I tried to explain a while back - in Europe, (my area) 'Descend xxx', when queried, is often found to be 'at pilot's discretion'; I am reluctant to point at any particular countries, but there are a few where this is more often than not the case when a 'early' descent clearance is given for no APPARENT reason, and nearly always for some inter-area hand-over agreement. This is NOT a 'pop' at ATC, but an attempt, as I judge from other posts, to reduce R/T loading (OK - pilot generated!), and does NOT refer to UK ATC. The only criticism there is a systemic one where the descent 'restrictions' are sometimes 'known' only to the controller.
I think from all the posts, NorthernSky's (6/8) sums it up best:
"As pilots, we want to stay at cruise altitude and descend with the ideal profile.
All of the above debate seems to spring from one annoyance: If ATC give us a descent instruction, in the form 'Descend FL330', we reply, 'Roger descend FL330, is that pilot's discretion?, and ATC say 'Affirm, that's when ready'... then we're not being provided the SERVICE that we should be, in the first place.
In a nutshell, the controller should ALWAYS specify 'when ready' when it applies. Not to do so costs us money.
Because they don't, we ask. If they did, we wouldn't ask. "
It is because there are quite a few who do not say 'when ready' when it is relevant. I have NO issue with your NEEDING me to descend. I will. Maybe it is a training thing in those areas where it happens more? It appears that ALL ATC people on this thread DO say 'when ready' where it can be given. Good. The problem lies with those who don't.
It SHOULD be abundantly clear to all pilots reading this thread that 'DESCEND XXX' means now. That is what I have always assumed it to mean. It is just that after a few hundred descents where it was not necessary THEN, we become a bit inquisitive!
Can I also take it from the lack of comment that 500fpm is OK with ATC for an 'early' descent (unless other rates specified)?
The original thread post raised another issue - that of pilot awareness of/ and interaction with/ FMC programmes. There is an obvious gap there in the way the FMC works v the ATC 'picture' of what we will do, and we need to close that gap.