TOP of descent, and descent monitoring. (A320)

[WhySoTough]

Bare with the newbie please guys, I've got another question.
Is the right way to calculate TOD "altitude to lose multiplied by 3 and add 10" miles for deceleration?
If I find that multiplying my current distance times 3 plus 10 to be easier, I could also be doing that I assume?

Every how many miles do you cross check this?

Yesterday on my very first flight of line training, the captain decided to use open descent instead of managed(can anyone think why)? Yes we were in Nav.
He asked me to keep telling him if he was high or low and to use the alt to use times 3 technique. Personally it confuses me, but it was the first time for me doing this.

Any input, advice, examples, tips are welcome. :ok:

Thanks in advance!

[felixthecat]

Maybe he was doing it so that you had to monitor the descent and correct it. In VNAV (I'm Boeing) equating to the managed mode it calculates it for you and keeps you on the path (generally…with some exceptions)

You often don't know exactly how far you have to run so the 3x height plus 10 is a great way to monitor your descent, and work it into your expected distance to run….remember that the arrival you have in the FMC is generally giving you way more track miles that you will actually do due to vectors etc etc.

Remember to take into account the head/tail wind and correct for it also…

You should monitor the descent all the way down, I do a cross check about every 5-10000ft and more often as I get closer to the airfield and the ground. Don't just rely on the automatics…rubbish in rubbish out…..:ok:

[sevenstrokeroll]

back before FADEC and FMS we managed our descents quite well with the following idea. Mind you we didn't even have a DME ground speed readout...just DME mileage.

Let's say you are at FL310 with a descent clearance to FL200

11(,000) feet to lose, so 11 (thousand) times 3= 33 miles (nautical) to lose the altitude...but no smooth level out or option to decelerate if there is a clearance or requirement to do so. So, ADD 10 nautical miles as a "FUDGE" factor...this in case you get an increase in groundspeed due to unknown changes in wind.

so, 33 plus 10 = 43 miles before any required crossing fix, start your descent.

AH, but what rate of descent?

multiply your groundspeed ( in knots) by 5....let's say you are doing 500 knots
in this case 500 knots times 5 =2500 (this in feet per minute). So, start your descent at 2500 fpm and you should be fine.

Its not alot of heavy lifting.

You can use your watch/clock to make a caluclation of groundspeed based on changes in DME readout.

During the course of the descent, recalculate and see if you are still going to make the crossing restriction.

AND, remember, it is very UNLIKELY that you will be doing more than 700 knots groundspeed...so if you don't even know your groundspeed, you can use 700 times 5 =3500fpm in case. you will be early in your descent, but that's only fuel!

I always get a kick out of how we now have to make the machine happen instead of other way 'round. Just before takeoff, I watched one super duper FMS equipped wonder jet get a re route from ATC. It took the crew 10 minutes to load the re route. In prehistoric times we would have taken off and headed to first fix (VOR) and just kept up with it, like sight reading a piece of music.

And one more thing...I just wonder if sucking birds into a FADEC equipped engine compared to the same engine NON FADED would have the same result... a FADEC commanded shutdown or reduced thrust. Still think if Sully was flying a DC9 with JT8d's and sucked birds he would have made his destination on time.

[BOAC]

If I find that multiplying my current distance times 3 plus 10 to be easier, I could also be doing that I assume? - ?? What are you trying to work out there?

Descent will take just over 20 minutes to 3000', give or take, which is 1/3 of an hour, thus allow 1/3 of the wind ie 20 kts allow 6-7 miles. In ssr's and my day it was 3 miles per 10 kts. Same cat....

Ball park 'check points':

Around 20,000ft at 70 track miles to run, and 10,000 at 30 (at 250kts)

the captain decided to use open descent instead of managed(can anyone think why)? - yes! Stick with what your TC was getting you to do - watching an FMC managed descent will teach you very little!

[Lord Spandex Masher]

Select FPA, twiddle to 3.0 degrees and Bob's your mother's brother.

Oops. There I go sounding like somebody who like a colour close to pink! :yuk:

Is the Airbus even that advanced?

[WhySoTough]

Thank you all very the quick, informative responses.

