Maintaining Rate Of Climb

[pilotnik]

Hey guys, I would like to ask you a major question I have been struggling with for a long time. I happen to work on both sides of the radio (ATCO low & high ACC + B737) hence I don't know if it is only me who see the problem or am just overreacting.

Let me do a small intro into the issue. ATC use vertical speeds for a variety of reasons like separations, putting aircraft into proper sectors, sequencing - that is understood. A great deal of these rate restrictions are given in the mid ACC airspace, where aircraft are not yet on STAR but already descending or they already left SID, but still climbing. That part of airspace is usually less organized than the TMA, as the routes guiding traffic towards the STAR entry gate and from SID exit are often intersected by other routes. Different FIRs may of course have different ideas on mid and high level traffic management but I think we can all agree that mid and high level instructions to keep rate of climb happen.

Having said that, I would like to ask what do you think about instructing aircraft to maintain a particular rate of climb in a a situation when that aircraft is in it's late-climb, like climbing through FL320 up to FL380 for example? All ATCOs know the basic principles of flight so we know that we all need to take aircraft performance limitations into considerations when instructing to keep certain RoC. What readback do you usually expect from the pilot in that situation? And if there is a pilot reading this, what do you think the ATCO is thinking when giving this instruction? Do you know what is the limit for your aircraft on that flight and what is the maximum rate and for how long you can keep it?

Thank You

[eckhard]

Please excuse the obvious answer: “it depends”.

Generally, most airliners should be capable of 1000 to 500fpm ROC at medium levels.

If ATC needed more, they would of course ask. Sometimes it’s difficult for the pilot to predict accurately the achievable average ROC over a large height change. Personally, I tend to respond with an under-estimate.

Some light jets, like early Citations, struggle a bit above FL350. If I can’t maintain 500fpm I will ask ATC for a slow climb of 100-200fpm. In the medium levels even a Citation should be able to give 1000 to 500fpm.

[The Many Tentacles]

As an ATCO working anything above the TMA levels, dependent on the sector I'm doing at the time, if I want a rate of climb I'll either ask if you can manage it or I'll pick something that I think is reasonable. If I'm asking an A321 to give me 2000ft per minute for 5 minutes I know I'm going to be disappointed , hell I'd probably be disappointed if I asked for half that rate of climb :} If I need a rate of climb I'll often overestimate anyway to give myself a safety margin. I'm also aware that the higher you go, the less chance I've got of getting an expeditious rate of climb. I hate the phrase "good rate" as I always tell my trainers that your version of good could and often does differ considerably from the pilot's one, but that's a different rant. If we give you a rate of climb/descent, it means that we've built in our separation which saying good rate doesn't offer us.

Give the choice, I'd rather use level by a point as then the whole thing is up to you guys

[wiedehopf]

High rate of climb is not good for the engines life span. Run them cool.
My machine can have full climb, climb 1 and climb 2. We are instructed to use climb 2 when ever possible subject to safety issues.


The differences in climb power derate settings above 25000 ft are not that big or so I've heard.

Also there is a point where the True Airspeed is reducing in the climb somewhere around FL330 i believe. The climb rate above that point can be better than below depending on the case.

Maybe just ask if they are able to do XYZ and if they say yes follow up with the instruction.
That way they know they will probably level off if unable and can decide engine wear and other considerations for themselves.
Optimally they will say "unable" or "i'd have to check first" even with the instruction but it's not a given.

[Great Charmer]

Sorry for the intrusion, did there used to be (or maybe there still is) a 500ft minimum climb/descent requirement to fly in UK controlled airspace. Or am I dreaming that.

[Bobermo]

High rate of climb is not good for the engines life span. Run them cool.

My machine can have full climb, climb 1 and climb 2. We are instructed to use climb 2 when ever possible subject to safety issues.


What type is “your machine”? Most jets that I know of will have only 1 climb thrust setting above FL160-FL220..

[Bobermo]

So if you don’t change it and you selected CLB 2 before takeoff it will keep CLB 2 until the climb to cruise level is completed?

On the 737 once you’ve passed FL160 there is no difference between climb thrusts anymore and only CLB remains.

