I am new to this sim, so I’m still trying to figure out what it can, and can’t do.

Although the VNAV function does not seem to work (at least with default aircraft), I’ve discovered that there is a limited VNAV capability with RNAV approaches.

I’m still researching this (and I would greatly appreciate any insight others may provide), but I have found that in many cases, a vertical glide path exists that can be captured and flown down to the threshold by pressing the APR button (I’m testing this with the default Bonanza and Baron).

At first, I thought the path began at the Final Approach Fix, but now, I’m starting to question that premise. It appears that ‘a glide path’ does exist, and if one knows the altitude to intercept it at, they can conduct the rest of the approach with lateral and vertical guidance.

If anyone can provide any more information about this, I would most grateful. I suspect there’s a common variable, but I don’t know what it is.

If a runway has an ILS you can tune your Nav 1 radio to its frequency. Depending on what you are flying selecting loc/nav1 on your CDI once you are in range of the ILS, and then APR mode on the autopilot the AC will follow the lateral directional to the runway. If that ILS has a glide slope (not all do) like runway 09 below, it will also give you your vertical navigation down to the end of the runway. Generally an ILS can be picked up about 25-miles or so from the runway, and the glide slope at about 20-miles. There are some "rules" that need to be followed in order for this all to work, like not intercepting the ILS at too high of an angle, or at too high of an altitude (you should be below the glide slope before it is intercepted). A glide slope <normally> has an approximate 3-degree pitch. If the runway elevation is 0, the glide slope would be at about 6,000' 20-miles out, but generally you would be a lot lower than that on your approach. That's my simplistic description, someone else can probably provide more insight.

 

Edited December 31, 20205 yr by desbean

And yes, there are fixes associated with ILS approaches. Also if the ILS has a DME (all three shown below) it will provide the distance to the runway.

Edited December 31, 20205 yr by desbean

Thanks. Actually, my post has to do with RNAV approaches, and more specifically, the limitations of this sim with regard to how aircraft can utilize them.

There does not appear to be any difficulty in the use of land based nav aids.

1 hour ago, XLS_DRiver said:

Thanks. Actually, my post has to do with RNAV approaches, and more specifically, the limitations of this sim with regard to how aircraft can utilize them.

There does not appear to be any difficulty in the use of land based nav aids.

The simple answer is that RNAV approaches are currently broken in MSFS.

Asobo has said that they will improve the avionics in the February update, and hopefully they will deliver.

In the meantime, the Garmin units look pretty and do not work correctly.

I wish the answer were different, but that is what it is.. 😉

In my opinion, there are too many things wrong with RNAV approaches to use them in any meaningful way... activating an approach can send you on a wild goose chase, all the while with an active glideslope indicator that is pegged at the top or the bottom of the scale without any connection with reality.  In a real airplane, you would put a big INOP sticker on the display. 

Edited December 31, 20205 yr by Bert Pieke

The WT CJ4 handles RNAV approaches well in most cases

RNAV is going to hit and miss in the sim....mostly miss.  If I remember correctly all the fixes or 'types' of fixes don't get read by the avionics.  The Navdata is actually there for the most part it's just not getting used correctly.

6 hours ago, XLS_DRiver said:

If anyone can provide any more information about this, I would most grateful. I suspect there’s a common variable, but I don’t know what it is.

As others have mentioned, the default avionics are not capable of parsing the RNAV data to the extent needed to fly an approach. We have written handling for RNAV and LPV for the CJ4 and these capabilities are coming to the G1000 and G3000 in the next month or so. Links to the aircraft download and our discord community are below of you'd like to learn more or try it out.

Here's an RNAV LPV into KFAT:

https://youtu.be/mW9P9OhA2e0

 

1 hour ago, Bert Pieke said:

The simple answer is that RNAV approaches are currently broken in MSFS.

Asobo has said that they will improve the avionics in the February update, and hopefully they will deliver.

In the meantime, the Garmin units look pretty and do not work correctly.

I wish the answer were different, but that is what it is.. 😉

In my opinion, there are too many things wrong with RNAV approaches to use them in any meaningful way... activating an approach can send you on a wild goose chase, all the while with an active glideslope indicator that is pegged at the top or the bottom of the scale without any connection with reality.  In a real airplane, you would put a big INOP sticker on the display. 

