- V/S is for reducing what a managed or open climb/ descent will give you.
- it's also for targeting a rate from ATC I.e. We're level at FL390 and ATC ask us to descend to FL300 and be level in 6 minutes. Easiest way is VS -1500. A managed descent below the profile on the A320 will only give 1000 FPM and an open descent will give a high rate.
- ATC in places like Germany often ask for a rate of descent I.e. 'minimum 1500 FPM'
- Different ICAO states have different minimum rates of descent. E.g. The ICAO standard is 1000 FPM hence the reason the A320 gives a minimum 1000 FPM in a managed descent. However the UK only has a minimum rate of 500 FPM so we can halve our rate until on profile and thus be 'commercial'.
- VS is very useful for controlling a CDA around an approach. It's far more accurate for achieving a 'glide star, loc star, super star'.
- VS is helpful to stabilise the rate through a turbulent level on climb in my opinion.
- VS as has been mentioned is a controlled way of approaching a level to avoid a TCAS TA or RA. Something some Ryanair pilots could do with learning. I've only ever had them from them. I'm sure they are the exception not the rule.