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?
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.
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 . 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.
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.
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".
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.
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.