Why do some pilots consider speed control to be optional??

[PSR]

Hi there,

I am an area controller in the UK and I have a question for pilots. This has begun to annoy me now as it seems to be happening more and more. I give a pilot a speed to fly and the pilot ignores the instruction. Either he/she doesn't fly the speed at all, or they choose to comply at a point that suits them etc. Heading/level instructions are not optional. Nor is speed control, so why do some pilots continually refuse to fly the assigned speed??

I am aware that if aircraft are not given descent early enough then they may be unable to comply with level restrictions and speed control at the same time. I always make allowances for this by informing the pilot which constraint to comply with first (I know there are plenty of controllers out there that don't and then moan about it afterwards when the pilot is unable to do as requested).

The scenario I had today was a very short haul flight (B734) cruising at FL170 and had been cleared when ready to FL130. I asked the pilot his speed, he said 320kts. A few minutes later I asked him to slow to 300kts, which was readback correctly. 5 minutes later the aircraft is still showing the same groundspeed and is catching up the aircraft in front (hence giving the speed restriction in the first place), so I checked the mode S which still said 320kts! I queried this with the pilot, to which he said he was planning on 300kts for the descent. He then reduced his speed and separation between him and the aircraft in front was not lost.

Perhaps I am missing something here, but to me there seems little room for confusion. In this scenario all that resulted was it increased my workload, clogged up the RT even more, and the pilot was still stuck behind the aircraft in front of him so achieved nothing by ignoring the restriction.

I know the vast majority of pilots comply with the speeds that have been assigned, but the few that don't really do increase our workload considerably as we have to issue more instructions (headings, stop descents etc) to achieve exactly the same result.

Perhaps someone can shed some light on this from the point of view of pilots.

[Dream Land]

My own opinion is that this is an airmanship issue, experienced crews will smartly adjust speed when within 30 DME.

[Capt Pit Bull]

Unfortunately a small but significant percentage of flight crew are obsessed about maintaining high speed and direct routings even when the situation clearly doesn't favour it.

Obviously impossible to comment on this example without seeing an exact transcript of the RT. (and maybe the cvr!)

But broadly you might want to prepare yourself for the fact that if you say anything remotely ambiguous it will, by this small percentage, be interpreted as faster / more direct. When it comes to descent and speed reduction, you could do worse then add the word 'now' even if strictly speaking it is not required by standard RT.

(standard rt could probably do with an overhaul in regards to descent and speed control, but I've been saying this for years).

[dhardesthard]

I totally agree with you that the pilot should immediately comply with the instruction to slow down. The only thing that I can think of is that the pilot thinks that you may not notice him closing in on the preceding A/C and hopes to get away with cheating. He is probably looking at the conflicting A/C on his TCAS and doing his "own thing". Suggest you throw in the phrase "Immediate speed reduction required". Good luck.

[dhardesthard]

If the controller did not want you to reduce speed immediately he would say so. Where did 30 DME come from? Would one apply your 30 DME rule to a heading change?

[PENKO]

The only reason I have observed (I'm being very diplomatic here) for pilots to be reluctant to slow down is when they perceive themselves as being high on profile.

Pilots hate being high and hate speed brakes even more so they use increased speed to correct the situation. Being told to slow down means they will end up even higher on profile, definitely needing the speedbrakes, so they temptation to cheat a little is very great, especially since a speed reduction is not well defined: I can slow down from 320 to 250 in twenty seconds, but I can also do it in 2 minutes...

This is in no way an excuse:ok:

[Kingfisher]

If separation is compromised a couple of laps round the hold should cure the problem. You have to be cruel to be kind

[Lord Spandex Masher]

PSR,

Professionalism, The lack of.

[Defruiter]

It's just as bad in the approach environment too, and it's only getting worse. I may as well be banging my head against a brick wall the majority of the time. (It also annoys me that a lot of pilots also fail to read back the speed instructions. It's a mandatory read back just like heading and level instructions!)

