You were the one who said (Post 41) you didn't necessarily understand operations in other sectors...
Indeed I was and this is completely correct. There are at least 60 sectors in the UK, of which I work 7, and I do have a detailed knowledge of sectors surrounding mine, and I have a basic knowledge of the sectors beyond them. But that probably accounts for maybe 30% of the UK. There is simply no requirement for me to have any kind of knowledge about the rest, as nothing I can do will affect them. Therefore it is true to say I don't
necessarily understand, that would depend on which sector is being referred to. The post I was responding to didn't make clear which sector or route he was talking about.
IAS can well be above 270 at higher altitudes
And it's no problem if it is. I assigned him 270kts or less. If he was flying faster than 270kts then I would expect him to slow down to 270kts (or less) and comply with the restriction. If he can't then I would expect him to tell me he is unable (with a genuine reason) and I would change the plan.
My (and I am unusual) main concern with ATC speeds are unrealistically high speeds required at lower FLs, particularly "increase speed" instructions. These cost a lot of fuel, and given we still fly in random directions / hold, achieve nothing!
Fair enough, I can understand how annoying that must be. I can think of a few reasons why that would happen, though none of them excuse it:
- The controller gets caught off guard when the aircraft descends at anything less than say around 270kts from high level. Of course we don't know what speed you'll be flying when you convert, and the vast majority of airlines fly at or faster than this (in an A320 series a/c). We usually only apply speed control if we have less than approx. 12 miles in trail, and we may have a lot more than this (20+ miles) at high level. 20 or even 30 miles will very quickly erode if you fly at say 250kts and you are in front, and that may prompt an increase speed instruction (but would normally be more last minute when a large catch up is apparent). If the first a/c is doing 250kts for economy, and the second is doing 300kts for speed, we may give both 275kts as a compromise. The problem at this point is the first a/c is low on profile and the second is high on profile, therefore both a/c have wasted a lot of fuel compared to if they had known the speeds before commencing descent and were able to plan accordingly.
- The other main scenario would be when you are cruising at say FL240 and there is higher descending traffic for the same destination/STAR fairly close behind who has no chance of overtaking you without some speed manipulation. Either we slow down (to facilitate an overtake), or we speed up the aircraft at FL240. The problem here is that applying the same speed will still not provide enough separation because of the level difference. The closer the a/c are, the bigger the difference will need to be (If we had 15 miles we could probably give both a/c 270kts, because we could allow a catch up to begin while there is a large level difference - the speed difference will become much less as the 2nd a/c becomes much closer vertically to the front a/c). If we only had 7 miles we'd need similar groundspeeds immediately, so something more like 300kts for the front a/c and 270kts for the back a/c would be needed to account for the large level difference. The situation is made far worse when the back a/c are transferred already high on profile and therefore need the higher speed to make the level restriction. I hope that makes sense, quite difficult to try to put into words.
There is absolutely no requirement to do so and you shouldn't really need to, but you are most welcome to tell us what speed you are planning on when you call us in the cruise. This saves anyone getting caught out and will obviously save you fuel. Until controllers/the airspace design changes to accomodate the more economical speeds being flown, this is the only short term solution I can think of at the moment to this problem.