Felix,

Thanks for the reply.
Makes sense. If you had a headwind, would u multiply alt x 3 and add 5 maybe?

Sevenstrokerroll,

Thanks. I understand better now.
Though now I have more questions.
Firstly if the ATC gave me an initial clearance to descent from FL 310 to FL 200, wouldn't it be better to still do the 31 x 3 plus 10, since I know I'm most probably going to be given further descent clearance?
If ATC were to tell me to be at Fl200 by a certain point, i would definitely start my descent and use the 43 miles in this case.
Right idea?

Also,
If I was using the V/S, I don't think it would be a good idea to use speed breaks. I could be wrong here, please do tell.
Basically don't use speed breaks, and just increase V/S if I am above my profile?


BOAC,

What I meant was, instead of altitude to lose x 3 plus 10.
Example if I'm at 20,000 feet. I should be approx 70 miles for a nice constant 3 degree descent angle.
Instead of that I'd see my track miles, for this example I will use 70 miles.
So 70 x 3 plus 10. I should be at 22,000 feet.

The captain said this was another way to calculate. Though it gives me slightly different numbers. :ugh:

[flapsupdown]

WhySoTough,

Just wanted to share some info with you - hopefully will help answer some of your questions.

Using speedbrake in V/S: there is nothing wrong with doing so as long as you are aware of what the autopilot mode is trying to achieve. In V/S the autopilot is maintaining a selected rate of descent. As such, using speedbrakes will only reduce your airspeed, it will NOT change the rate of descent.

When you are talking about your descent - whether it is ALT x 3 or Dist x 3, you have to remember that all this means nothing without taking into account your speed. If you are below the "profile" (within reason) but your speed is high, or you are above the "profile" (within reason) but your speed is low, its not really worth getting back on profile immediately. I guess what I am trying to say is that you need to be thinking about this with your airspeed in mind.

[Lord Spandex Masher]

In V/S the autopilot is maintaining a selected rate of descent. As such, using speedbrakes will only reduce your airspeed, it will NOT change the rate of descent.

But, it will change your angle of descent.

[sevenstrokeroll]

why so tough:

indeed if ATC is predictable in a total way, make the calculation down to 10,000
feet above touchdown/airport...things change at 10 to the 250 below ten rules in many places.

now...I would LOVE to tell you that you will get an uninterrupted, perfect descent to touchdown. I"ve had that ONCE in 30 years of flying. And be sure to rev up your engines at least once to make sure they are spooled up....or ready for action, or whatever you guys say now a days...don't get caught like that BA 777 guy in London. Not that I am blaming him per se.

It is always cool to NOT need speed BRAKES (not breaks) but if you need them, use them.

There are lots of reasons to stay high...but there are good ones to get down early.


I know here in the good old USA, if you get below FL230, you get into the lower sectors and can sometimes get DIRECT! Indeed, one day in my DC9, our pressurization was out and we flew 5 legs at 10,000'....including Montreal To Baltimore. Well, we thought we would use more fuel...but because we were the ONLY plane at 10,000 feet that day, we got DIRECT everywhere...on time, under fuel burn.

Those guys that blindly stay high are not always right (transoceanic legs aside)

good luck, happy flying....and remember its YOUR LICENSE not the computer's!

[Microburst2002]

the captain decided to use open descent instead of managed(can anyone think why)?

there is many a reason

WST

Sorry for asking, but is the 320 your first airliner?
Disregard any advice from a training captain that tells you to keep always DES. Many do it. Disregard it.

The third dimension is the whole point of flying, and being a pilot is all about the third dimension. You must be capable of knowing if you are high or low at any time without the need of a magenta donut.

In the first place, the computer will only give you good profile information when the airplane lateral fpln is going to be made good. And if all data is inserted correctly, and if planned speeds are going to be maintained as planned.

Many many many pilots do this:
they fly in OP DES when instructed to fly a much higher speed, then when recapturing the profile, the donut, they manage descent again, but keeping the high speed. In fact they are high, because they have extra energy due to the extra speed. They are blindly following the computer.

You must know your required distance to land as a result of your altitude and speed. The rule of thumb FLx3 +10 is quite good, but can be refined. Some airplanes sink like stones, others glide like sailplanes.

