ILS/LOC Mode/APPR mode

[IlanMoshe]

Hello,

When ATC gives me a radar vectoring to capture the ILS and not to follow the STAR or the transition published, the last clearance should be like:
"AFR200, fly heading 070, cleared ILS RWY 04 L".
So, as a pilot, I set heading 070, and press on LOC or APPR and have to wait to the capture of the ILS.
But, the A320 NX behaves quite differently, indeed after be stable on 070 and pressed on LOC/APPR mode, it seems that it starts to capture the ILS even though it didn't cross the radial.

Someone can help me with this.

Thank you

[riveroalbert]

As far as I'm concerned LOC mode will calculate the intercept heading, (i think arround 30 degrees) which might differ from the ILS intercept heading given by the ATC. So I guess to avoid overshooting the ils, FCU makes its own calculation. Could it be that?

[IlanMoshe]

"You can use the navigation mode in combination with the heading function to fly an assigned heading to intercept a course. The procedure illustrated in Figure 4-13 takes advantage of the ability to arm the navigation mode while the heading mode is engaged." P11

"As the autopilot captures the course, the heading function automatically disengages, and the navigation function switches from armed to engaged." P12 (picture)

From : https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/advanced_avionics_handbook/media/aah_ch04.pdf

So if I understood correctly, only when capturing, the airbus LOC approach became "engaged" and therefore has to start the turn.

[IlanMoshe]

I'm not talking about the case showed on this tutorial ;)
He pressed on LOC during the final turn .. I'm talking about pressing LOC when I'm flying, stable on heading 070 to intercept ILS 04 and I'm some miles before the localizer for example.

[ExampleWasTaken]

That file does not refer to the A20N.

[IlanMoshe]

I think we have to separate the phase when the LOC is armed and the phase when the LOC mode became engaged.
When you press on LOC, you're arming the LOC but it is not necessary and immediately became engaged.
It will pass as engaged once it will intercept the localizer.

Think the APP controller should create the sequence via one point which is not on the final approach path.
So, if he gave you the instruction to fly HDG 070 to intercept the ILS 04L, you must continue to fly 070 until the interception, meaning arm the LOC should not deviate the airbus from 070 until the interception.

[ExampleWasTaken]

Alright, I think I know what you mean.
Pressing the LOC button will arm the LOC mode. Following that the FMA display LOC blue. The airbus will then start to fly in a manner that allows it to intercept the localizer at an optimal heading/track. Once it's close enough to the localizer it will change to LOC* meaning it starts to capture the localizer. Once established the FMA displays LOC.

If you are not yet cleared to intercept the LOC you don't press the button yet. Same goes for the APPR pb.