[parishiltons]

There is a problem (well several, really) with ATC specifying a rate of climb. Doing so is in effect specifying the solution to a problem on someone else's turf (the pilot's), whereas the aircraft operator will likely come up with a better solution. If ATC needs an aircraft to be at a certain height by a time or place they should tell that to the pilot, who can then work out the best way to achieve it, rather than ATC doing the solutioneering for the pilot. Most ATC have a good appreciation of what an aircraft is capable of doing performance-wise, so should tend to give instructions accordingly. If in doubt ask - 'can you reach FLnnn by time/place/next x track miles', or even 'what is your best rate of climb?' etc.

Factors to be considered include not only the performance capabilities of the aircraft, but cost, weather, environment, passenger comfort, fuel burn/endurance, etc. etc. These are for the pilot to work out, not ATC. I advocate that ATC specifying a specific rate of climb/descent, unless it is for the purpose of reducing cumbersome step climbs/descents in a non-surveillance environment is really poor technique.

[qwerty2]

Sorry for the intrusion, did there used to be (or maybe there still is) a 500ft minimum climb/descent requirement to fly in UK controlled airspace. Or am I dreaming that.


No dream. It's still in the Enroute Section of the AIP.

[zonoma]

parishiltons:
I advocate that ATC specifying a specific rate of climb/descent, unless it is for the purpose of reducing cumbersome step climbs/descents in a non-surveillance environment is really poor technique.
What about in a radar environment then, what would you suggest? Not every sector is blessed with 60nm+ of lateral playground, the inevitable getting a short haul B738 underneath the long haul A343 sometimes is unavoidable, I just tell the B738 to stick at 500'/min to keep it comfy. There are always exceptions.

[pilotnik]

OK so it is safe to say that this knowledge is well established. The general rule is that the higher the aircraft is the less we can expect from it. ATCOs anwers from this thread sound exactly the same to those from my FIR. Of course, if you ask 20 ATCOs „what is the max rate you’d give to an a/c climbing through FL340”, you would get a wide spread of answers, somehere between 500fpm and 1500fpm. Every answer is based on ones experience and hence very subjective. There is no hard rule like „above FL300” you must not instruct over 1000fpm or whatever - this would be very restrictive. If I am flying with small gross weight and in addition I have high speed I could easily do 3000fpm for a longer time, even at higher levels. On the other day, with high mass and low cost index (IAS ~ 240) I would have to turn on the APU to gain 800fpm at best! But that is not what I have a problem with. I am more curious about how is this possible that pilots tend to answer positively that they are able to do a certain rate when the only thing that they are basing their confirmation on is... their intuition. Some of you may go ballistic upon reading this but that is the truth! ATCOs don’t even realise that a pilot have absolutely no way of telling what rate she/he can maintain and for how long. There is no instrument for that. Moreover, there is no way to tell if the temperature will not increase in a couple of seconds or if a tailwind will not strenghten! And if that happens, your ROC falls faster than a crewmember o a bed after red-eye flight!
What pilots do is that when the rate falls below the limit they start reducing speed. They move the energy from lateral speed to vertical speed. Of course there is a limit and at some point you just can’t keep reducing any more and you say „unable”, when the traffic you are being separeted from is only 10 miles away. That is the moment when panic vectors usually kick in. I never give hard rates to high level aircraft but I hear my colleagues do and you can always hear one of the two answers, either acknowledgement or „we will try”, which basically means „I have no idea”. I am telling you, maybe 1 in 20 pilots is self-confident enough to say „negative” when not 100% sure that she/he can deliver. I have seen how this looks on both sides of the radio and both sides are unaware what happens on the other side in such situation. Now, if you think that this only pertains to some crazy, badly educated pilots or ATCOs from wherever the hell you might imagine, than no! I’ve took part in one investigation with a „pink” airline crew who misjudged their performance when asked to do „only” 800fpm, and my colleague had the same with „yellow-blue”, where both pilots were let go after the TCAS they induced.
In my opinion in these severe situations crews are only half to blame. It is true they confirmed the given rate without hesitation and then didn’t do it, but it was the ATCO who asked for it. Maybe pilots didn’t realise that ATCO have no idea what it takes from an aircraft to climb faster. Guys, ATCOs have no idea that you can’t add more power to increase vertical speed! Most of us think that it’s as easy as that - you just push the throttle.