During descent, altitude is what you know. Distance to go is not always known, so work parting from your altitude. Then decide which distance you think you will fly to touchdown, then find if you are high or low. Only if the FPLN is updated so that you have in it what you will actually fly you can trust the donut. So many times it is not the case! You have to look at your ND and visually see the likely distance to go. Many times is radically different. If you are a donut follower you will never master the third dimension. If you don't you can barely call yourself a pilot.

Take every oportunity to fly in OP DES until you master the way your airplane descends, then when you use DES, just monitor its consistency.

[felixthecat]

If you had a headwind, would u multiply alt x 3 and add 5 maybe?

Its not quite as easy as that. You may +/- 5 or more it depends on the winds. Thats the important thing about monitoring your descent so you can adjust it as you go.

If its a headwind you will need to take away miles and a tailwind add them not the other way around as you quote. A headwind will increase your air distance and a tailwind decrease it.

Sit down and think, learn some gates for your aircraft type i.e. at 5000 at FL100 at FL200 at FL 300

Learn the aircraft and work out your own profiles then you will be able to use managed profiles and know if they are giving you the right information or not. Be conservative, especially as a new guy….don't get high and fast ( easily done when chasing a profile ) low and slow is just costing you a little fuel but buys you thinking time as a new guy. The profiles will get better and better as you get more used to it. After a while you will just "know" if your high….

Happy Flighting :)

[Microburst2002]

In my models (CFM, old with extra drag) FLx3 + 10 is the basic for a GW of 60 T, 300 kt, 250 at 10,000 ft. Below 10,000, use FLx3 + 6. As you build hours, it should be sufficient with that, but you can refine it a lot, when you get used to do quick mental calculations.

For very heavy, I increase the distance a 10%. For very light I increase a 10%, for super light, a 20%.

For wind, add or substract a 5% per each average 20 kt component. You can calculate that with the vertical wind profile in your CFP, and then monitor during descent.

For a higher speed, such as 330 knots, reduce a 10%. For slow speed, such as 270, increase 10%.

What I do is add up all corrections and apply to the basic FLx3, then add the 10 NM for deceleration, 8 if light. Below 10,000 add only 6.

Seems complicated but I do it real quick thanks to practice. I am absolutely not worried ever about 3rd dimension when I fly. It gives me a lot of peace of mind when I fly for that reason. The FMGC never gets me in trouble.

During the descent, monitor your gradient. That will tell you if your calculations were accurate enough. Do the following:

fpm / GS in NM = fpnm

GS in NM is easy. Look at your GS, then remember this table:

240 kt is 4 NM/min
300 kt is 5 NM/min
360 kt is 6
420 kt is 7
480 kt is 8
540 kt is 9

If you are making 2,100 fpm at a 420 kt GS, your gradient is 300 fpnm. 330 fpm is FLx3, so your gradient is now a 10% shallower than that. You should be doing 2,300 or so to be on the FLx3. If your gradient was 400 fpnm then your angle is a 20% steeper. Keep monitoring since gradient varies constantly but tends to oscillate about an average value. That will tell you if you will tend to get high or low. GS and fpm will change constantly. Soon you will know if the actual gradient was too much or too little. The different of that gradient with the gradient in still air (using TAS instead of GS) will give you a hint on what is the effect of the wind.

If you see you are high when still at high level, it is very easy to recover. The change in energy by increasing speed for a while means you will dive and loose a lot of height due to the acceleration only. Shortly after being again on profile, reduce back to your target speed. During deceleration your rate reduces, yes, but the net effect is an energy loss, exactly what you need. This process is energy wasting, like using speedbrakes, but gives you less flight time in exchange.

If you are low, just select V/S -1000 ft until you are again on profile.

A perfectly calculated OP DES will make the airplane descend at constant speed, while the magenta donut will go up and down, but it will come to you, instead of you going to it.

At 10,000 ft and 250 kt you should have 38 miles to go.

As you get closer to the field, calculations are easier because the effect of GW or wind are less, in terms of feet. The basic FLx3 + 10 will nearly always be good enough below 5,000 ft.