[Fly26]

I think some people are pressured to make up time and feel pushing the limits a bit shaves off a few minutes here and there...I think the lack of speed control in other countries by ATC allows crews to take advantage...therefore discipline after a long day when entering back into say London Airspace sometimes lapses. its a shame...poor discipline and wanting to get home.

[heloguy412]

A long in the tooth pilot once told me, "ATC is advisory only.":E

[judge.oversteer]

Yes, PSR, good post.
Have to admit that I have done that lots of the time, especially speed control regarding flap/auw with the B744, ie 230/235 kts or 180/185 kts.
Headings; no, not really, depends on the wind.
Sorry but...
Ciao.

Ps. sorry PSR, just realised your post pertained to Area Control, but my comments are stil valid.

[quarefellah]

Hi All,
While we are on the subject, can someone please clarify the situation w.r.t. speed increase instructions. I understood that ATC were not permitted to INSTRUCT a speed increase but rather could only REQUEST one. I find this practice common in certain European FIRs but notably not the UK.
Also I was given to understand that (UK) controllers expect a speed reduction to be made at a rate of 1kt/sec. Is that correct and where is the reference?

[theshed]

As i fly very often in the UK on short haul trips in a 734 I can only say sorry.

But I must admit anytime i'm in the aircraft speed instructions have and would be complied with.

Perhaps it was a simple mistake. :uhoh:

In my company for the most part we try to make your lives as easy as we can especially as, lets face it you guys can make a Jersey as short or as long as you like for us......

;)

[PSR]

Theshed, that's very good of you to say and is much appreciated. It may well have been a simple mistake. We all make mistakes afterall so I can hardly condemn anyone for that.

That said, it's really just an example to highlight what we regularly see from other airlines.

[ZeBedie]

I don't think there's much scope for discussion - you're given a speed - you fly it. If controllers start MORing the offenders then maybe things will improve? I hope they do because I don't want to share the sky with people who choose not to comply with their clearance.

And I think the original complaint was posted in the right place because many people would have missed it in the ATC forum.

[Basil]

Worth repeating:
No matter what trainers, captains, managers say; speedbrakes are not a cosmetic enhancement. When necessary, use them!

[The Ancient Geek]

I don't think there's much scope for discussion - you're given a speed - you fly it.


In most cases yes.
But Harare approach can yell at me as many times as he wants to maintain 210 knots, it was never going to happen in a Twotter.

[eagerbeaver1]

Maybe they forgot? Maybe they were very tired, maybe they got distracted. Maybe it was the second sector of a six sector day - late already. There could be many reasons.

We could all offer mitigating arguments.

I just did as was told, I didn't have the radar screen and couldn't see the bigger picture.

NATS are the finest ATC in the world.

[Exascot]

There is no excuse if he read back correctly.

"ATC is advisory only."

My wife is a retired ATCO, can I quote you on that because I always obey? Well mostly :E

[GlueBall]

I concur with judge.oversteer that large heavy a/c have speed/flaps issues, which is to say that having to manoeuvre with flaps extended in order to comply with a slower speed multiplies fuel burn, and after a 14 hrs flight there isn't much "extra" fuel to be dragging flaps.

There is no excuse for non compliance, but controllers should also be conscious of performance constraints when ordering a 747 to reduce to 220kts when 50 miles out. :ooh:

[MrHorgy]

Rocketing around at 320 kts at FL170? What's to be achieved with this on such a short sector? You'd save one minute at most probably, which you might lose if you were given delaying vectors... :ugh:

[Trim Stab]

I expect I'll get flamed for this - but when asked to slow down we try to comply as tardily as we think we can get away with (similarly, when asked to descend too early for optimum profile).

Margins are so tight in corporate flying at the moment - the only profit we make per flight is what fuel we can save compared to that budgeted on the flight plan. In our company we are desperately trying to keep the company afloat and keep our jobs - so if we can save 50lbs of fuel, we'll fight for it.

If you think somebody is taking the mickey, just say the magic words - "slow to xxxknots, or expect a hold at yyyy"!

