Airbus approach phase activation

[Macarto]

Good Day Gentlemen,

There has been some debate over when the activation of the approach phase should be activated during the course of descent down to the destination.

I have list down a few factors of considerations and techniques to determine when the approach phase should be activated and I hope you can provide your individual insight and opinion over when and how one should determine the period for the activation of the approach phase.

Scenario 1
High Speed descent, ATC Speed restrictions or A/C not abiding by speed constraints in managed mode, PF sets selected speed.

Activates approach phase early in the descent after PF approach brief to get it out of the way and continues on select speed. Sets speed to managed when he/she plans to decelerate to greendot speed. Eg 300kts to Greendot, an approximate distance of 10nm assuming nil wind conditions. Plans to start configuration of A/C at 20nm thus activates approach phase at 30nm to touchdown.


Scenario 2
Delayed activation of Approach phase.

Activate approach phase only when you want to managed speed. Practice is to set managed speed right after the activation of the approach phase. Reason for this is because the sole purpose of activation of approach phase is for the A/THR system to provide auto-speed. Thus it wouldn't make sense to activate it when you want to keep selected speed and not allow the A/THR system manage speed or when you're not ready to use it.

Also, you don't want to be dragging the aircraft at greendot speed if you activate it early on the descent all the way to the point at which you plan to configure the aircraft for the approach. If you did, PF will have to have to pull speed and select above greendot to ensure you are not descending to slowly admist all the traffic behind you.

On that note, why activate the approach phase early on to get it out of the way when you're not ready to use it and pull speed after, it is additional workload.

Worse case scenario, PF forgets to manage speed on approach as sometimes he manage speed after activation of approach phase and sometimes he doesn't, lack of inconsistency can bring about such errors during high workload situations.


I hope what I've mention makes sense and do provide your 2 cents worth, your insights is very much appreciated.