Codie and interesting point; what is a profile?
QF762s at 320Kts used to be closer to QF763s than they are at 300Kts due to the (bypass issues, I think that was it) different engines...
The latest management/saftey experts wanted everything flying same; so now 300Kts all around... effect 762s are slow and low, like the good old days.
To achieve a landing rate with like types, (jets) 744's, 734's and 763's and 738's (at 290kts, if they stay high) very similar profiles at 300Kts, (speed over the ground) (excluding internationals) 737's, 738's (virgin), 712's similar, but 712's can be a little slippery and require extra watching...
As for the other jets, Inter 744's (who knows how they will go, usually Singapore are slippery, MAS also, but Thia, United, BA, Cathay are all slower, sometimes crazilly so... but then every now and then you get a fast one that really stuffs everything up...
Giving speeds is only one aspect; a 340Kts Thia that is low, goes slower over the ground (because of the height factor) than a QF738 at 290kts, generally speaking.
Then you throw in a mix of others like Ba146s, which everyone thinks are slow, they are till they point the nose down; then gravity takes care of it... high descent profile + less IAS, equals more Ground Speed than many give them credit for or in some cases plan for...
Then business jets etc... other internationals 772s, 773s, DC10s, MD11s, A342's, B763's, B743's, B742's etc... None of you do the same thing... Eventhough most of you are flying 300IAS...
Approach want you to be nicely spaced, 250Kts below 10; this evens things out remarkedly... You are all very similar below 10... but how you get there keeps me employed...
MAESTRO only knows what the engineers told it; most jets all do the same time from 120 miles... all jets... awsure! This is why we get you all slowing down and then turning etc... Because MAESTRO picked the wrong number one... MAESTRO is Strategic time based flow; the ATC's are the tactical element.
As for giving the 'times at a fix'; which we call the feeder fix (FF); WELSH, RIVET etc. two times 3 minutes apart might have two aircraft at 120SY at the same time; because of different FMS settings, crew input etc. Aircraft A chooses min mach, 300kts on the drop; Aircraft B chooses normal mach, 250kts on the drop. both at 120SY together, aircraft A will get to the Feeder fix first, but not with a sep standard. Also times are constant... landing rate might be 2.5 minutes, how do you issue that...? Crew can be +/- a minutes of the time issued etc.
If it were as easy as giving out times; we'd all get a lot more done... but in practice that just doesn't work. When people try, it gets really ugly, fast...
I've been caught with turbo props the most; number one on an FF; I'll slow everything else to 210Kts and space them; 10 miles apart; then number one is doing 180 but doesn't speed up at the FF; all of a sudden, the trail is gobbling him up at 60kts G/S... ugly... number one, report speed, 180kts, not speeding up until descent... well that won't work... speed from the FF means just that... even if it does take effort.
Jets at 250 and t/p's at 210 from 45 SY is almost the same time from 45 SY to the threashold, due different circuits, turning times etc. hence why these were chosen. BN and ML are also using these, to keep things consistent...
Bottle of Rum.