[NigelOnDraft]

I make all efforts to adhere to ATC speed requests. However, I do wish sometimes ATC understood:

Being asked to speed up to >300K in the same sentance as "expect 10-15mins delays" is just asking my employer to tear up £50 notes in quick succession.
Asking someone, from level flight, at say 270K as requested, to lose 10,000' in 25NM, with a tailwind is just not going to work.
Asking us, directly or indirectly, to break the TCAS V/S limits is going to be refused.
I will refuse to go >270K in turbulence if I judge it unsafe, or even unnecessarily uncomfortable.I appreciate pilots will have different speeds they wish to fly - but I think ATC have some responsibility towards the planet and not burning fuel totally unnecessarily ;)

[RomeoTangoFoxtrotMike]

[ Disclaimer: I am not a pilot or ATC ]

Surely, if the circumstances described by NoD, or others, apply, the pilot should respond "Unable" and hopefully add "due [reason]" as soon as possible, to give the controller an opportunity to come up with a new plan, rather than silently disregarding, and making him and everyone else guess... ? :hmm:

[DBate]

I concur with judge.oversteer that large heavy a/c have speed/flaps issues, which is to say that having to manoeuvre with flaps extended in order to comply with a slower speed multiplies fuel burn, and after a 14 hrs flight there isn't much "extra" fuel to be dragging flaps.

There is no excuse for non compliance, but controllers should also be conscious of performance constraints when ordering a 747 to reduce to 220kts when 50 miles out. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/icon25.gifAll correct, however there is no reason - when given a reduction to 220kt by ATC - not to ask ATC if you may 'maintain 230kt to stay clean'. In my experiance that request is usually granted unless the controller really needs you slower.

Point is, if a specific speed intruction is given, then we are to comply. Airspace nowadays, especially in Europe, is way too crowded. Instructions by ATC are given for a reason, and usually it's not just 'for kicks', but to avoid coming close to other traffic or for flow control. The whole system is at times operating at its limits, so lets not make our colleagues work on the ground (i.e. ATC) harder than it already is by not complying with instructions.

There is no room for 'personal interpretation' of a clearance. If you have doubts, then ask for clarification. My guess is that this is way more preferable than just doing what you think ATC wants you to do.

And regarding use of speedbrakes; it's a paid part of the aircraft. Why not use it when necessary.

[PSR]

The majority of my colleagues are aware of the difficulties speed restrictions can impose on flight crew (with regard to descent profile, turbulence, tail winds etc.) and try to take this into account. There is obviously, however, a vast difference in performance between aircraft types flying in/out of the UK, and we simply don't have enough detailed knowledge about every type of aircraft and what the pilot can/can't do with it. Therefore, the logic most people seem to use is to ask for what would be easiest and if the pilot is unable then he/she will say so (and most pilots seem to). Then we can sort out something different. This happens regularly when asking for level and speed restrictions at the same time etc.

Obviously there are different objectives the flight crew are trying to achieve in each aircraft (whether it be to save as much fuel as possible, or get to destination as quickly as possible), but when the airspace is busy everybody has to fit into it safely, and this will mean you could be assigned a speed of anything between 250 and 320kts typically to ensure aircraft remain safely separated. If you are unable to reasonably comply with the restriction imposed, then please say so. That is aftera ll what we'd expect you to do.

[con-pilot]

To be honest, I never gave speed assignments much thought. What ever was requested I did*. Now for speed reduction, I just used the throttles, not the speed brakes.

As the old saying goes, the speed brakes are for my mistakes, not the ATCs mistakes.

* Unless I believe that an assigned speed was unsafe for the conditions; faster or slower. Which rarely occurred.

