A320 Earlier activate approach phase

[Alton77]

According to the FCOM3, approach phase should be activated either by automatically over Decel way point or manually around 15 NM from touchdown.

What if the Approach phase is earlier activated, may be > 100 Nm from touchdown? Few of my colleagues ignore the SOP and I want some reason to explain them but I can't find in the FCOM.

As I notice, it will cause some inaccurate predictions on FMGS?

1. Level off sign?
2. Vls , I heard that FMGS calculate Vapp from Actual GW instead of predicted landing weight, isn't it?

anybody has anything else?

[Dream Land]

You are correct about the predictions, I will occasionally do this at this distance when I want to operate the remainder of the flight with automatics off, I will then manage the speed so I don't have the speed bug.

[pensador]

Lets step by step. I've just left the TD and the a/c is in DES, NAV modes.
So I ask to PNF to activate appr phase. That will force me to select speed.
I should remenber that the speed in MACH mode. The first load for me.
The second problem I encounter is speed constrain monitoring and executing
by my self!
Continue: when THR IDLE appeared on FMA the FMGS ask me
about more drug or I may increase speed to maintaine vertical profile. That leads
to excessive speed carrying that requires additional distance to be then vanished.
The third proublem is calculation of additional distancefor that.
The EXP DES mode are no longer available.
As I mentioned the prediction accuracy of descent (the blue hook on PFD)
is acceptable to peform approach. The FMGS takes into account all
altitude constrains. I think that's it. CON RESPECTO

[zonak]

Facts:

DESCENT SPEED PROFILE
"If the pilot reverts to the SELECTED speed/MACH mode during descent, the profile is not modified and the aircraft flies the same profile as the FCU-selected speed/MACH value."

PERF APPR PAGE
" F, S, GREEN DOT and VLS speeds computed by the FMGS assuming landing weihgt. NOTE: VLS is the VLS of the selected LDG CONF (3 or FULL ).

INITIAL APPROACH
"You will activate manually the approach phase on the PERF page if:

• HDG or TRK mode is engaged or
• if you are flying a go around or
• if an early deceleration is required"

Above text is to understand there's no false predictions (inacurate) provided winds aloft are entered. Use of selected speed is feasible when hot and high or being vectored. And that's the point where you don't want to be cought by surprise when speed managed is set for deceleration or final approach. Think in pair... speed selected, activate approach phase... HDG or TRK, activate approach phase.

Brgs!

[9.G]

Alton77, without immersing myself too much into technical aspects like predictions etc. There's one golden rule in aviation "do it as per SOP" unless safety dictates otherwise. Often it's beyond our understanding or even intentionally left out from explanations in order to make the pilots life actually easier one. Just as a axiom there's no need for a reason to follow meticulously the SOP. In fact it was written using bad experience of others, that's reason enough for me.
Cheers

[aulglarse]

speaking of bad experiences, activating the APP phase while on descent using EXPED will not revert to min clean but stay at EXPED.