for a minute and concentrating on an LNAV/VNAV minimums approved procedure using VPATH:

• Will the aircraft (Milviz application, not the real world one) descend from the FAF down MAP or runway with the given Navigraph data upon activating VNAV and altitude set to MDA/DA?

• What are the pre-conditions and how can I identify the ability upon loading procedure in FMS-3000?

Hi Stefan,

In NAV mode (green FMS message on FGS), when descending in VNAV mode, aircraft will level off at the last altitude constraint, which usually is the FAF or MAP, providing Preselector altitude is at or below the waypoint altitude.

In APP mode (APPR FMS message on FGS), when descending in VNAV VGP mode, aircraft will NOT level off at MDA point, it will continue down to the runway unless other pilot action is performed.

Preconditions to expect a LPV approach, with VGP vertical guidance ? When LPV Term displays in green as PFD messaffe and GP in white (armed) once APPR mode is selected in FGS. If any or both show in amber, VGP won't be available.


Tomas

[Taguilo]

I just tried LNAV/VNAV at KHHR RNAV (GPS) Rwy 25. VNAV with VPATH was activated from beginning with altitude set to DA(H). Aircraft followed the path until FAF ZANIR but then didn't descend further but remained in VALT at 1500 feet:

Hi Stefan,

You forgot to select APP mode, therefore descent remained in FMS mode.


Tomas

[freeze1058]

Hi Tomas,

In NAV mode (green FMS message on FGS), when descending in VNAV mode, aircraft will level off at the last altitude constraint, which usually is the FAF or MAP, providing Preselector altitude is at or below the waypoint altitude.

OK, clear.

In APP mode (APPR FMS message on FGS), when descending in VNAV VGP mode, aircraft will NOT level off at MDA point, it will continue down to the runway unless other pilot action is performed.

Clear, but I want to test VNAV only, which is why I consciously didn't engage APP mode

Preconditions to expect a LPV approach, with VGP vertical guidance ? When LPV Term displays in green as PFD messaffe and GP in white (armed) once APPR mode is selected in FGS. If any or both show in amber, VGP won't be available.

No, I'm still with VNAV

My problem is that the last fix/constraint always appears to be the FAF for the approaches I tried. If the MAP or runway fix/constraint is missing I cannot achieve VNAV guidance on the final approach, because it ends at the FAF. This makes the LNAV/VNAV minimums unusable upon reaching the DA/MDA, since I'm not in VNAV conditions anymore and would have to take the fallback to LNAV only minimums.


Comparing with the PMDG 737 NGXu by loading KHHR RNAV (GPS) RWY 25 procedure the legs page looks like this:

2020-5-27_3-57-54-774.jpg (69.97 KiB) Viewed 2595 times

They have an altitude constraint entered for the RW25 fix at 116 feet, that enables VNAV guidance from ZANIR (FAF) to RW25 (Runway).

Why doesn't this constraint exist in the King Air?

Cheers,

Stefan

[Taguilo]

Stefan,

The KA and 737 FMS are different units, and therefore it is possible that some info could be present in a different way.

In the KA, you will see "LPV TERM" in PFD when an RNAV procedure supports LPV minimums.
However, to effectively fly upon those minimums in VGP mode FGS must be in APPR FMS, not FMS.
Despite runway altitude is not displayed in Legs page, when flying VGP path the aircraft will descend until reaching the MAP. In most cases it is the runway threshold itself, or a wpt very close to it.

Tomas

[freeze1058]

In the KA, you will see "LPV TERM" in PFD when an RNAV procedure supports LPV minimums.
However, to effectively fly upon those minimums in VGP mode FGS must be in APPR FMS, not FMS.
Despite runway altitude is not displayed in Legs page, when flying VGP path the aircraft will descend until reaching the MAP. In most cases it is the runway threshold itself, or a wpt very close to it.

OK, so if we take this as granted it means that when LPV is not available I need to stick to LNAV minimums, right?

What still confuses me is the availability of LPV at some airports especially outside USA:

If you look at EDBH RNAV (GPS) RWY 27 approach there is no WAAS support and no LPV minimums published (some other German airports have, but not this one). Still I was able to fly LPV with VGP and the FMC ARRIVAL DATA page shows:

2020-5-27_23-18-35-372.jpg (93.14 KiB) Viewed 2568 times

Is this a limitation of Navigraph data?

Stefan

[Taguilo]

It is a limitation of Navigraph and also all FMS RNP procedures are signed as WAAS, which in RW only applies to North America. In Europe should say EGNOS instead. This is something that might be updated in a future SP (no promises).

In MV KA, any RNAV procedure can be flown with LPV minimums (ie with VGP descent), except those that lack critical data (LPV TERM displays in amber instead of white/green).


Tomas

[admin9]

Just reading all of the above as I also find the aircraft levels off at FAF. Can someone please explain how to arm APP mode and not just APPR FMS that is displayed when pressing APPR button prior to the GS. Thank you.