[Sussex Kestrel]

As a professional you endeavour to do your best with speed constraints- if not, simply speak out- however (though my profile states that I can indeed hover at the drop of a hat) in reality whilst at D7 on the ILS maintaining 180kts (an atc instruction) being asked to maintain 160kts to D4 is, for most jet liners (though especially the 757), a pointless request- especially when in the clag with anti-ice on the go.
The two way understanding between ATC'ers and flight crew has improved over the years through, in my opinion, such liaisons as the latter visiting the former's workplace- seeing it all unravel, as it were. Controllers coming along on flights to see how it is put into practice would only help both communities acquire more of an understanding of both professions.........
Don't get me wrong, most of the controllers (especially at London's Sussex airport) are top class.... :ok:

[Trim Stab]

If we have filed a flight plan, which has been accepted and acknowledged with a stated cruise flight level, how do ATC justify holding us down at a lower level?

On more than one occasion, I have uplifted OPS-minumum fuel for the filed and accepted flight plan, then been held down below the planned flight level for a significant portion of the cruise meaning that we risk not having enough fuel for the flight. The answer is not - "you should have uplifted more fuel" - we fly to extremely tight margins and if fuel is more expensive at departure than arrival, we uplift the OPS minimums.

The whole point of OPS fuel regulation is that it should cover all forecasted eventualities with sufficient safety margin for safety - so how do ATC justify throwing a completely unforecasted spanner into the equation by holding us down below the planned flight level?

[J.O.]

Would you rather receive a 30 minute slot delay to ensure that you get your desired cruise level every day? ATC do the best they can, especially in Europe where there are more planes trying to share the skies than separation normally allows. Besides, unless the ATC are holding you down by an order of 10,000 ft or more, the contingency fuel in your flight plan should more than account for the different altitude. If it doesn't, then it seems to me that an ASR to your company would be a good start at correcting the overly tight fuel planning you're being asked to accept.

BTW, if you're flying in Europe in today's environment, it's pretty hard to say that a lower than planned altitude qualifies as "completely unforecasted".

[Cough]

Trim tab, sorry, no sympathy from me.

Sometimes we are 2000 ft lower, worst I've had recently is 4000ft lower. But the direct routings that ATC provide more than make up for the level (especially from Maastricht!). And if you think about it, to guarantee your level, ATC would have to ensure that a 100nm section of your route is clear for you to climb into (15 min slot window at 400kt) Now that's just plain greedy, but if we went that way, nothing would move due to it's slot!

Min fuel is all very well, but you already know what happens and should ensure your fuel uplift is enough to cover your expected flight, not some theoretical dream...

[NigelOnDraft]

If you are unable to reasonably comply with the restriction imposed, then please say so.There are 2 issues with this. Firstly, the pilot using the R/T often reads back the "clearance" without being able to consider it i.e. the ATCO now thinks the restriction has been accepted.

(S)he now either realises that it is not possible / acceptable / suitable, or more likely, the PF (who really decides if it is) points out it is not possible etc. They will take X seconds to discuss.

Secondly, the R/T is now so busy they cannot get a word in to request / demand / refuse / amend that clearance, and by the time they do, the ATCO has given another aircraft or 2 clearances based on our aircraft's apparently accepted clearance.

I do not know what the solution is? But I do sometimes get the impression ATCOs think we just dial in these numbers (height, speed) and the aircraft just obeys with nil side effects. They do not realise we have *** all fuel, and using speedbrakes, or excessive speed, and then get vectored round the sky / go into the hold makes little sense, and can even be hazardous.

I must add that there are exceptions... and we have been advised of our descent speed / holding duration / descent restrictions 10-20NM prior normal ToD. We can then plan the descent accordingly, request appropriate ToD, and fit in with their speed / altitude / holding profile, whilst keeing things safe, economical & comfortable ;)

[PSR]

Nigelondraft - that's a very good point and something I'll certainly bare in mind. I was always trained to give speed instructions well in advance on TOD to ensure, like you say, that your descent can be planned accordingly, and for the most part I do this (usually only unable to if traffic is bunched and all aircraft arrive at or past TOD at the same time, which happens annoyingly often).

My post wasn't so much referring to these sorts of scenarios. I was thinking more of the occasions when speed instructions are given well in advance of TOD (like with the B734 previously mentioned), but are still ignored.

