As it was a "
when ready descend " clearance, and the a/c didn't vacate for about 20nm, the speed/level-by problem should not apply. If this
was the case, then the pilot
certainly should inform us of the 'not able to comply' with an
executive instruction, be it either level-by or speed.
NW1, I think that the phrase used was, without doubt, the correct one to use, as speed
when able means just that and not when you want to. The phrase you suggest would give the exact problem we have here, whereby some decide to stay on Mach number until passing say FL200 giving a huge IAS to reduce from, rather than switching around FL300 when 280kts is acheivable.
Other threads recently (and not so) have banged on about wordage for speed control, and the one used is direct and unambiguous, the other ones used are :-
"
when you switch to indicated" - gives the problem highlighted above.
"
on passing FL280, IAS ***kts" - the one we are supposed to use, but we're not pilots and too many times get response, "can't do that until FL***" Too much RT. Also some are already doing 300kts+ by this level, and thats unwanted.
"
descend FL***, IAS ***kts" - response, "not able that speed at the moment". We do know that, but its the speed we want acheived, but again this phrase can get unwanted replies.
"
descend FL***, make the speed transition 280kts and maintain for descent" - have only ever used this twice, first response "eh?????", second was unpleasant as I got the impression he thought I knew/was attempting too much, and we also don't know the handling of every aircraft on every different day.
Its a difficult battle to get speed control affected, and the RT guidelines poor. One day someone will come out with the knockout phrase that combats every problem, and ICAO hopefully snap it up immediately, lets just hope its soon
