What is the correct procedure to fly a VNAV approach?

[XPJavelin]

After the night a fresher mind helps recollect all the processed data from the docs and help from Rich

 That would be Rvr2800 m if I elected non CDFA for this NPA/2D approach that I elected to study as witness, but I keep 2400M  because it is already the maximum due to the AESA cutoff in table 6A for cat C, and parameters like angular final track within 5deg of runway track and so on. r2400m + 400m - cutoff = 2400m. 

CDFA is required, which I was really ignorant before, I thought it was operator or pilot preferences, even if nowadays aircraft designs instead make naturally opt for the CDFA due to advanced avionics.

By the way, instead of the annex above from 2012, I use the same AESA doc, but consolidated 2022. Easy Access Rules for Air Operations (Regulation (EU) No 965-2012) – Revision 17 (February 2022)_0.pdf

Now,  I am at LFLC RNP Y 26, I  have RVR 1600m.

If I do this non CDFA, I add 400m for my cat C, giving me 2000m and this is inferior to the cutoff 2400 from table 6A.

As I fly less and less 2D approaches, there is a chance I forget about doing the increment while flying...

[XPJavelin]

Now, Rich,

Let's practice for the US.

Let me settle on an example, that would be the KABQ RNP Y 03 in its 2D flavor. (LNAV only).

My LIDO flavor is the one for us customers, as indicated by the TERPS mention, not the LIDO AESA worldwide option, if i am correctly interpretating the LIDO commercial information. 

I see 2400m rvr.

If I'm flying CDFA, no problems, 2400m rvr applies. 

Now if for any reason, I need to do this the old grandPa way :

if I just arrived from Merluchon city, France, and my company is AESA approved, I do 2400mm+400m=2800m, and since this are TERPS I read, I don't apply the 2400m cutoff, since the table 6 is inexistant in TERPS. my minimum is 2800m.

2800m, If I carry candies, merluchons, frogs, or undeclared Goat cheese in my cargo holds.

Now, let's pretend I'm used to the smoke-kissed flavor of freshly roasted green chiles and the earthy fruitiness of red chile sauce, backbone of the New Mexican cooking and I'm paid by an FAA approved airline. (Do the pilots there fly with their Stetson and stirrup ?)

I can see on an original TERPS document the origin of the rvr2400m

As there is no occurrence of the text string CDFA in it, Order_8260.3E.pdf

I can co sider 2400m whatever I choose to do, old grandPa or CDFA. 

(The advisory circular 120 108 on CDFA advises me to opt for  a CDFA with a Derived decision altitude, but this not a regulation and  othing I side concerns visibility)

I am completely wrong in my homework?

Now something that explains the confusion I had in the whole thread, is this page of a jeppesen publication where non cdfa penalty is mentioned in the line TERPS...

Here it's still confusing to stare at this page since I have just  shown the TERPS original document out of the FAA does not mention CDFA.

Finally, if I come back to ICAO DOC 9365, for an MDH of 310 with FALS, I find the RVR of 700 meters... I will need to ditch studying the ICAO doc, and retain only AESA doc versus TERPS, I guess, to keep clear of brain melting I fear.

Edited April 4, 2022 by XPJavelin

[XPJavelin]

Based on your previous help Rich, n' use of the raw and current information  from agencies I'm tempted to correct what is available at Jeppesen AOM publications by :

That would help me find some peace of mind ... it it was correct

Edited April 4, 2022 by XPJavelin

[XPJavelin]

A temporary work (subject to frequent updates to better en-light the subject) of synthesis

 

Getting_to_grips_with_approach_minima.pdf

Edited April 8, 2022 by XPJavelin

[Lightcivvie]

On 3/21/2022 at 10:59 PM, cwjohan said:

I'm trying the RNAV(RNP) Y approach to runway 31L at KPSP.  VNAV kind of works up until the point where the synthetic glideslope should be intercepted, provided one lowers the target altitude setting to below the runway altitude.  Most aircraft permit the target altitude to be set to the glideslope intercept altitude for this type of approach.  Is VNAV actually the wrong way to fly a VNAV(RNP) approach?  How does one select other approach modes?