Another example that springs to mind from 6 months or so ago was a business jet (C750 perhaps?) given a speed restriction of 270kts or less when he was cruising at FL400 and at least 30 miles from TOD. The pilot flew at mach 0.85 (or something similarly high) until FL230! IAS was around 340kts if I remember correctly. His excuse was he hadn't transitioned to IAS yet. This too makes no sense to me. 270kts or less is 270kts or less. It applies at any level, even when flying with reference to mach, simply meaning IAS never greater than 270kts. Perhaps I'm missing something but how can that be misinterpreted?

[PSR]

Trim Stab - filing a flight plan doesn't automatically give you the right to continuous climb up to your filed cruising level. If there is traffic in the way, which there almost always will be at some point, then you may have to level off lower temporarily. CAP493 states any aircraft already at your requested cruise level will get priority over you - that's the rules we work to. In the UK we will do our best to get you to your requested level as soon as possible. The only reason you wouldn't get it is if someone else who is on the same route is there already at that level, or if you've filed to avoid flow restrictions on certain sectors (but even then we'll often let you climb into the sector on an ad hoc basis when we can see what the traffic situation is like and make an informed decision based on that). I know certain other countries in Europe use blanket level caps for specific destinations, but I can only speak for the UK. There will however often be procedures requiring us to present traffic in such a manner to those other countries, preventing us from giving you your filed level. I hope that answers your question.

[Intruder]

I was always trained to give speed instructions well in advance on TOD to ensure, like you say, that your descent can be planned accordingly, and for the most part I do this (usually only unable to if traffic is bunched and all aircraft arrive at or past TOD at the same time, which happens annoyingly often).
Why revert to explicit control "way too late" when all you have to do is tell each aircraft in succession to 'plan to reach WPT at TIMEZ and xxxKIAS'? Then they can figure out how to do that.

I can't understand why there is so much manual manipulation of descent and arrival profiles when there are numerous STARs that have all that speed and altitude profile stuff built in. All that's needed is a time at the beginning of the STAR, and the rest should sort itself out. If that's not working, then have somebody rewrite the STAR so it does what you need it to do! While there may be occasional unplanned conflicts, the STAR should be a 90% solution...

[PSR]

all you have to do is tell each aircraft in succession to 'plan to reach WPT at TIMEZ and xxxKIAS'? Then they can figure out how to do that.

If only it were that easy. Maybe one day it will be that way, but there are so many factors working against us at the moment (air space design, encouraging neighbouring sectors to present traffic, A at a suitable level so that pilots aren't way above profile in the first place, and B to initiate some sort of streaming in advance rather than just transferring everything to us way too late and expecting us to do everything). :ugh:

Unfortunately the routes I'm thinking of are on a political boundary (I guess that wouldn't be much of an issue in the USA) where there is little or no chance or achieving any kind of change for the better, certainly not in any time soon anyway. Until then we'll continue to struggle to make some sort of order out of the chaos, with everyone frustrated that we're asking them to achieve something they can only just, or maybe can't even achieve in the time/distance given. :rolleyes:

[GlueBall]

Trim Stab "If we have filed a flight plan, which has been accepted and acknowledged with a stated cruise flight level, how do ATC justify holding us down at a lower level?"

...The short answer could be that YOUR airplane is not the only one in the sky.:{

[The African Dude]

Hi PSR, interesting discussion, thanks for posting.

given a speed restriction of 270kts or less when he was cruising at FL400 and at least 30 miles from TOD. The pilot flew at mach 0.85 (or something similarly high) until FL230! IAS was around 340kts if I remember correctly. His excuse was he hadn't transitioned to IAS yet. This too makes no sense to me. 270kts or less is 270kts or less. It applies at any level, even when flying with reference to mach

We often receive "Mach xx and xx KT on conversion", so I can see how a tired or otherwise busy pilot could misinterpret the instruction - despite the obvious clarity in your request.

