Airbus Cruise Level Change Close to TOD

[piper mohawk]

A question for Airbus drivers.

You are in the cruise phase at FL350 and you are cleared by ATC to descend to FL340 because it's smoother down there. You are about 40 miles from the calculated TOD indicator on the ND. SPD HDG and ALT are in managed mode. What is the correct way to change cruise level?

Select FL340 on the FCU and PUSH the ALT knob
Select FL340 on the FCU and PULL the ALT knob;
Use V/S mode;
Enter a new cruise level in the MCDU;
Some other way.

My reason for asking:

How does the aircraft know that you are commanding a lower flight level and not initiating the descent phase?
Hope this makes sense!

Tailwinds...

[Flightlevel001]

If only descending 1000', most of us would probably try to do this in a gentle manner. You could push for managed descent; if you haven't yet reached TOD the autopilot will only demand a 1000fpm ROD. Personally, I'd probably do it in V/S between 500-1000fpm ROD up at that level. The aircraft will have entered the descent phase so if you want to revert to the cruise phase, you can simply enter the new level into the MCDU, however, at only 40 miles from TOD, it wouldn't really make much difference. Different airline's SOPs might dictate a certain way of doing it, but mine doesn't - just a bit of airmanship ;) Doing the above in OP DES would be a bit enthusiastic I might suggest, as it will command the autothrust to flight idle, only to be brought back up again seconds later after a short 'plummet'!

[FlightDetent]

1) set FL 340 on FCU (that needs to be done in all cases)
2a: the V/S method) select V/S -500 or -700 and pull the VS knob
2b: the DES method) push the alt-sel knob, commanding a managed 1000 fpm descent
3) read the FMA and have your colleague verify
4) insert the new CRZ FL value into the PROG page.

4 is only a cherry-on-top option if you need to keep things super neat. Completely unnecessary with only 40 NM to TOD. Beyond 100 miles, the machine would do so automatically.

[piper mohawk]

Nice one - that all makes much more sense!
Thanks.