This thread quickly went from how to fly an RNAV/RNP approach to a discussion of minimums and what CDFA is. I'll give my answer on how to fly the RNAV(RNP) approach, but first:

Most RNAV/RNP and overlay approaches have a descent trajectory that usually leads to 50 feet above the threshold, which has been coded into the FMS database. This means that the Challenger/Collins FMS can provide guidance along that trajectory, and I can fly it just like an ILS (with two HUGE caveats, more on that below).

To check if the descent trajectory has been coded, I look at the FMS legs pages and check the altitudes and angles match the chart. I also check that V-MDA is not shown next to the missed approach waypoint on the right side of the FMS display (this would imply that a descent trajectory has NOT been coded, and I can't use VNAV past the FAF).

TO FLY THE RNAV/RNP APPROACH (compared to an ILS)

To fly an ILS, I set my minimums, and when cleared for the approach, I arm APPR. After GS capture, I set my missed approach altitude.

   On the FMA, I look for LOC1 to become armed, then captured, and for GS to become armed, then captured.

To fly an RNAV/RNP, I set my minimums, and when cleared for the approach, I arm APPR and VNAV, and set my altitude selector to FAF crossing altitude. After GP capture, I set my missed approach altitude.

   On the FMA, I look for APPR LNV1 to become armed, then captured, and for GP to become armed, then captured (as VGP) ***. I also look for GPS APPR on my PFDs.

THAT'S IT!

It's that simple. The huge differences I mentioned? First, make DAMN sure you have the correct altimeter setting set. Second, once you reach minimums on the RNAV(RNP) approach, GP information IS ADVISORY ONLY AND DOES NOT GUARANTEE CLEARANCE FROM TERRAIN. The ILS GS is reliable to a much lower altitude. 

*** see below for why in some cases the vertical mode that initially arms and captures may be PATH and only when closer to the FAF will GP arm then capture.

 

P.S. Now comes the fine print. You want to know the following facts about VNAV. There are 2 modes of interest for descent and approach: (V)PATH and (V)GP.

KEY FACT 1: (V)GP mode is **IDENTICAL** to (ILS) GS mode - in this mode the aircraft will disregard the altitude selector.
KEY FACT 2: (V)PATH mode considers the altitude selector.

KEY FACT 3: (V)GP is only available with APPR mode (shown as APPR LNV1/2 on your FMAs), it is NEVER available in NAV mode (shown as LNV1/2 on FMAs). In NAV mode you will only ever get (V)PATH guidance.

KEY FACT 4: In APPR mode, the FMS may initially provide (V)PATH guidance until sufficiently close to the FAF and lined up on final, then switch to (V)GP mode. 

Finally, there are some more things to consider. If the approach is coded in the FMS to use SBAS (WAAS, EGNOS and co.), the descent trajectory will be the same regardless of the temperature - just like an ILS. If it is NOT coded to use SBAS but only Baro-VNAV, or if it is but you change the approach setting in the FMS to use Baro-VNAV, then the descent trajectory will be affected by temperature (flatter/shallower when cold, steeper when hot. And distance-altitude checks won't help unless you do temperature compensation. But that is another topic altogether). You can see if an approach is SBAS or Baro-VNAV when you have selected the approach from the FMS, by pressing the 'ARR DATA' LSK.

And, check carefully, there may be mistakes in coding of the database - happens more than you think. 

[Lightcivvie]

On 3/21/2022 at 10:59 PM, cwjohan said:

I'm trying the RNAV(RNP) Y approach to runway 31L at KPSP.  VNAV kind of works up until the point where the synthetic glideslope should be intercepted, provided one lowers the target altitude setting to below the runway altitude.  Most aircraft permit the target altitude to be set to the glideslope intercept altitude for this type of approach.  Is VNAV actually the wrong way to fly a VNAV(RNP) approach?  How does one select other approach modes?