At my UK base we are very limited in descent by a mid-level restriction during arrival which often requires a higher speed down to around FL60 to get below the terminal limits. What a number of us cannot understand is why we are given standard speeds with 2 to 4 thousand to go before we are passed to approach, at which point the speed restriction is removed. (We of course appreciate that there may be other influencing factors that we cannot know of from the flight deck).

AD

[PSR]

AD

That would also be very difficult for me to understand as the design of each bit of airspace in the UK is so different and I only have a detailed understanding of the sectors I work. We do welcome visits by pilots to the centre as it can only be of benefit to all of us. Likewise we do look for opportunities to spend time on the flight deck, which I've managed to do a few times, and I must admit I've found it invaluable.

[Intruder]

given a speed restriction of 270kts or less when he was cruising at FL400 and at least 30 miles from TOD. The pilot flew at mach 0.85 (or something similarly high) until FL230! IAS was around 340kts if I remember correctly. His excuse was he hadn't transitioned to IAS yet. This too makes no sense to me. 270kts or less is 270kts or less. It applies at any level, even when flying with reference to mach
At FL400 M.85 is close to 270KIAS. FL200-250 is generally where the Mach to IAS conversion will take place when doing a normal conversion from M.85 to 310 KIAS or M.82 to 290 KIAS or similar. You need to get your head around the Mach/IAS relation at high altitude.

You also need to learn more about the airspace outside your own little box. If you don't understand your adjacent sectors, how can you provide good ATC "services"?

[Denti]

Switchover between 200 and 250? That is mighty low. We do standard switchover at 295 and FMC switchover is usually higher up to FL360.

From PSR's post he has a grasp of the Mach/IAS concept and of switchovers. The instruction seems quite clear to me, fly whatever mach number you want until you reach an IAS of 270kts and then fly that IAS. Not that hard to grasp and even easier to program into an FMC. Speed control is there to squeeze more of us into a given constant airspace and of course prevents slot restrictions and holdings, it is in our best interest to follow it as we follow every other instruction by ATC. And if we can't "unable" seems to work quite well.

[Intruder]

Switchover altitude depends on the high-altitude Mach number and the low-altitude IAS setting you program into the FMS. Those also vary with the Cost Index you set.

With a low CI, the switchover altitude may be very close to cruise altitude, because the FMS is going to revert to a low IAS (as low as 250 KIAS in the 744) very quickly. With a higher CI, the switchover altitude will be lower. If you manually program a low Mach number and higher IAS (e.g., .80/310), the switchover will be much lower. With a high CI (>250) and left to its own desires, the 744 FMS will program a low-altitude descent of >335KIAS, and will reach it closer to FL 200.

Also, without further direction, it is implied that you will retain your present cruise Mach in the descent until reaching the switchover IAS. Last I knew, the default low-altitude descent speed is 290-310KIAS above 10,000'. There is seldom a "do whatever you want" aspect to it.

[PSR]

On the contrary I do understand my adjacent sectors very well. And you're right, that is absolutely essential in providing a good service.

Perhaps my understanding of the mach/IAS is not quite correct then. My understanding was higher level cruise (depends on a/c type but usually above FL300) was done in mach. Maintain a constant mach during descent (e.g. 0.795), during descent on a constant mach groundspeed will increase slightly as you get lower. IAS, even though not flying with reference to it at higher level, will be fairly low at FL400/M0.795, something like 220kts or maybe less. This will also increase gradually as you descend on a constant mach. Then on reaching a specified IAS (say 290kts) you switch from flying mach to flying IAS. Descent on IAS will then cause groundspeed to decrease as you descend. You maintain that IAS (provided no other factors such as turburlence etc require you to alter it) until reaching lower level where any other procedural speed restrictions may kick in (e.g. 250kts at FL100).

That is my understanding provided there is no intervention from ATC. If it is incorrect then please do say as this is what I use on a daily basis to separated a/c and I would really appreciate further understanding. As Denti explained, my instruction was intentionally issued at high level, and in good time for the pilot to plan a descent at not above 270kts. Since at high level he is highly unlikely to be flying faster than 270kts, the speed restriction wouldn't really kick in until he is at say FL350(ish) (if flying at M0.85 that is approximately where I'd expect it to be). Bare in mind I never asked the pilot his mach number to begin with as I couldn't care less. I just needed him slower below FL300 as he descends and meets other traffic.

