Unless it has changed recently, I understand the definition of a CDA to be:
No level flight for longer than 2.5nm below 6000'
Therefore a V/S of -100'/min falls within this definition.
At our base we are often held high then have to dive down at the last minute to get under the G/S, making a CDA less than easy to achieve.
As for the Captain getting annoyed, there is rarely a good reason for this, but it might have been:
1. He was annoyed at ATC/late cabin secure call/etc, not you.
2. Your flight selections were innappropriate for some reason*
3. He was having a bad day.
4. He has a problem with you for whatever reason (unlikely).
4. He is a ****/control freak (much less likely these days).
*Ask him in the crew room "Was there anything about my approach you would have done differently?"
When I brief an arrival, we both know our base wants CDAs, so that bit is taken as read. However, what I usually say at the end of any brief is "I will follow SOPs but if I have missed something or am beyond any limits, just remind me - I won't be offended".
That last bit is the duty of PM of course, but even so; saying this tells the other guy that you won't bite their head off or get moody, and they almost always reply "yeah, same goes for me too" So now you both know that you are both open to appropriate comments and are going to have a good day.
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