speed control

[van der vart]

hi all,

can someone please tell me where i can find information about speed control? i'm looking for something on the net. any good websites?

thank you

[radar707]

Hi,

You won't find a better source of reference than the combined knowledge of the many controllers worldwide who post on this forum.

What do you want to know?

There are certain legal speed limits, other than that speed control is applied at the discretion of the controller (especially in the approach environment).

Ask away and I'm sure all your questions will be answered :D :D :D

[Spuds McKenzie]

van der vart,

Go ahead.

[NW1]

Speed control in the UK is all detailed in the ANO (Rule 23 of the Rules of the Air within the ANO).

CAP 393 - The ANO (http://www.caa.co.uk/docs/33/CAP393.PDF)

The AIM is published by the US FAA here. (http://www2.faa.gov/atpubs/AIM/index.htm)

Hope this helps.

[FWA NATCA]

You can also find information on speed control with the Air Traffic Controllers Book 7110.65N that should be available on the FAA.gov web site.

Mike

[van der vart]

thanks guys

Radar707, i have a lot of questions.
my first is if two aircraft are descending and are passing different levels, speed imposed will not work, am i correct?

and i can't find the materials i wanted on the websites above.

[Findo]

van der ... you are correct. Using anything but Mach number with aircraft at different levels is a waste of time and sometimes positively dangerous.

I'd like to know if you do find any useful info.

[Lon More]

Taking a case you may be familiar with; inbounds EHAM from the North at high levels.

The Letter of agreement between LvlNl (Luchtverkeersleiding Nederland) and Eurocontrol requires that the traffic be at FL260 at the FIR bdy. (22n.m. N of EEL). In practice FL 260 at EEL is acceptable until it gets really busy at ARTIP.

The ACC prefers the traffic in trail so the clearance is often, " Descend FL260, level at EEL, when within range IAS 290 knots."
Please note "Descend FL260," NOT "Descend 260," which, in high traffic, greatly increases the pucker factor.

The speeds can then be adjusted as they approach EEL to ensure the 5 miles separation.
Sometimes flights are transferred on parallel headings, with differing speeds, which ensures the 5n.m. is rapidly ensured

In the descent, vertical rates are often used, where two same type aircraft are on top of each other, the one deemed to be second will be dropped first, with a rate and speed limitation

At other times traffic may be requested to keep up the speed in the descent. This also means an earlier start to the descent, but an earlier arrival at EEL.


Hope that this was understandable after a traditional Christmas dinner. If you are an aviation professional a visit to the Centre at Maastricht can always be arranged, it's much easier to demonstrate it than explain it.

Prettige Kerst verder, met vriendelijke groeten

Lon More,
Here since before Pontius was a Pilot or Mortus was a Rigger

[StillDark&Hungry]

vdv


if two aircraft are descending and are passing different levels, speed imposed will not work, am i correct?



The speed restriction imposed will work - the result, though, could be unexpected!
I know, from experience, that just by giving 2 aircraft the same descent speed does not mean that they no longer require radar monitoring. However, there are a few tricks that we've all picked up along the way to make speed control more effective.

First let me point out that I'm talking purely from an area control point of view using speed control down to about FL150, and bear in mind that it's not my aim to put a stream of aircraft all exactly 5 miles in trail (our MATS pt 2 doesn't allow that for silent handovers)

When I'm teaching speed control, these are the gems to pass on;
Never try to make a gap from nothing using only speed control, you'll need more airspace than you've got! Maintaining a gap using speed control is far easier.
If 1 of your restricted aircraft starts the descent, tell the other one to start to! (as you rightly say - seen to many times an earlier descender has been chomped by the 1 behind both doing 250kts)
Give the required speed as early as possible, in this modern era we are overloaded with level restrictions that aircrew need to take into account when planning their profiles.
If you have it, use some leeway ie. if your aircraft are 10 miles in trail give the first a descent speed of "300 or better" and the second "280 or less" following the above rules should then work a treat!
Finally, look what's happening ahead - again too many times have I seen my fellow ATCO's do some wonderful streaming using vast ranges of speed only for all the aircraft concerned to end up flying in circles round the hold for 20 minutes! beautiful but pointless!

Once again let me say that I'm on the Area side of things, the terminal and approach guys may have a different viewpoint.

Just as an add on - not sure I fully agree with a previous comment about "using anything but a mach No. with aircraft at different levels is a waste of time" I feel that the only time you are guaranteed success using mach number restrictions is if the aircraft are at the same level.

[van der vart]

what if two aircraft are 10 nm apart, the leading say at level 190,
the second at level 280, and i want to maintain the 10 nm spacing.
will 300kts and 280kts on descend work considering the level difference?

[FWA NATCA]

Van Der,

I don't work enroute but at an approach control.