[Dream Land]

Within 30 DME of what?
Of the airport, but to make easier for you to comprehend, that will occur when being handled by a TRACON, versus an eroute facility, and the closer I get to the airport, the quicker my response will be.

[NigelOnDraft]

PSR

Your understanding is pretty good and the earlier posts are either showing remarkable lack of basic knowledge, or trying (as your case illustrated) "to cheat the system".

"Switchover" altitude partly depends on atmospheric conditions, but more on what the mach / IAS specified are. In an A320 series, at FL350, if you ask me to slow to min/holding speed, I am effectively flying IAS at FL350.

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!

[Intruder]

On the contrary I do understand my adjacent sectors very well. And you're right, that is absolutely essential in providing a good service.

Perhaps my understanding of the mach/IAS is not quite correct then.
. . .

. . .Since at high level he is highly unlikely to be flying faster than 270kts, the speed restriction wouldn't really kick in until he is at say FL350(ish) (if flying at M0.85 that is approximately where I'd expect it to be). Bare in mind I never asked the pilot his mach number to begin with as I couldn't care less. I just needed him slower below FL300 as he descends and meets other traffic.
You were the one who said (Post 41) you didn't necessarily understand operations in other sectors...

Your understanding is essentially correct, but with a major bad assumption: IAS can well be above 270 at higher altitudes (the 747 frequently will cruise at 310 at M.85), so you SHOULD care about the cruise speed/Mach. If you want a specific speed at a specific altitude, then make it perfectly clear by stating "270 KIAS by FL300"! Otherwise, you will be at the mercy of the current FMS setting and a possibly lower switchover altitude.

[PSR]

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.

[Northbeach]

The scenario I had today was a very short haul flight (B734) cruising at FL170 and had been cleared when ready to FL130. I asked the pilot his speed, he said 320kts. A few minutes later I asked him to slow to 300kts, which was readback correctly. 5 minutes later the aircraft is still showing the same groundspeed and is catching up the aircraft in front (hence giving the speed restriction in the first place), so I checked the mode S which still said 320kts! I queried this with the pilot, to which he said he was planning on 300kts for the descent. He then reduced his speed and separation between him and the aircraft in front was not lost.


I like the discussion about FMC cost index & crossover speeds but.......

You have a 737 at 17,000' indicating 320 KIAS.

You (ATC) tell the flight to slow to 300 KIAS. The flight does not slow to 300 KIAS. 300 seconds pass and you see no change in groundspeed.

Put an end to the nonsense and file a violation against the crew; just make sure that your phraseology was textbook.

By the time the crew gets through all the related tension, pressure, work and expense involved with defending themselves against an alleged violation of aviation regulations they will have wished they had simply complied.

Guaranteed the "news" will spread that XYZ Center/approach darn well means 300 knots when they say 300 knots. Likely one will see company bulletins, online notices and "emphasis items" during line checks (here we go again).

No, you are not being an A**, you are trying to do your job safely with limited airspace. If you do not get cooperation then YOU get to make the decision on initiating certificate action. Was the non-compliance out of misunderstanding or arrogance? If it was arrogance; then file the violation.

I think the vast overwhelming majority of us try and comply with every clearance every time recognizing we work with fellow professionals.

[GlueBall]

PSR ...keep in mind that B747 will burn less fuel being vectored extra distance for separation at zero flap speed, rather than having to slow down "way out" and dragging flaps. Zero flap speed upon arrival could typically be around 220kts. :ok:

[seat 0A]

Yeah! Let's drag 'em into court!
Good point Northbeach :ugh:

[Sky Wave]

Got to agree with Penko's post. If you've planned on a certain speed for decent and then get asked to slow down it will put you high on profile and some pilots hate using speed brakes. Personally I just advise that I'm unable to make the restriction, however as NOD says it can sometimes take a while to get a word in edgeways. Secondly as someone else pointed out, jet aircraft don't go and slow down. If you allow it to do a little bit of both it will take a while to reduce speed.