Now go ahead! Jump on me! I said what I had to! :}

[parishiltons]

parishiltons:

What about in a radar environment then, what would you suggest? Not every sector is blessed with 60nm+ of lateral playground, the inevitable getting a short haul B738 underneath the long haul A343 sometimes is unavoidable, I just tell the B738 to stick at 500'/min to keep it comfy. There are always exceptions.
Not sure whether you are referring to getting a 738 down through the level of 343 (don't see many A340s anymore!) or whether you are stuck with the 738 under the other one wanting a higher rate of climb? In the former case I'd give the 738 a requirement to be at a level beneath the 343 by a time/place/distance that assures vert sep before you lose lateral/longitudinal. In the latter case unless you have room to vector then I would just tell the 738 that there is slow climbing traffic above as the reason for being stuck at an assigned level vertically below for a while. In both cases it lets the pilot work out how to achieve the solution in the best way, rather than imposing a performance specification that might not be possible. The rate of climb technique lacks built in separation assurance (pilotnik's post above highlights some of the issues) and certainly has to be constantly monitored - a task you don't want when already busy.

[ATCO1962]

I'm not sure why a controller would presume to know anything about a particular aircraft's climb performance at high altitude. We have no way of knowing the aircraft's weight, it's engine performance or any restrictions to such engines, unexpected temperatures at altitude, etc, etc. With all the bells and whistles up the front, just ask the pilot what s/he can give you and you will have a pretty good idea as to what you can expect. Anything else you give is just a hopeful guess on your part.

[The Many Tentacles]

We'll take best guess. That's why we always build in more separation than we need

[mikk_13]

In Germany we use rate of climb as it is faster than measuring and the instruction is shorter. Due to the volume of traffic we simply don't have enough time to let pilots fly .

We mostly use the mode s Mach number and aircraft type to 'estimate' the next 3-4000 feet of performance ie a321 at m.73 @fl330 will be bad.

It is really important if crews tell us before if the rate is not possible or ask if they are cleared from f280 to f370 at a rate how long they need it if in doubt .

To be honest it also depends on the operator aswell, many of the colleagues will not run tight separation with some but are happy to do it with others. Regardless of all the polital issues, Ryan air crews are very reliable and thus we are usually willing to run things a bit tighter than some of the wetlease charter airlines .

I find the attitude of 'no rates stay of the cockpit' that some have posted here as a bit 'old'. Sorry but if you want that then prepare to fly 8000 below requested or be vectored all around the sky (not likely because it takes time we don't have).

Happy to answer questions about how we do it in central Europe land :)

[pilotnik]

In Germany we use rate of climb as it is faster than measuring and the instruction is shorter. Due to the volume of traffic we simply don't have enough time to let pilots fly .

We mostly use the mode s Mach number and aircraft type to 'estimate' the next 3-4000 feet of performance ie a321 at m.73 @fl330 will be bad.

It is really important if crews tell us before if the rate is not possible or ask if they are cleared from f280 to f370 at a rate how long they need it if in doubt .

To be honest it also depends on the operator aswell, many of the colleagues will not run tight separation with some but are happy to do it with others. Regardless of all the polital issues, Ryan air crews are very reliable and thus we are usually willing to run things a bit tighter than some of the wetlease charter airlines .

I find the attitude of 'no rates stay of the cockpit' that some have posted here as a bit 'old'. Sorry but if you want that then prepare to fly 8000 below requested or be vectored all around the sky (not likely because it takes time we don't have).

Happy to answer questions about how we do it in central Europe land :)

Do you rely on crews confirmation that they are able to do a particular rate? This example you gave with FL280 up to FL370 - if Ryanair crew confirms that they are able, do you take their word for it and if the aircraft is in fact not able to maintain the rate you just consider it only their fault or both you and the crew?

Do you have any statistics in Germany that say which crews are more reliable than others? Actually the more precise question would have to be: Do you have any statistics on which crews are better in foreseeing the future? There is no doubt that there are better and worse educated pilots, exactly as there are better and worse educated ATCOs, but linking education / english level / skill with ability to tell what rate can be maintained in 8 minutes is a major failure in understanding the concept of aircraft energy management.