If I have two acft, both descending and being vectored for an approach and lets say that acft #1 is descending through 110 at 210 kts (ground speed) to 40, and acft two checks on at 140 doing about 320 kts, and I currently have approximately 10 miles spacing between them that I want to maintain.

I will have acft two reduce speed to 210 kts (acft #1 speed), then descend and maintain an altitude. When acft #2 reduces to 210 (and yes it takes a few miles) the pilot will then descend to the issued altitude and I should maintain the 10 miles spacing or fairly close to it. Now if acft #2 takes his sweet time slowing up then I will have to take other action but the end result will be to maintain or regain the needed spacing.

Mike
NATCA FWA

[West Coast]

Slow to 210 and a descent is going to yield a pretty slow descent rate, even with the boards hanging out. All this is made even worse if the wings and cowl anti ice is operating. It can be done of course, just don't expect us to come out of the sky like a brick.

[StillDark&Hungry]

vdv

With reference to your last example - the simple answer is no, it won't work! I'm afraid to say I can't give you a simple mathematical equation to say why, because of all the variables. (No-one's mentioned wind speeds yet! Oops there we go!)

In the situation you gave you would have to use an additional form of separation until you had the 2 aircraft at similar levels.
I know it slightly contradicts what I said in my previous post, but if the aircraft in your example were, say, 5 miles apart it may be prudent to make the higher one number 1, and let them overtake. ie. 250kts @ FL190 is not hugely restrictive in level flight, give the 2nd a late descent from FL280 and, depending on type, obviously, they could easily give 310kts+, so with a difference of 60+ IAS, and the altitude difference you could get quite a quick pass especially with a bit of fancy vectoring!

Remember, as West Coast rightly points out, asking a plane to "Go down & Slow down" at the same time, without notice, may cause some frowns on the flightdeck:( :(
Use Newton's laws;) the aircraft at FL280 has a hell of a lot more potential energy - may be easier to use it than waste it:ok:

I'm getting into this:) keep 'em coming.

[BOAC]

van der... are you a controller? If so, it might be an idea for us to put some typical descent mach/IAS numbers on this thread for you?

You COULD then dictate something like 'maintain 0.74 to 300 kts' or similar when really necessary which would cover the problem for aircraft that are not too dissimilar, although I fancy SDH has a more practical solution!

[StillDark&Hungry]

vdv

Went back to the scope after my last post and was able to glean the perfect example for you, 2 aircraft following the same track about 30 miles in trail. The first, obviously early, requested an early 250kt descent - the second was unrestricted.
At FL190 the first was still indicating 250 and was showing a
Ground speed of 345. At about the same time the second was passing FL280 so, when asked, gave an IAS of 310kts which showed on radar as a Ground speed of 485 :ok:

[055166k]

First rule....know your aircraft and their capabilities. There is no second rule; however there is a rule of thumb that has served me well for some considerable time /// 2% per thousand feet will give a rough guide to the relationship between indicated airspeed and True airspeed. e.g. 250 knots indicated at 20,000feet will give 350 knots True [ 20x2=40, add 40%]. 250 knots at 30,000feet will give 400 knots True [ 30x2=60, add 60%]. With heavy jets I have found that they will comply with a speed restriction in knots from quite a high level as long as it is not ridiculous e.g. 300 knots indicated at FL290, which would be about 475 knots True. Obviously not all aircraft can do this and for streaming you may need speeds of about 280/270 until you're in thicker air, say FL270 and below. Difficult to teach so I never use it with trainees, and it isn't exactly written in the manual either. Recommend some flightdeck trips or just try it a couple of times.....or dare I say...chat with the pilots if workload and traffic permits....they seem like nice people!

[van der vart]

thank you very much for the replies.

more comments are very welcome.
would like more materials on the net. i still could not find it.

[055166k]

Sorry ....me again. If you want to slow traffic you will be amazed how slow they can go; a heavy has no trouble coming back to 250 knots, and sometimes they ask for it to avoid excessive holding or ground/stand congestion. They can come back further to 230 or even 220.....but you risk disrupting traffic flow due catch-up.....whatever you do please don't abuse the helpful pilot.....at reduced speed he may need a lot of miles to get the height off and will not thank you for a last minute dive to make a late level instruction......in other words plan well ahead and do not forget to look behind for what is coming next.

[Philthy]

Further to previous posts, pegging Mach Nos is the same as pegging IAS - they will only be the same at the same level.

If the aircraft are at different levels, then you need to think in terms of TAS (of course, you don't use TAS with the aircraft). And that's to say nothing on the effects of wind gradient!

[Jerricho]

Just for my 2 cents worth Van,

Don't ever forget that aircraft can't slow down well and go down well at the same time..........especially if there is a tight level requirement for whatever reason (airspace, holding facility). You'll really endeer yourself with an instruction to a jet cruising at 280ish knots at FL200 "Reduce speed 220 kts and descend FL130".................throw in an expidite request and see what happens! ;).