This thread quickly went from how to fly an RNAV/RNP approach to a discussion of minimums and what CDFA is. I'll give my answer on how to fly the RNAV(RNP) approach, but first:

Most RNAV/RNP and overlay approaches have a descent trajectory that usually leads to 50 feet above the threshold, which has been coded into the FMS database. This means that the Challenger/Collins FMS can provide guidance along that trajectory, and I can fly it just like an ILS (with two HUGE caveats, more on that below).

To check if the descent trajectory has been coded, I look at the FMS legs pages and check the altitudes and angles match the chart. I also check that V-MDA is not shown next to the missed approach waypoint on the right side of the FMS display (this would imply that a descent trajectory has NOT been coded, and I can't use VNAV past the FAF).

TO FLY THE RNAV/RNP APPROACH (compared to an ILS)

To fly an ILS, I set my minimums, and when cleared for the approach, I arm APPR. After GS capture, I set my missed approach altitude.

   On the FMA, I look for LOC1 to become armed, then captured, and for GS to become armed, then captured.

To fly an RNAV/RNP, I set my minimums, and when cleared for the approach, I arm APPR and VNAV, and set my altitude selector to FAF crossing altitude. After GP capture, I set my missed approach altitude.

   On the FMA, I look for APPR LNV1 to become armed, then captured, and for GP to become armed, then captured (as VGP) ***. I also look for GPS APPR on my PFDs.

THAT'S IT!

It's that simple. The huge differences I mentioned? First, make DAMN sure you have the correct altimeter setting set. Second, once you reach minimums on the RNAV(RNP) approach, GP information IS ADVISORY ONLY AND DOES NOT GUARANTEE CLEARANCE FROM TERRAIN. The ILS GS is reliable to a much lower altitude. 

*** see below for why in some cases the vertical mode that initially arms and captures may be PATH and only when closer to the FAF will GP arm then capture.

 

P.S. Now comes the fine print. You want to know the following facts about VNAV. There are 2 modes of interest for descent and approach: (V)PATH and (V)GP.

KEY FACT 1: (V)GP mode is **IDENTICAL** to (ILS) GS mode - in this mode the aircraft will disregard the altitude selector.
KEY FACT 2: (V)PATH mode considers the altitude selector.

KEY FACT 3: (V)GP is only available with APPR mode (shown as APPR LNV1/2 on your FMAs), it is NEVER available in NAV mode (shown as LNV1/2 on FMAs). In NAV mode you will only ever get (V)PATH guidance.

KEY FACT 4: In APPR mode, the FMS may initially provide (V)PATH guidance until sufficiently close to the FAF and lined up on final, then switch to (V)GP mode. 

Finally, there are some more things to consider. If the approach is coded in the FMS to use SBAS (WAAS, EGNOS and co.), the descent trajectory will be the same regardless of the temperature - just like an ILS. If it is NOT coded to use SBAS but only Baro-VNAV, or if it is but you change the approach setting in the FMS to use Baro-VNAV, then the descent trajectory will be affected by temperature (flatter/shallower when cold, steeper when hot. And distance-altitude checks won't help unless you do temperature compensation. But that is another topic altogether). You can see if an approach is SBAS or Baro-VNAV when you have selected the approach from the FMS, by pressing the 'ARR DATA' LSK.

And, check carefully, there may be mistakes in coding of the database - happens more than you think. 

[richjb]

On 7/22/2022 at 12:09 PM, Lightcivvie said:

This thread quickly went from how to fly an RNAV/RNP approach to a discussion of minimums and what CDFA is. I'll give my answer on how to fly the RNAV(RNP) approach, but first:

Most RNAV/RNP and overlay approaches have a descent trajectory that usually leads to 50 feet above the threshold, which has been coded into the FMS database. This means that the Challenger/Collins FMS can provide guidance along that trajectory, and I can fly it just like an ILS (with two HUGE caveats, more on that below).