I am also surprised to hear that not giving high level rates have anything to do with "old fashioned" air traffic control. In my opinion it is the other way around. The more you get aware of how the jet aircraft works the less overconfident you get in ATCO job. On high altitudes jets are really flying somewhat on the edge of their potential. If anything should be called old fashioned it is not understanding what vertical speed is about and how it is connected to temperature, wind, IAS and thrust.

Now, you touched a very important case about using Mode S to estimate whether an aircraft can keep high rate or not. You can easily use IAS for this purpose and this is a single best predictor of what the aircraft is capable of. Unfortunately it is only good until a certain level and in my opinion an ATCO is not able to tell where the limit is, as the minimum IAS is depending on the mass - still it's quite good. Be that as it may, even though crew knows exactly what the mass and IAS is, there is still absolutely no 100% sure way to predict the rate in 5 minutes. I would like to learn more on the German way of doing things though! You wrote that you estimate the performance capability by looking at the actual Mach number? Can you explain this mechanism? Is it only you who are doing this in Germany or everybody does this?

Oh! And using this occasion on which we are distinguishing better pilots from worse, let me tell you that it is among others Germany and France where some ATCOs don't even understand the concept of Mode S Mach number indication... I am telling you that you can find unprofessional staff in every company. There is less of them in companies with well established HR policy but you can be more than sure that even in RYR, DLH, AFR there are black sheeps. Now, the more you trust the "professionals" the more you are exposed to the one "unprofessional" pilot who will do a blinking red mess out of your screen.

[mikk_13]

Do you rely on crews confirmation that they are able to do a particular rate? This example you gave with FL280 up to FL370 - if Ryanair crew confirms that they are able, do you take their word for it and if the aircraft is in fact not able to maintain the rate you just consider it only their fault or both you and the crew?

Do you have any statistics in Germany that say which crews are more reliable than others? Actually the more precise question would have to be: Do you have any statistics on which crews are better in foreseeing the future? There is no doubt that there are better and worse educated pilots, exactly as there are better and worse educated ATCOs, but linking education / english level / skill with ability to tell what rate can be maintained in 8 minutes is a major failure in understanding the concept of aircraft energy management.

I am also surprised to hear that not giving high level rates have anything to do with "old fashioned" air traffic control. In my opinion it is the other way around. The more you get aware of how the jet aircraft works the less overconfident you get in ATCO job. On high altitudes jets are really flying somewhat on the edge of their potential. If anything should be called old fashioned it is not understanding what vertical speed is about and how it is connected to temperature, wind, IAS and thrust.

Now, you touched a very important case about using Mode S to estimate whether an aircraft can keep high rate or not. You can easily use IAS for this purpose and this is a single best predictor of what the aircraft is capable of. Unfortunately it is only good until a certain level and in my opinion an ATCO is not able to tell where the limit is, as the minimum IAS is depending on the mass - still it's quite good. Be that as it may, even though crew knows exactly what the mass and IAS is, there is still absolutely no 100% sure way to predict the rate in 5 minutes. I would like to learn more on the German way of doing things though! You wrote that you estimate the performance capability by looking at the actual Mach number? Can you explain this mechanism? Is it only you who are doing this in Germany or everybody does this?

Oh! And using this occasion on which we are distinguishing better pilots from worse, let me tell you that it is among others Germany and France where some ATCOs don't even understand the concept of Mode S Mach number indication... I am telling you that you can find unprofessional staff in every company. There is less of them in companies with well established HR policy but you can be more than sure that even in RYR, DLH, AFR there are black sheeps. Now, the more you trust the "professionals" the more you are exposed to the one "unprofessional" pilot who will do a blinking red mess out of your screen.

