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RMF

Intercept RNP APCH with vectors to final

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Hi there.

 

I've been doing some tests and some research here and there about this, but with no success so far.

I'm trying to intercept a final RNP APCH course from ATC vectors.

 

Let set the situation. Airport doesn't matter, but let say I'm going for an RNP APCH at LFBA, RWY 29. ATC takes me on radar vectors, from south, towards the final app.

In MCDU, RNAV 29 is selected. APPR MODE is as well active, all speeds and data are set for the arrival airport, aircraft is configured correctly (IAS 180kts, Flaps 1, LS is off).

 

I'm now stabilised at 2500ft, well before FAP. ATC gives me a "left heading 320 to intercept final approach course, cleared RNP APCH 29". I'm so on an intercept angle of 30° left of final course. This heading is leading more or less 2NM before FAP.

How do I capture the final course on this heading? Do I have to turn manually (I mean "selected") approaching the extended centerline?

 

I tried multiple options

  • pushing the APPR FCU button once established on the intercept heading, but the aircraft went through the axis without intercepting.
  • setting a direct to IF or FAP on the F-PLN page, then engaging NAV mode, but then of course it turns the aircraft towards the selected point, and is not following anymore the intercept heading

 

So basically, am I doing something wrong? Or simply the bus is not able to perform an "IAN-like" RNP approach (IAN - Boeing terminology for ILS-like approaches).

Then, if bus is not able, how do pilots in real life do when vectored to final course to intercept again managed approach?

 

I do have latest bus version 1.2.5.0, on P3Dv4.5+Hotfix, latest Navigraph AIRAC, ...

 

Thanks for your help!

 

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Hello RMF,

I did some testing and there seems to indeed be an issue where in heading mode if APP NAV is armed the aicraft does not follow the Final Approach Course when intercepting with the NAV path. I will pass this forward and we'll have a look into it once we get a chance.

However above is only the case if the heading intercepts with the NAV path (in heading mode shown with dashed green line). If the aircraft heading does not intercept with this NAV path the aircraft would not know where the path actually is unless you tell it. For example if the IAF is 10nm out from the airport and there is no path before the IAF and you are to intercept the Final Approach Course (FAC) 15 miles from the airport the aircraft would not intercept and you need to do something about this. The answer is Radial In function on the DIR page.

With radial in you can make an extended centerline inbound to the FAP on FAC (FAC - 180°) and if you are on heading mode and on intercept heading less than 160° from the FAC you aircraft will compute a interception point for you where the extended centerline meets with the current heading.

So the two ways possible are:
1) Pushing APPR button to arm APP NAV mode and if flying heading that intercepts with a path that is already on the ND, the aircraft should activate APP NAV automatically and turn to FAC. (We'll have a look into it)
2) If on intercept heading that does not intercept with the current path on the ND you can use radial in function to create artificial intercept point on the extended centerline and that will get you there.

One way to get around the issue with number 1 currently is to use direct with radial in anyways from FAP or do the direct to FAP when you estimate is a good place to start the turn close to the extended centerline.

Hope this helps :)

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Thank you Secondator for your clear and complete answer.

 

Not being an expert of Airbus, I didn't know about the "not intercept case" if heading is leading outside a dashed NAV path.

However, your answer says it all, I'm glad you'll look at it when you will have time. In the mean time, I will exercise the Radial In method for my RNP approaches.

 

Thanks a lot!

Cheers ;)

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I’ve seen the same behavior as well, glad this thread beat me to it.

 

I’ve been experimenting with DIR-TO/Radial IN as well but have been coming across odd responses with it recently.  Programming a radial inbound (roughly 30 degree intercept to final approach course) on an RNAV 4R approach into DTW, MCO 18R, and DEN 16L so far, the fixes on the approach sequentially delete themselves....you can watch it happen about 3 seconds apart.

 

In other words, with managed speed, altitude, and NAV selected, the IN-BND and intercept fixes display correctly on the ND very briefly then every waypoint will delete itself afterward one at a time.  Eventually, the aircraft slowly turns direct the runway selected, but trying to reload an approach then causes a hard CTD (nothing in the error logs either), so if I get into that situation, I’m forced to disconnect AP and fly visually.

 

I know that’s vague, and very odd, as I’m trying to still recreate and investigate but does anyone else have see this issue?

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