A320 : how change ALT CRZ in ALT
 

Hello,

Last flight during turbulence, unable to descend below due to traffic.
Some variations of speed due to the mode "SOFT ALT" (+/- 150ft) engaged by the "ALT CRZ" FMA mode.

I was unable to switch back in "ALT" by changing the level in CRZ FL page PROG.

Any idea ?

Thank you

The Soft Altitude function on the A320 is only +/- 50ft (DSC 22-30-70-70 p2-4).

My first guess would be since the ALT CRZ was already captured, changing the MCDU to a new cruise ALT is not affecting the current mode. To enable a return to ALT only, I suspect you could set VS+0, then type the new CRZ ALT in the MCDU, then reselect the current level with the FCU. It should get back to capture the current altitude with ALT only. Be careful though as to verify the actual ALT blue on FMA! :ok:

Alternately just wind the FCU to 100 feet above your current altitude, VS +100 ft / minute and when the aircraft goes to CLB mode you can alter the FMGC CRZ LVL before returning the FCU to the original ALT and VS back to that level. The whole thing can be done in +/- 50 ft. Just be vigilant with your FMA's to make sure you are back in ALT mode at the end of it all.

There are so many mod states now that all combinations on the FMA are achievable in the cruise phase with or without MCDU PROG FL the same as the FCU selected one.
Identification of being in or out of "soft" or "hard" alt is now difficult if you fly a mix of MSNs,FMS1 or 2,FMGS supplier, CPIPS fit etc etc.
Best way to be in control of the aircraft in turbulence is to use fixed manual thrust and push for speed mode on fcu and SELECT a speed slightly higher than @1/2 way between upper and lower barbers poles.
nb. Dont nip to the loo with manual thrust set:ok:
This way you dont get the +/-50' of the aircraft in soft alt mode which can make the back of the aircraft VERY nasty, esp in an A321.
You will have noted that generally REC MAX alt in an A320 is FL391, to allow for +/- 50' variations in the cruise but some have a REC MAX of FL394 and some have FL398! Go figure?:confused:

Did you try putting a fl above your current fl on the prog page? Putting a fl below obviously wouldn't work.

Don't you trust your effo? :}

Soft altitude mode freezes the N1 for passenger comfort.
Selecting the speed around to "wake up" the thrust normally does the job.

According to the maintenance manual, if i recall correctly, push to level off is not exactly a V/S zero mode, but an ALT mode. If this is correct you can use it for a while.

But you can just introduce a higher CRZ ALT, then initiate a climb, then inmediately go back to level, then ATL should come active.

And, let's not forget the golden rules. If the airplane is not doing what you want, and you don't like what the A/THR is doing, disconnect without fear.

Hi charlies angel,

it is a matter of certification actually, having the airplane certified up to FL398 is quite useful in metric operations where you can accept some higher levels in meters. I guess this has been done to promotes airplane sales in countries operating with metric reference.

Cheers.

Pull selected speed and set to Fly on IAS.

The soft alt only works when flying in Mach mode.

I-2021
That makes sense
TVM:)