Hi Bert,

Good to see you again.

So, while I won't argue with your basic premise, I have been looking for a work around under the present circumstances and I think I've found it.

Essentially, what I've determined, is that while using the sim in its current form, you have to manually 'dive-and-drive' down to the last fix on the flight plan (the one prior to the airport). At that point, MSFS will allow you to utilize a vertical glidepath down to the the threshold of the runway, using the APR button. I agree, that this is not perfect, and it doesn't work for every airport (it doesn't work, for instance, on the 28R RNAV approach into KMRY), but I have found it works 90% of the time.

I just selected the Rain setting and flew down to minimums at KCCR using the glidepath in this manner (this is probably technically considered LNAV/VNAV and not LPV, but who's quibbling?)

 

So, for those that are interested;

1. Make a flight plan to a destination with an RNAV approach.

2. Select the particular approach you want.

3. While looking at the flight plan, select an appropriate altitude (MSFS almost always assigns too low an altitude for the flight) and pay particular attention to the fix before the airport and its crossing altitude (I write down the fix and the altitude).

4. Conduct the flight but once you arrive in the terminal area, DO NOT use the PROC button or activate any approaches (I haven't had much luck trying to do that).

5. Do the necessary step downs in the instrument approach, descending down to the last crossing altitude and upon approaching the last fix, dial the field elevation for the airport (strictly speaking, I don't know if this step is necessary--I've been doing it simply because it's a standard VNAV SOP) and select APR. The autopilot (or you) will fly the aircraft down to the threshold as it should.

 

Enjoy!

https://www.boldmethod.com/learn-to-fly/navigation/should-you-fly-an-ils-lpv-or-lnav-vnav/

40 minutes ago, Alpine Scenery said:

https://www.boldmethod.com/learn-to-fly/navigation/should-you-fly-an-ils-lpv-or-lnav-vnav/

I think OP is rated on the Citation Excel....

1 minute ago, SAS443 said:

I think OP is rated on the Citation Excel....

I'm still just experimenting with the ILS/VNAV stuff in MSFS, half the time i don't know if I did something wrong, or if it was the particular plane, cannot keep it all straight anymore.

 

No problem using RNAV approaches in general with standard planes such as the c172, c208, or the  3 planes from Carenado without mods of any kind.

I DO use the procedure button prior to take off and select my RNAV approach and initial fix while on the ground and Load the approach.

  I am typically at the minimum for the FAF before the call out from ATC to land having come down from the altitude of the IAF .  I press the approach button typically about 4.2 nm from the airport, or roughly 1 nm before the FAF.

I have had almost zero rejected captures this way, and in the rare case that I do, we just refly the landing.

Edited December 31, 20205 yr by FrankR409

3 hours ago, FrankR409 said:

No problem using RNAV approaches in general with standard planes such as the c172, c208, or the  3 planes from Carenado without mods of any kind.

I DO use the procedure button prior to take off and select my RNAV approach and initial fix while on the ground and Load the approach.

  I am typically at the minimum for the FAF before the call out from ATC to land having come down from the altitude of the IAF .  I press the approach button typically about 4.2 nm from the airport, or roughly 1 nm before the FAF.

I have had almost zero rejected captures this way, and in the rare case that I do, we just refly the landing.

Hi Frank,

I haven’t flown either the C172 or C208, and I don’t have any of the payware aircraft yet.

Do you know if your method works with any of the other default aircraft?

Btw, for what it’s worth, in the aircraft I fly for a living, VNAV would be the mode to use for these approaches, but obviously, that function doesn’t work in the sim. I can’t recall if the approach mode is typically used in GA aircraft for RNAV approaches, but it appears that’s the only way to utilize a GPS glideslope.

6 hours ago, SAS443 said:

I think OP is rated on the Citation Excel....

Now he's typed in some sort of Boeing haha

Anyway the only reliable aircraft I've used that flies RNAV(GPS) approaches is the WorkingTitle CJ4.  All the rest have issues - either making a large sweeping arc to the IAF, not showing the glide path during LPV mins, not descending on the glide path, skipping the IAF to going direct to the FAF.  Sometimes this can be avoided (last part) but adding the IAF in front of the IAF (so seeing it twice in the FPL).