To check if the descent trajectory has been coded, I look at the FMS legs pages and check the altitudes and angles match the chart. I also check that V-MDA is not shown next to the missed approach waypoint on the right side of the FMS display (this would imply that a descent trajectory has NOT been coded, and I can't use VNAV past the FAF).

TO FLY THE RNAV/RNP APPROACH (compared to an ILS)

To fly an ILS, I set my minimums, and when cleared for the approach, I arm APPR. After GS capture, I set my missed approach altitude.

   On the FMA, I look for LOC1 to become armed, then captured, and for GS to become armed, then captured.

To fly an RNAV/RNP, I set my minimums, and when cleared for the approach, I arm APPR and VNAV, and set my altitude selector to FAF crossing altitude. After GP capture, I set my missed approach altitude.

   On the FMA, I look for APPR LNV1 to become armed, then captured, and for GP to become armed, then captured (as VGP) ***. I also look for GPS APPR on my PFDs.

THAT'S IT!

It's that simple. The huge differences I mentioned? First, make DAMN sure you have the correct altimeter setting set. Second, once you reach minimums on the RNAV(RNP) approach, GP information IS ADVISORY ONLY AND DOES NOT GUARANTEE CLEARANCE FROM TERRAIN. The ILS GS is reliable to a much lower altitude. 

*** see below for why in some cases the vertical mode that initially arms and captures may be PATH and only when closer to the FAF will GP arm then capture.

 

P.S. Now comes the fine print. You want to know the following facts about VNAV. There are 2 modes of interest for descent and approach: (V)PATH and (V)GP.

KEY FACT 1: (V)GP mode is **IDENTICAL** to (ILS) GS mode - in this mode the aircraft will disregard the altitude selector.
KEY FACT 2: (V)PATH mode considers the altitude selector.

KEY FACT 3: (V)GP is only available with APPR mode (shown as APPR LNV1/2 on your FMAs), it is NEVER available in NAV mode (shown as LNV1/2 on FMAs). In NAV mode you will only ever get (V)PATH guidance.

KEY FACT 4: In APPR mode, the FMS may initially provide (V)PATH guidance until sufficiently close to the FAF and lined up on final, then switch to (V)GP mode. 

Finally, there are some more things to consider. If the approach is coded in the FMS to use SBAS (WAAS, EGNOS and co.), the descent trajectory will be the same regardless of the temperature - just like an ILS. If it is NOT coded to use SBAS but only Baro-VNAV, or if it is but you change the approach setting in the FMS to use Baro-VNAV, then the descent trajectory will be affected by temperature (flatter/shallower when cold, steeper when hot. And distance-altitude checks won't help unless you do temperature compensation. But that is another topic altogether). You can see if an approach is SBAS or Baro-VNAV when you have selected the approach from the FMS, by pressing the 'ARR DATA' LSK.

And, check carefully, there may be mistakes in coding of the database - happens more than you think. 

A couple of quick comments...

On an ILS approach, when "cleared for the approach", do not select APPR mindlessly.   You need to look at what's ahead on the approach leading into the FAF. 

There's a very simple reason.  If you capture the glideslope, following the glideslope will not guarantee compliance with intermediate segment stepdown fixes.  A good example of this is the LD Rwy 25 approach into Eagle, CO (KEGE): 06403LDA25 (faa.gov)  This approach has a glideslope.  You're normally cleared for the approach around RLG or QNDRY.  As you turn final, you may be above GS, maybe not especially on hot day.  If you capture the glideslope, on hot day, you will descend below the stepdown fix altitudes at WEHAL and AIGLE. 

