Say you're cruising at FL240 at a IAS of 290-310 kts. If you're asked by ATC to reduce to 250kts (hypothetically

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If aircraft have to reduce their speed below a speed that is 'normal' for descent it would indeed be better to let them descend a bit earlier so that they are below the altitude profile and then they can reduce the speed and is the less steeper descent more manageable. Of course the most efficient (excluding operational or time costs, but fuel wise) is to reduce the speed already just prior descent and have a continious descend to avoid a level segment at lower altitude. But of course in busy airspace or airports this is most of the time not feasible I assume
Yep that's the way we like it!Atco EBBR wrote: ↑18 Oct 2019, 12:52Thanks for the reply, I knew that a lower speed implied a lower rate of descent, but I didn't know that that was not compensated by the lower speed...
So basically, if I want to sequence using speed control instead of vectoring, I need to first descend with a good rate and then reduce the speed.
You could! It's the same principle with your aircraftjan_olieslagers wrote: ↑18 Oct 2019, 16:52This makes for most interesting reading, thanks for sharing!
Myself limited to FL120 or so for lack of pressurisation/oxygen bottles, and to 100 kts Vne for lack of budgetcannot really contribute to the facts, so sorry...
Hmmm... always dreamed to do that on short final too... but nope, not allowedjan_olieslagers wrote: ↑18 Oct 2019, 17:53thank you!
If I wish to descend rapidly - which is standard practice under certain conditions - a sideslip is the standard answer. Which will indeed increase drag dramatically, while at the same time reducing wing efficiency, thus reducing lift. And I absolutely love side-slipping! But I can imagine it is one of those things one doesn't do to the unsuspecting innocent passengers of an airliner...
Yes indeed, top of descent is in most cases much earlier than Brussels Acc. It will require very performant, interconnected ATC systems to do a pre-sequencing using speed control starting at cruise level. Something to aim forOf course the most efficient (excluding operational or time costs, but fuel wise) is to reduce the speed already just prior descent and have a continious descend to avoid a level segment at lower altitude. But of course in busy airspace or airports this is most of the time not feasible I assume![]()
If you encounter such a situation, you can be sure that the controller has screwed him/herselfThe most difficult is when they keep you high during vectoring, and then ask you to reduce to 210-220kts and descend at the same time. This is very difficult to manage as the speed brakes have very few effect with such a low speed. In that case you have to give priority to speed or to altitude.
No idea who you're talking aboutThat's until cost index n°6 airline arrives in the way with their 245kts as from ToD though...
Most airlines (unless the pilots are paid by the hour) use a descent speed of about 280kts.
Unless you're in the Gimli glider, that isHmmm... always dreamed to do that on short final too... but nope, not allowedjan_olieslagers wrote: ↑Yesterday, 17:53
:If I wish to descend rapidly - which is standard practice under certain conditions - a sideslip is the standard answer. Which will indeed increase drag dramatically, while at the same time reducing wing efficiency, thus reducing lift. And I absolutely love side-slipping! But I can imagine it is one of those things one doesn't do to the unsuspecting innocent passengers of an airliner...
Funny thing is, I recently had a talk with a colleague from approach who had a plane (E190 iirc) at FL80 15nm final. I was surprised to hear that in order to catch the glide they ask to reduce instead of increase. That's not a thing that would happen in an ACC environmentHowever, if you're still too high and/or too fast close to the airport, increasing speed doesn't make sense anymore (of course). It's time to slow down and increase drag with the landing gear & flaps
Probably for the same reason, sequencing arrivals is on of the most difficult things to learn for trainee controllers. You really need to grow experience on what speeds and levels are 'right' and what is too fast/slow, too high/low...Descent planning (or energy management) is one of the most difficult thing to learn for ab-initio F/O's. It can be tricky as a descent is never the same twice; it depends on traffic, wind, speed, distance to be flown etc... On top of that, it also needs to be performed in an efficient way; that's where you can save fuel.
Very interesting read guys, let's continue this way.737MAX wrote: ↑19 Oct 2019, 09:23Hmmm... always dreamed to do that on short final too... but nope, not allowedjan_olieslagers wrote: ↑18 Oct 2019, 17:53thank you!
If I wish to descend rapidly - which is standard practice under certain conditions - a sideslip is the standard answer. Which will indeed increase drag dramatically, while at the same time reducing wing efficiency, thus reducing lift. And I absolutely love side-slipping! But I can imagine it is one of those things one doesn't do to the unsuspecting innocent passengers of an airliner...
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However, if you're still too high and/or too fast close to the airport, increasing speed doesn't make sense anymore (of course). It's time to slow down and increase drag with the landing gear & flaps.
To give an idea; the rate of descent at minimum clean speed (approx 210kts on a 737NG) is around 1000ft; increasing to easily 3000ft+/min with 300kts.
