Thanks chaps - I had no idea of the exact definition of a CDA or indeed what constituted level flight in this context. This info may be buried away in the UK AIP but as far as I am aware is not contained in my company's flight guide (jeppesen).
Ideally, a CDA should be flown at a reasonably constant descent rate, although this will reduce as aircraft groundspeed reduces. Descent from initial CDA altitude is started at a time the pilot judges best with that in mind. In practise, at my home A/F (LGW) the controllers do this for us by giving the clearance to descend at the point for a 3deg (300ft/nm) descent angle. I should say that I always took it that descent rate (in this context) having been cleared, was up to me - even if it involved less than 500ft/min. An intermediate level-off should not be necessary, the most likely cause for this would probably be when a pilot, having initiated the descent, then engaged a profile or VNAV pitch mode. If then the A/C was significantly below the FMC computed descent profile it might level off in an attempt to regain it. Using FMC generated descent paths for CDA's is not normally a sensible option in a radar environment because the FMC may not have the accurate horizontal tracks required to calculate the descent. Good old fashioned mental arithmetic usually works better! Alternatively, and I find this to sometimes be the case, the controller 'finds' some extra track miles during the descent - so 25 miles from FL80 becomes, say, 29. This might require a reduction in vertical speed when the pilot cottons on, but I would not imagine a level-off. Interesting that you feel it is Airmanship to inform the controller in such a case though, and I will take this on board.
Just out of interest, can you guys 'sense' a competent (incompetent?!) pilot simply from his/her 'radar ' behaviour and from what you hear? I am not sure if you will know what I am getting at, but I reckon I can 'sense' a competent controller (as, I know you all are!). Over to you.
Best Regards