Why does ATC not allow some approach transitions to be selected?

[simulondo]

Hi everyone:

I'm thinking about updating some airport approaches but before, I want to ask you about one thing I don't understand about default ATC logic (both FS9 and FSX).

In several airports I cannot select the approach transition I had planned previously. These transitions do exist, I can see them in the GPS, ADE or Plan G, but they don't appear in the ATC menu.

Searching for information about this problem, I've seen in several places that the only solution is to duplicate these transitions as RNAV approaches.

For example, simwings' LEMD distributed by aerosoft: if you approach to RWY32R from east, when ATC offers you vector to land, you can't select ILS32R approach using ASBIN transition, it doesn't appear in the menu. But, if you select RNAV32R, the ASBIN transition appears and you can select it without any problem.

It happens the same with the stock version of LEMD (obviously with very old approaches). If you are approaching from east to land using RWY36R, it's not possible to select the CANES transition. As the stock airports don't have the duplicated RNAV approaches, the only option is to follow the ATC vector instruction.

I'm sure this is for a reason. Maybe ATC doesn't offer you the transitions which are close to the vectors they offer you initially?

As usual, thank you for your time.

Best regards and stay safe.

 

[simulondo]

Hello again,

Maybe if I explain this problem with images, it will be easier to understand.

This example is using FS9 with the stock version of KPDX. No addons.

Approaching KPDX following STAR HELNS3 (very old approach, as I'm using stock airports)

ATC directs me to RWY10L

Then, I open the approaches menu, and select ILS RWY 10L

But there is not any approach or transition available:

Although in the gps you can select it (BUXOM)

Even in Plan-g it appears too

In the simcharts for FS9 appears too

As I said in the first post, this happens with several approaches. And the only solution I've found is to replicate the approach as RNAV. Then, you can select it without any problem.

Before I start to create approaches, I want to understand this problem. I don't want to think that this is a bug. Some reason must be behind this kind of behaviour.

Thank you for your time.

Regards

 

[simulondo]

After reviewing a lot of posts, here and in Avsim, particularly helpful those wrote by Jim Vile and Reggie Fields, and if I've understood correctly, I've come to the conclusion that only the approaches/transitions with Fix Type VOR/NDB will be show in the ATC menu.

Instead, those that have a type fix WAYPOINT or TERMINAL_WAYPOINT won't be shown in the ATC menu. In these cases, you'll be "funneled" by ATC and its "newbie" vectors system (as they call to this option).

Back to the KPDX example, if you open the stock airport in ADE, you can see that the transition BUXON for the approach to RWY10L, its Fix Type is WAYPOINT:

Checking other KPDX approaches, we find in the RWY28R has two transitions:

BTG (VOR):

And LAKER (TERMINAL_WAYPOINT):

if we check in FS2004:

Only appears the BTG transition

I don't understand this limitation, when these approaches do appear in the GPS, so they're selectables. Maybe there is a IFR rule that I don't know or understand about approaches. If someone can clarify this point I'll really appreciate it.

As far as I've found, as I previously said, the only solution to be able to select these approaches, it's to replicate them as RNAV. I don't like this method, but it seems the only one that works.

 

[simulondo]

Reading carefully some Reggie Fields' posts at AVsim, I've realized that he always recommended, when you are creating your flightplans, check the approaches at your destination airport. If one of them is suitable for your plan, add its waypoints into your flightplan.

After append into my flightplan the BUXON fix of the RWY10 ils approach, I obtained this:

It finally appears

So, if you want to interact with the ATC using an approach/transition, your have two ways:

1) Add, at least, the first point of the approach/transition into your flightplan. Not always have to be a IAF fix. The problem of this method: if when you arrive at your destination, the active runway may be different to the one that you previously had planned.

2) Replicate the ILS approach as RNAV if you don't want to add previously those waypoints into your FP, particularly in long distance flights, where there are more possibilities of weather changes. Anyway, I have to test more carefully this method with all this knowledge that I've just learned. Another thing about RNAV approaches is the ATC assigns you some kind of priority over the other AI flights. I don't know much more about this point, I have to investigate more about it.

So, from the perspective of the designer, it seems necessary to not only create (or update, if we talk about old airports) the standard approaches, but also its RNAVs version.

Again, if someone has more information about this stuff, please don't hesitate to correct me, I'll appreciate it.

 

[simulondo]

I've been playing a little bit with ADE, changing the KPDX RWY10L ILS approach type.

From this:

Into this:

from a ILS approach into RNAV approach.

Then, in FS2004, using a flight plan without any waypoint from the approach:

the rnav for the rwy10 appears correctly

and its transition too.
So this confirms that the RNAV approaches are available in the ATC menu, even without adding any waypoint from the approach into the flight plan.

For those standard approaches which their initial fix aren't a VOR, it's mandatory to add, at least, their first waypoint into the flight plan if you want to interact with the ATC, instead to follow its "novice" vector system.

The reason for this behavior: I don't know. I hope someone can clarify this situation.

Best regards