thanks for the questions.
1. Yes we expect the crew to inform us when they can not maintain an assigned rate. Obviously if they do not maintain an assigned rate and do not inform us that they must reduce, then there will be some issues.
2. It is my experience and oppinion. I work a lot shifts, work with many controllers and speak to many acft. Unfortunately some opperators are much less reliable than others. Just listen to the frequency for the 3 missed calls for one frequency change. It is possible it is a failure to monitor the energy state, not to predict it.
3. All of the issues regarding performance are well understood, however we are often climbing acft above multiple crossing flights. Therefore an average rate is not possible (conflicting flights are at multiple levels) and the clearance takes too long to transmit and readback. For climb with rate at pilots discretion would require vectors are multiple flights, which means you would have to cut them off well below cruising level for quite some time.
4. We can see the mach via mode s. It gives a feeling of the possible performance for the 3-4000 based on acft type and destination. It is faster for us to click and check than ask. I can't say which units have mode s,but I know Maastricht have it. For example I know an a320 climbing at m.78 can easily keep 1000` pm for the next 3000 feet of climb through level 280. I also know not to try much abiive 360 with an a320, esp when speed is .74 or less.
5. Absolutley. You won't find me ever trying to expedite anything with a crew that doesn't give me a good impression (like answering when I call). On the other side I have seen some controllers make some interesting clearances. Often colegues will give a clearance then add `due traffic` on the end. It is an extra hint to crews that they better pay attention to what's going on.

We are always working with a plan b incase the rate is not able to be maintained. However this plan b relies on the crews reporting that they are unable to comply with the clearance. We also can observe the rate via mode s which is very accurate when compared to mode c calculations. The updates are frequent and therefore we can monitor the entire situation with quite a high degree of accuracy.

I would also suggest that for most of us, it isn't our first day at the rodeo. We talk to the same crews, same flights and work the same sectors a million hours per year. The experience level for dealing with these senarios is very high- maybe crews will do 3-4 departures per day, we work dozens. It is often we know that the rate is not going to work before the crew even realizes :)

[thealps]

I also work in central Europe, neigbouring Germany, and I can say we use rate of climb a lot. Actually I would be prepared to say that without rate of climb we would probably have to reduce the capacity of our ACC sectors by at least 30%, if not more (creating even more delays). I would estimate around 70% of all our traffic is either climbing or descending so assigning rates is essential to keep them all apart.

I’m aware of the complexity of an aircraft’s performance in climb, and the difficulty to predict for how long a certain rate of climb could be kept. Most controllers are certainly not aware of all the issues concerning the aircrafts’ performance, we do, however, have a lot of experience in handling traffic at all different FL:s and of all different kinds. We know what we can expect, maybe not exactly but just about. I definitely agree with the statement that we trust some crews (or airlines) more than others, that’s the way it is and what experience has shown us.
With the traffic we are facing each day rates of climb is absolutely essential in our work and very often separation is based on it. Sometimes I have the feeling crews are not aware of that. I don’t blame them but, in case of doubt, we’d so much rather have someone telling us they can’t make their assigned rate, if they’re not sure, than someone trying desperatly to comply and then failing. Saying ”negative” is never an issue with us, then we at least know and can work out a different plan. Of course, even if we do base separation on assigned rates, we always have to have a plan B but that usually includes turning two aircraft, often creating even more problems in an airspace where there is traffic all over.
If I ask a crew if they can do a certain rate up to a specific FL and they say yes, then I trust them. I base my separation on that answer (still with a back-up plan of course, should they not make it). We can enter specific rates in our system and our conflict manager tool tells us if it’s sufficient. We are also introducing a vertical rate adherence monitoring, which gives you an alarm if the assigned rate is not kept. We always see the rate of climb/descend (on the radar tracks and in mode S) but if you’re very busy you might miss that someone is not keeping their assigned rate. Should be another good safety net once that is introduced.
We also work with mode S and can see selected altitude, vertical rate, IAS, GS, bank angle, calculated wind and mach nr. It’s often very helpful. Especially since we get an alarm if the selected altitude does not correspond to the one we click into our system.

So to summarize - the majority of controllers are not experts in aircraft speed management and might be naive at times when it comes to assigning rate of climb. At the same time we do know that any answer a crew gives us is an estimate and not a promise. We will, however, treat it as a promise until we’re told otherwise. That’s why it’s so important that we are informed as soon as there is any doubt that an assigned rate can be kept.
In general it works very well and most airlines and crews inform us in time, it’s just the rather few times it doesn’t happen that’s the problem.
We are all doing our best in these times, with an enormous traffic increase, and I enjoy the cooperation with the flight crews. Talk to you soon.