Descent planning (or energy management) is one of the most difficult thing to learn for ab-initio F/O's. It can be tricky as a descent is never the same twice; it depends on traffic, wind, speed, distance to be flown etc... On top of that, it also needs to be performed in an efficient way; that's where you can save fuel.
Yep... isn't that called the "single European sky" project?
In Belgium most of the time indeed. Free speed for most belgian airlines mean 280kts or more, but for some (Cost Index 6 is the airline where you have to pay for your hand luggage, you know...) the standard descent speed is +/- 245kts and has to be strictly respected by the company unless they become too high on descent profile and increase speed to catch up. Cost index, for those who don't know, is a relation between the aircraft cost per hour and the fuel cost, basically. The lower the index is, the lower the speed will be and vice versa. This index is therefore different for every airline.No idea who you're talking aboutBut rest assured, these 245kts airliners very often get slapped with a speed of 300kts on first contact
. The pilots are usually very happy with that, they often ask spontanuously if there is any speed control... If I can, my reply is 'negative, free speed', which would make all other pilots happy...
On the 737, the maximum gear extension speed is 270kts (you can increase further to maximum speed once the gear is extended). However an extension at 270kts is very noisy and thus not comfortable for our pax. That's an option we use when there is no other choice. But indeed, when you're so close to the glide you have to reduce speed and increase drag with flaps & gear, otherwise you'll never make it.
Funny thing is, I recently had a talk with a colleague from approach who had a plane (E190 iirc) at FL80 15nm final. I was surprised to hear that in order to catch the glide they ask to reduce instead of increase. That's not a thing that would happen in an ACC environmentWhat would be a typical maximum speed to extent the gear?
I can imagine! Add to that annoying pilots who want to fly different speeds all the time -)
Probably for the same reason, sequencing arrivals is on of the most difficult things to learn for trainee controllers. You really need to grow experience on what speeds and levels are 'right' and what is too fast/slow, too high/low...
For a 737NG, you have to multiply the distance to be flown by 3 to get the altitude at which you should be to be on the optimum descent profile (example; if you have 60NM to fly, you should be at approx FL180 or 18000ft).HQ_BRU_Lover wrote: ↑19 Oct 2019, 15:54
@737MAX: can you give an example of descent planning, f.e. ARVOL STAR 25L in EBBR? Or giving an example is impossible as winds, traffic, weight are not known?
It's strange that you say FL240 at the boundary is too low. Whenever possible, I use 'when ready descent...' and almost never I see an aircraft leveling of at FL240 to start the descent later. Coming from KOK yes, then quite often descent starts 10 nm or more past KOK...Arriving via ARVOL 25L in Brussels means FL240 at the boundary (which is too low) and you will have to maintain FL80 until you are abeam with RWY25R north of Brussels as departing traffic is cleared to FL60/FL70 below you. You become then too high if you are all by yourself, and possibly too low if ATC requires extra miles due to traffic. When possible for ATC, you'll be given the track miles they expect you to fly so you can adapt accordingly (ironically, that is usually not given when there is too much traffic and that's when you would need it the most...).
The trick is not to allow pilots to choose their speedI can imagine! Add to that annoying pilots who want to fly different speeds all the time -)Probably for the same reason, sequencing arrivals is on of the most difficult things to learn for trainee controllers. You really need to grow experience on what speeds and levels are 'right' and what is too fast/slow, too high/low...
I have to say that in Belgium, ATCO's are quite well trained for efficient vectoring.
The trick is not to allow pilots to choose their speed
I cannot speak about modern planes, but from a programmer's point of view it would be a lot easier. I have over and again insisted that, in the 21st century, magnetic information should be used only in extreme cases - after all, who uses a compass, today? Using only "true" headings would, for one example, get us rid of the changing of runway ID's every so many years. And true headings are not that difficult to calculate with trigoniometric difference calculations between (gps-derived) coordinates. Adjusting for magvar* adds a lot of complexity, since magvar changes both with location and with time. There are solutions to that, but the problem shouldn't exist.Could a modern aircraft fly a track, just as easily?
How many track miles from the boundary to the ILS25L for a usual approach into BRU?Atco EBBR wrote: ↑27 Nov 2019, 13:32
It's strange that you say FL240 at the boundary is too low. Whenever possible, I use 'when ready descent...' and almost never I see an aircraft leveling of at FL240 to start the descent later. Coming from KOK yes, then quite often descent starts 10 nm or more past KOK...
The problem with the track miles is that you have to calculate this case by case, the system doesn't know this. Say it takes around 5 seconds to calculate and you'll know why you can get that information only when it's calm... And we do realize it's very useful information when it's busy. A good arrival managing system should be able to handle that, hopefully that'll come with next ATC system (2022-2025?)
I like that!The trick is not to allow pilots to choose their speed
And thanks for the compliment![]()
On the 737 you can only select a heading on the autopilot, you would need to adapt the heading by yourself to continue on the requested track. But for modern planes (Another question for the pilots here: when we vector, you are given a heading. Could a modern aircraft fly a track, just as easily? That would be easier and more precise...