The biggest time that I'm guilty of not adhering to ATC assigned speeds is the 160 to 4d request. The aircraft simply will not slow down without dropping the gear. Very often it ends up being 170ish in which case I'll drop the gear at 6 miles and be reducing through 150 by 4 miles. (basically too fast for the first couple of miles and too slow for the last couple of miles). Not strictly correctly but I believe it evens out correctly. The alternative is drop the gear when requested, p**sing away loads of fuel and making lots of noise. Of course if the speed is ridiculous I will drop the gear early.

Standing by for abuse :)

[PukinDog]

Trim Stab...If we have filed a flight plan, which has been accepted and acknowledged with a stated cruise flight level, how do ATC justify holding us down at a lower level?

On more than one occasion, I have uplifted OPS-minumum fuel for the filed and accepted flight plan, then been held down below the planned flight level for a significant portion of the cruise meaning that we risk not having enough fuel for the flight. The answer is not - "you should have uplifted more fuel" - we fly to extremely tight margins and if fuel is more expensive at departure than arrival, we uplift the OPS minimums.

The whole point of OPS fuel regulation is that it should cover all forecasted eventualities with sufficient safety margin for safety - so how do ATC justify throwing a completely unforecasted spanner into the equation by holding us down below the planned flight level?How does ATC "justify" it? How can anyone who flies not know the answer is "traffic"?

If your "extremely tight margins" don't allow you to "hope for the best, plan for the worst", it calls into question the viability of the operation itself. If saving 50 lbs of fuel is going to make or break the company then the real concern is how such a shoe-string operation can afford far more costly and more critical things like maintaining the aircraft to a safe standard or hiring experienced pilots who understand the difference between theory and reality when it comes to flight planning.

In the future, you should apply real-world aviation experience to your operation's fuel-figuring and (that's right) uplift more fuel. It sounds like the policy (or the person driving that policy) itself is flawed or not well-versed enough if it/they ignore the world of ATC delays/changes etc. They are as much a fact of aviation life as dynamic/unforecast weather situations, blocked runways, State aircraft showing up, aircraft in distress, etc, etc that can force delays that require more fuel than what your planning program includes. A couple bingo-fuel diversions in a year will blow any teacup-fuel savings you think you're realizing by flying around in a potential pan-state all the time.

In the meantime, unless you've stated to the controller you can't accept a speed/altitude assignment or its been given at pilot's discretion, you're obligated to comply promptly, not "as tardily as you think you can get away with". Your faulty planning or erroneously thinking yourself unique in the cause to save fuel/money for your operation does not justify unprofessional behaviour in the cockpit.

[EngineOut]

My experience is that when flying to the UK the workload is always higher than when flying anywhere else in Europe. This is mainly due to ATC. As a relatively new FO it's hard to know what to "usually" expect from ATC the first couple of times when flying to a new destination. Never flown the whole STAR into any UK aerodrome.. ATC trying to get the most out of the airspace increases the workload on the flight crew making them more prone to mistakes.

Sometimes winds, weights and icing conditions make it pretty hard to lose speed/altitude.

[Doug E Style]

Re. the speed issue; nobody has mentioned the fact that on the Airbus in managed descent mode, the speed will sometimes vary a bit (if the winds are different to those forecast/entered) in order to stay on the correct descent profile. Our SOPs state (and common sense suggests) that selected speed should be used if ATC have assigned a descent speed but that doesn't stop some pilots (who think they know better) to leave it in managed rather than use the speed brakes.

[sultangc]

That happened to me a couple of time. After I received and speed reduction instruction , I followed that as required, but wind was from calm to tail or front to calm, during descent, so my IAS was 20 kts less as required by ATC control, but my GS was still the same one. Sorry, as ATC Control please asked for another reduction for another 20 or more kts. This could be what happened to you.