On a long ILS approach like you find at ORD, IAD, IAH, DFW, etc, with multiple intermediate segment stepdown fixes, on a hot day, the glideslope will take you below those altitudes.  Those altitudes are required for the 1000 ft. separation at turn during parallel runway operations.  Back in 2010, after the new runways at ORD opened, there were bunch of CRJ pilots flying Collins aircraft that got pilot deviations for following the training school mantra of "cleared for the approach - arm APPR".  That works the sterile environment of the flight simulator.  It does not work in real life.  

Even the Collins SBAS system can get you into trouble.  There's a little known issue with the Collins SBAS FMS when an RNAV or RNP APCH approach is loaded.  If the aircraft uses the Jeppesen database (the Lufthansa database option is not affected), passing the intermediate fix which is labeled (IF), the FMS will begin using SBAS vertical guidance in place of Baro-VNAV guidance.  And it does not matter if VNAV or VGP is displaying.   SBAS vertical guidance is not affected by temperature, just like the ILS glideslope.  If the temperature is hot, like it is now in DFW, following the VNAV path on a RNAV/RNP approach like the ones on runways 17L/R will take you below the stepdown altitudes.  Nothing can be done about it, except using VS mode.  I've been curious as to whether this is simulated in HS 650???   If you would read more about, refer here: Hist 19-02-344 (faa.gov)

Second, as for the obstacle protection below the DA on an ILS or RNAV or RNP APCH approach to LPV minima, the obstacle protection is exactly the same.  The same is true for RNAV RNP APCH approach to LNAV/VNAV line of minima or an RNP AR APCH to any RNP line of minima.  The TERPS PANS-OPS obstacle protection surfaces are the same once you're below DA.  

Now if you are flying an RNAV/RNP approach to LNAV only minima, then the answer is YES.  There is NO obstacle protection once you descend below MDA.  If you want to find out more about this subject, read this: Hist 12-01-301 (faa.gov)

Best regards,

Rich Boll

 

 

 

[skiselkov]

12 hours ago, richjb said:

I've been curious as to whether this is simulated in HS 650???

We probably don't exhibit this exact quirk/bug. I've got the system coded so it smoothly transitions to geometric vertical guidance only when the approach is an SBAS approach and is being flown in SBAS mode vertical guidance (selected using the mode switch on the ARR DATA page). If geometric vertical guidance is enabled, then from 5NM inbound to the FAF, I start blending the baro-VNAV with geometric guidance, until at the FAF it becomes purely geometric.

As usual, Collins doesn't detail the exact bugs of their code in their user manuals, and so in absence of information to the contrary, I made it do the "smart" thing. Perhaps I should "fix" this and make it do the dumb thing? I'll give the docs you linked a read and think about it.

Edited July 25, 2022 by skiselkov

[Lightcivvie]

On 7/25/2022 at 12:05 AM, richjb said:

A couple of quick comments...

On an ILS approach, when "cleared for the approach", do not select APPR mindlessly.   You need to look at what's ahead on the approach leading into the FAF. 

There's a very simple reason.  If you capture the glideslope, following the glideslope will not guarantee compliance with intermediate segment stepdown fixes.  A good example of this is the LD Rwy 25 approach into Eagle, CO (KEGE): 06403LDA25 (faa.gov)  This approach has a glideslope.  You're normally cleared for the approach around RLG or QNDRY.  As you turn final, you may be above GS, maybe not especially on hot day.  If you capture the glideslope, on hot day, you will descend below the stepdown fix altitudes at WEHAL and AIGLE. 

On a long ILS approach like you find at ORD, IAD, IAH, DFW, etc, with multiple intermediate segment stepdown fixes, on a hot day, the glideslope will take you below those altitudes.  Those altitudes are required for the 1000 ft. separation at turn during parallel runway operations.  Back in 2010, after the new runways at ORD opened, there were bunch of CRJ pilots flying Collins aircraft that got pilot deviations for following the training school mantra of "cleared for the approach - arm APPR".  That works the sterile environment of the flight simulator.  It does not work in real life.  

