I am trying to find out more about the required minimum rate of descend. I found a reference in the UK AIP ENR 1.1 -> 3.2.2.3 which states the minimum as 500ft/min below which a pilot has to inform ATC. I looked up few other AIPs and found nothing alike yet every once in a while I hear from pilots about this rule. Is there any ICAO document (or else?) that might be a base to such minimum?
PS. I found this thread but it doesn't answer the question:
http://www.pprune.org/archive/index.php/t-304997.html
Thanks