Hi Hong Kong Phooey. I think it is you that is full of it. For some basic sequencing facts...... Two aircraft 10 miles apart out on the cruise in the mid 300s flight level wise, if descending from say 100-110nm with a slow down to 250 knots 10-13000 feet on the arrival will see you need a 20 knot indicated diffference from the time they transition to the indicated speeds as the guy in front willl be around 2000ft below and for every 2000ft, you need 10 knots indicated of difference just to match the ground speeds plus the extra 10 knots to account for the ground speed slow down as they approach the star constraint of 250 knots and even then you willl physically have to pull the back aircraft to 250 knots about 15nm from the height/speed constraint point. That is to just keep to 10 miles. Now, at about 60 to touch down, with matched ground speeds to have 5nm at touch down, you need 10.2-10.4nm between the aircraft if you are going to use 230 knots at about 30, 210 at about 15 then allow (instruct) them to slow to the same speed on final. We do this day in and day out and while Hong kong is not somewhere I have worked, I am assuming the laws of physics work the same there. Interestinglly I have flown in there up the front and there are some seriously track mile chewing arrivals and the ATC use lots of short cuts on them to secuence.
So from the above, If you have a beautiful line of aircraft out in the cruise all exactly 10 miles apart to just keep that during the descent, first one comes down at 320, 300, 280, 260 and everyone gets slowed to 250 at the arrival point, 15, 30 and 45 miles away from it all in a big consateena. Throw a fifth aircraft into that and we have holding/vectoring. Four aircraft five miles apart in the cruise is two too many and will require some air traffic control to be inflicted. For example, the same scenario I used above, for each additional 10 knots of indicated difference, you will gain about a mile. To dumb it down, front guy at 310 knots, second guy at 290 knots keeps your gap, if they are 7 miles apart, you need an additional 30 knots to get your 10 so the back guy comes down at 260 knots. Throw another 30 into that and now we have serious delays. If you can force the aircraft to transition onto indicated (ie descend early) at about 140 miles, 30 knots will give you 10 miles from a dead heat (ie 310v280). This is all pure speed control, hands off ATC. I personally prefer to make you all go flat out, get down fast and stick you into a holding pattern where I can drive the speeds and the distances to actuallly make you get to where you need to be when we mant you as opposed to some lax interpretation of it.
edited to add, the above is pure speed control to keep SPACING as opposed to speed control to achieve a cross point@time scenario.
Last edited by Plazbot; 27th Mar 2012 at 09:32.