Also, as has been mentioned here by SD&H, I have seen some brilliant efforts at streaming jets 5 mile in trail, with the first guy screaching along at +300kts to be told he'll have to hold. Through no fault of the pilot, seen some great hold entry procedures from some poor guy trying to wash off nearly 100 kts in speed.

All the best,

[Lon More]

throw in an expidite request and see what happens!

Controller then requests, "Use your speedbrakes."

Pilot answers,"They're for my mistakes, not yours."



Lon More
Here before Pontius was a Pilot or Mortus was a Rigger

[van der vart]

so just to confirm, if both aircraft told to fly 250kts, the one at higher level is actually still faster than the one at a lower level?

minimum clean speed = no flaps, no speed brakes = minimum cruise speed?

[Lon More]

so just to confirm, if both aircraft told to fly 250kts, the one at higher level is actually still faster than the one at a lower level?

Yes

minimum clean speed = no flaps, no speed brakes = minimum cruise speed?

Should be lower, can't remember off-hand as I don't think I ever used it; it should be laid down in the aircraft manual - Vmin.m? - if it's become this desperate, I'd want the stall horn blaring :uhoh:

[PhilMac]

If all else fails, turn left, turn right etc usually works, and if we take 'em off the STAR, - please explain is required. An arriving plane usually slows down quicker when it is not pointing at the airport.:ok:

[ILS 119.5]

I agree with "know your a/c" all modern day a/c can reduce speed if required but only to a certain limit before the use of flaps etc. Down under a/c are told to reduce speed by the flow controller many miles away from the destination for sequencing. I don't know if this is the same in the USA. In the UK in an area environment a/c can also be told to reduce speed at high levels but will only do so if the a/c can comply. In an approach environment a/c can reduce/increase speed if the speeds are within the envelope. Outside this the captain will not comply. It is really up to the controller to know what a/c can comply with any speed control which may be required. "Speedbird Concorde 1, reduce speed to 140kts", "Sorry cannot decrese below 210kts at this stage", "Roger", "Midland001, (F100), decrease speed to 140kts", "Roger wilco, can do 130kts if required". Its all up to knowing what the a/c performance is. Mainly aqquired from experience.

[van der vart]

ma again.

if an aircraft at FL370 which we want it to be fast and given descent speed 310+,and one at FL270 told to maintain descent speed 280kts.
am i correct in saying that the aircraft will only pick up speed (310 kts)when it starts descending and passes say FL290?

i was given the impression that an aircraft is quicker at higher level!

thank you

[Miles Magister]

Van de Vart

Yes you are basically correct. You need to sit down with someone who is good at big sums to understand it properly but your best speed will be around FL290 to FL320. Below that your true speed will again decrease.

[eyeinthesky]

Van Der Vart:

Some good info so far, but you need to get clear in your head the relationship between Mach No, Indicated Airspeed and Ground Speed.

1) Ground speed: Self explanatory, and it is affected by headwinds/tailwinds and the airspeed of the aircraft.

2) Indicated airspeed: In the scenarios you are describing, it is the number of knots shown on the Air Speed indicator and is, in simple terms, the speed of the air past the aircraft. At lower levels (say FL280 and below) it is this that aircraft refer to and it is this which is the limiting reference.

3) Mach No: This is the speed of the aircraft in relation to the speed of sound. (Mach 1 being the speed of sound). At higher levels, it is the mach no which becomes the reference and the limiting factor. Because of the changes in air pressure and density at higher levels, the indicated airspeed in knots actually reduces for a constant mach no as an aircraft climbs. Therefore, and aircraft which is doing M0.84 at high level might have an IAS of only 250 kts or so but a True Airspeed of 490 kts and a groundspeed around that, depending upon winds. If you like, the reason the IAS is lower is that there are less molecules of air per second going past the aircraft for the instrument to measure, because the air is less dense.

Where all this becomes relevant to ATCOs is in the application of the theory. If you ask an aircraft to maintain an indicated airspeed all the way from FL350 to FL 180 you will find that his speed over the ground (ignoring wind) will reduce considerably. This is because he will by choice be using a MACH NO to, say, FL270 and then an indicated airspeed which is often the maximum permissible. For a 737 the mach no might be M0.74 which might equate to 250 kts IAS, but gradually as he descends into thicker air the IAS will rise towards 310kts, whilst the Mach no remains constant. Thus, if you limit him to 250 kts from high level you will find him doing 60 kts less than you might expect.

The easiest way to use speed control is to specify a mach no and then "When able, IAS of 300kts" (or whatever you want). As others have said, Speed control will not CREATE separation, but will MAINTAIN it.

[055166k]

Get yourself a decent flight simulator program and fly a couple of planes....pay particular attention to all the parameters that are the cause of your concerns!