A320 FMS phases

[Black_Dawn]

Hello
the other day we were cruising and decided to descent without autoplilot.
So we disconnected the autopilot, both Flight Directors OFF, and Bird ON, we kept only the AutoThrust, so on the FMA, SPEED was the only annunciated mode.

After a while, during descent and less than 180nm from our destination, we realized that the FMS mode was still in CRUISE phase.
We pulled and pushed on the altitude selector, even the vertical speed we pulled, to no avail.:* We were able to select the APPROACH phase, but that really was simple: you have just to push the appropriate button on the MCDU

My question is: must we have the FD's on, for the FMS to change its flight phase, or what?

thanks B_D

[Checkboard]

Why did you want DES phase, if you didn't want FD guidance? :confused:

Just curious.

[Black_Dawn]

Because this way I can still have predictions where the level-off will be (blue arrow) and start of the new descent (white arrow), along the route. And I think about fuel predictions too.

But really my question is can I force the DES phase in this situation or am I missing something?

B_D

[Field In Sight]

Both FDs OFF:
‐ The FD bars disappear from both PFDs.
‐ If no AP was engaged, lateral and vertical modes disengage. The A/THR, if active, automatically
reverts to (or remains in) SPEED/MACH mode.
‐ If one AP was engaged when FDs are switched OFF, this AP remains engaged in the active
modes but the FDs are no longer displayed.

From the FCOM's here:
DSC-22_30-20 P 7/10

I interpret that to mean that if you switch the F/D's off but leave the A/P engaged, there is still an interaction between what you do on the FCU and the managed guidance. Therefore, if you pull for open descent OR negative V/S, the DES mode will engage.

If the A/P is not engaged AND the F/D's are off then it will stay in whatever phase you were in i.e. CRZ.

Therefore to keep the predictions you would need to already be in the DES phase before switching the F/D's off or switch the F/D's back on, pull for open descent and then switch the F/D's back off.

More easily, just use your mental maths for descent planning if the F/D's are off.

FIS.

[Black_Dawn]

I looked through my documentation and I've come to the conclusion as stated by you FIS.

You mast have the FD's on to interact with the FMS, otherwise the FMS remain in the last phase before the FD's were switched off.

Thanks for your input FIS:)

B_D

[Last Ditch]

My guess is..
FMS will change phase as long as you input into FCU with either..
1. AP + FD On (normal lazy).
2. AP Off, FD On (hands on, using FD).
3. AP On, FD Off (no thrust mode, only speed mode)

With both AP + FD Off, how can FMS predict anything:confused: . Hence no change over and no hockey sticks. I would prefer removing A/Th as well in such a situation. If reqd re-engage A/Th once you commence approach.

Will check the next time around.

Ah one more thing, in such a situation, might as well get into App Phase as early in descend, coz Des Phase serves no purpose.

[Black_Dawn]

Ah one more thing, in such a situation, might as well get into App Phase as early in descend

Yes Last Ditch, is what we did it eventually.:ok:

B_D

[CONF iture]

After a while, during descent and less than 180nm from our destination, we realized that the FMS mode was still in CRUISE phase.
...
My question is: must we have the FD's on, for the FMS to change its flight phase, or what?

Would it be possible that when you did initiate your descent, the distance to DEST was more than 200 NM ?
In such case, the system would not activate the descent phase.
As now your distance was within 200 NM when you noticed the CRZ phase was still active, the procedure would be to enter your passing CRZ FL on the PROG page, and the descent phase should activate.

IMO it is not a question of AP/FD ON/OFF.

[Black_Dawn]

originally posted by CONF iture
Would it be possible that when you did initiate your descent, the distance to DEST was more than 200 NM ?
In such case, the system would not activate the descent phase.
As now your distance was within 200 NM when you noticed the CRZ phase was still active, the procedure would be to enter your passing CRZ FL on the PROG page, and the descent phase should activate.

IMO it is not a question of AP/FD ON/OFF.

We tried that, we changed the flight level in the PROG page, to no avail.
I really think that AP and/or FD ON, are the only way to make the FMS do its "duty".

B_D

[TyroPicard]

I think the FMGS can only provide predictions when you have an AP/FD mode engaged. With automatics off (and therefore selected speed also) there is no requirement for any guidance... so you don't get any.

e.g from FCOM 4 ..... Note: The ND does not display the TOD hockey stick when HDG (or TRACK) mode is engaged.

So with no modes at all you will get even less!

Phase switching to DES requires "initiating descent" (FMGS Operational principles chapter) ..... when you fly raw data you just alter the pitch attitude, you do not "initiate descent" in FMGS-speak.

[Microburst2002]

When hand flying a descent it is better to activate approach (with speed selected). Then you have the magenta donut as a reference, which is all u need, if anything.

I wonder if, afer having done that, changin CRZ level will activate DES phase or what.

Anothr question: what happens if you manually capture crz altitude (ive done it but I dont remember) does CLB phase remain?

[Black_Dawn]

Microburst2002

We did a climb with only the FD's on (A/P OFF) and I remember that levelling off the FMA annunciated ALT CRZ and so the FMS went in the CRZ phase (as I stated in the first post). After the level off we decided to switch off the FD's.
So i wouldn't be surprised (after what has been said in all these posts), that if we would have also switched off the FD's, during climb, the FMS would have remained in the CLB phase even after the level off.

What I've really learned is that the ALT SELECT Knob, with AP and FD's OFF, has no effect on the FMS:* and (as stated before) even changing the altitude in the mcdu, has no effect on the FMS flight phase.

B_D