Had a good one the other day. We had been cleared to a level, to be level at a certain point. So we started our descent. Then we were told to change our cleared level to a higher one and bring our speed back. Then we waited a good few minutes until we were told once again to descend and make that FL by the same point. At the time we were probably about 5 miles from the point and, oh, about 8,000 feet higher than the level restriction. We suggested to ATC at the time that it was rather unlikely we were going to make it!!
Goldfish Watcher, I am more than happy for an "expedite through FL XX". Not a problem. In the machine I fly we can choose to increase the speed to increase the rate of descent or we can give you a fixed vertical speed (ie. rate of descent), XXXX feet per minute.
The only problem for this lies in the speed. If you tell us to expedite AND reduce speed or if we are limited to say 250 knots and we're still pretty high we can't increase the rate of descent much more. We try and descend with power right back, at idle, so the only way to increase the descent is to put the nose down, which means an increase in speed, if only temporarily.
Wow, does that make any sense at all?!!