Many thanks to everybody who replied to my question.
The matter raised when I flew in London area and was descending with 500fpm. Then captain told me that this is wrong and I should use 1000fpm ( 500fpm when in hold). I referred him to the Jeppesen manual where it says in London area the minimum is 500fpm. He said that it is not correct and in ANO somewhere there is 1000fpm figure is mentioned. It looks like ANO and Jeppesen is in conflict.
From the ATC point of view what is the legal requirements? What about other areas? I didn't see in the Jeppesen anything mentioned about other countries.
I think the 500fpm helps to ATC to identify the aircraft as descending or climbing on the screen. And it is used in TCAS to display descending/climbing traffic. So that the reason to use 500fpm as the minimum.
