The principle of "don't ask them to go down AND slow down" is understood by most ATCOs but it can still be overlooked at times. Expediting descent is in one sense the opposite of this, as speed and rate-of-descent are inevitably interlinked.
I believe there is a good point worth mentioning here and
GMWTB touches on it in his post above.
If the need for a high rate of descent can be foreseen (e.g. after crossing opposite direction traffic) and we are warned, then we can prepare for it by reducing speed to min CRZ and then, when the descent clearance is given, a much higher rate of descent can be provided to fit the "plan" by increasing back to normal speed (or greater) to facilitate a higher rate of descent. We will then achieve the lower level more quickly - but maybe with an increased forward speed. In other words, if you can pre-warn us of an expedited descent and/or accept a higher forward speed on arrival at the lower level together with the necessary space for the subsequent speed reduction, then much greater flexibility is possible. Our, options of course become much more limited once flap extension has started on the approach.
Basically, it's all about conversion of P.E. into K.E.
JD