Even the Collins SBAS system can get you into trouble.  There's a little known issue with the Collins SBAS FMS when an RNAV or RNP APCH approach is loaded.  If the aircraft uses the Jeppesen database (the Lufthansa database option is not affected), passing the intermediate fix which is labeled (IF), the FMS will begin using SBAS vertical guidance in place of Baro-VNAV guidance.  And it does not matter if VNAV or VGP is displaying.   SBAS vertical guidance is not affected by temperature, just like the ILS glideslope.  If the temperature is hot, like it is now in DFW, following the VNAV path on a RNAV/RNP approach like the ones on runways 17L/R will take you below the stepdown altitudes.  Nothing can be done about it, except using VS mode.  I've been curious as to whether this is simulated in HS 650???   If you would read more about, refer here: Hist 19-02-344 (faa.gov)

Second, as for the obstacle protection below the DA on an ILS or RNAV or RNP APCH approach to LPV minima, the obstacle protection is exactly the same.  The same is true for RNAV RNP APCH approach to LNAV/VNAV line of minima or an RNP AR APCH to any RNP line of minima.  The TERPS PANS-OPS obstacle protection surfaces are the same once you're below DA.  

Now if you are flying an RNAV/RNP approach to LNAV only minima, then the answer is YES.  There is NO obstacle protection once you descend below MDA.  If you want to find out more about this subject, read this: Hist 12-01-301 (faa.gov)

Best regards,

Rich Boll

 

 

 

Very good points you make about when exactly to arm APPR. You must be an 'old' Lear 55 pilot ;-) 

Same for the dangers of following SBAS guidance trustingly...

[richjb]

On 11/28/2022 at 4:36 AM, Lightcivvie said:

Very good points you make about when exactly to arm APPR. You must be an 'old' Lear 55 pilot ;-) 

Same for the dangers of following SBAS guidance trustingly...

Lear 35 pilot....

[arrowspace90]

On 3/21/2022 at 7:12 PM, Pils said:

Unlike other aircraft types in the Collins auto flight system VNAV is a modifier on the standard vertical modes (VS, FLC, etc.). It basically instructs the system to respect altitude constraints in the flight plan, and if enabled, use speed targets from the FMS. When descending in VPATH on an arrival and initial approach, similar to an ILS, once the plane is flying towards the final approach point for the RNAV/RNP then one can push the APPR button and VGP will arm/capture. Once active the plane will descend on the final glide path below the preselected altitude. Hope that helps.

I see that you are the guy to go to on the 650.  Yes, I had the same experience as the poster on an attempted RNAV app to KSDL.  In the 737, we didn't ARM APP for a VNAV approach.  It was simply flown in LNAV/VNAV. The altitude of 100 feet above the RWY had to be dialed in and "all the dots connected" (no discos). I wondered if in this airplane it might be also necessary to ARM APP.

[Pils]

6 hours ago, arrowspace90 said:

I wondered if in this airplane it might be also necessary to ARM APP.

APPR/VNAV is the correct way to fly an RNAV approach with Pro Line 21, yes.

[arrowspace90]

12 hours ago, Pils said:

APPR/VNAV is the correct way to fly an RNAV approach with Pro Line 21, yes.

Well I tried this yesterday, and I thought it was going to work.  The airplane responded with additional annunciations that I am admittedly not familiar with.  The approach was a twisting RNAV arrival to KSDL.  The 650 correctly descended in VNAV all the way to the FAF.  Then it actually started down from there in the approach (with the A/P engaged).  But then it descended steeply off the PATH into adjacent terrain.

I know a jet of this sophistication is surely doing all of the non-precision approaches, but VNAV is very difficult to fathom in this airplane.  I had the runway elevation in the window and both APP and VNAV engaged.  What else am I supposed to have?

I do not own a "Normal Procedures" manual for this airplane, so thank you for your response.