With time you will learn by heart:

5,000 ft, 21 miles (5x3 + 6)
4,000 ft, 18
3,000 ft, 15
(if you are at 250 of course. add 1 mile per extra 10 kt which is conservative enough. only half if you are light and/or with a headwind)

When you have green dot, FLx3 plus 3 is good enough.

When S, FLx3 is good enough.

These ones are particularly helpful during approach, specially when being vectored.

During approach, if your speed is significantly different than that of the magenta profile, this profile will be in significant error. Typically if you are flying at 200 kt but the profile is for 250, you might think you are high with the donut below when you are actually low...

It may seem too much maths, but is always the same, you will get used to it with practice and it will give you peace of mind in the 3rd dimension, which means a lot of spare mind for so many other tasks.

As a note, for TOD calculation from high cruising flight level, this is accurate enough if at TOD you don't pull OP DES right away but instead select V/S -fpm for 330 fpnm (still air) and then let the airplane accelerate to target IAS while maintaining target mach. Otherwise the acceleration will be a dive, very steep if the airplane is light and the target speed is high. This would give very high rates, reduce the time to descend to field altitude and increase the average cabin rate That is why the FMGC does a similar thing, the repressurization segment.

For instance, for a 464 TAS indicated (approx 480 kt, that is 8 NM/min), I will gradually select a V/S of 2,700 fpm (less if req to avoid MMO exceedance). IAS will increase gradually. MACH will command thrust to maintain mach number. As IAS increases for the constant mach, the target is ahead of actual speed and thrust is thus much higher than idle, but after a while you'll be reaching target IAS, SPEED will be in command of thrust, now, and it will reduce to idle, then you can pull OP DES.

If captains allow you to do that, of course...

[Ollie Onion]

Gidday,

I have found you are best just to keep it simple. I personally use 3 x altitude + 10 nm for calculating T.O.D. From there on in just a basic 3 x table to monitor the descent.

So from 35,000 I would plan on TOD being approx (3x35)+10 = 115nm to run. Once I start down you just keep a running total going in the background.

So:

So at 20,000 ft if you have less than 60nm to run then you need to increase your rate of descent.

At 10,000ft you should have no less than 30nm to run and aim to be at 250kts.

From there aim to be at G/S intercept at Flap 1 S speed.

[felixthecat]

I agree with Onion….KISS principle works best…Keep It Simple Stupid…...

[Microburst2002]

It may be simple, but 30 miles at 10,000 with 250 you are about 2,000 ft high. That is pretty much at that stage...

So are you at 20,000 ft with only 60 nm to go, but maybe not if you are light or there is a noticeable HW, or the airplane is very "draggy".

I keep it simple, but within reason.

Try to pull OP DES exactly ar the FMGS calculated TOD, at FL390, GW 49 T with an AUTO speed of .80/330 knots. You will get Veeeery low, even if the FMGS has into account GW, because of the lack of repressurization segment when in OP DES.

Or try to use FLx3 plus 10 in that day. Tou will see that your TOD is over 20 miles before FMGS' TOD.

Durin approach, it is actually simple: FLx3 + decc, decc being 6 at 250, 3 at green dot, nil at S or at 180.

[Natstrackalpha]

what a cool thread
Quote:
In V/S the autopilot is maintaining a selected rate of descent. As such, using speedbrakes will only reduce your airspeed, it will NOT change the rate of descent.
But, it will change your angle of descent. Magic, well I think so . .

My theory is for the Thick, like me, and, being thick I need building block solutions to move forward: based largely on the above (most excellent) posts.

3x alt = dist (no 10 added)
sw from Mach to spd and start down at that spd (intially, for a bit)
monitored by me/her or us selected spd all the way down -
based on 3 times table only (no 10)
280 generally, say, then 250 by 10,000
We put us `by 12 miles` spd 210
by 10 miles gives +/-3000`
spd 180 by 8 miles about 2400`
160 by 6 miles and into landing configiurations - 3 flaps down by here
at 4.5 miles will have gear down and be selecting FULL and managed spd or going around
Even if being vectored with no height, I find this a cool system needing only a quick looky see calc to determine track miles (and not dist to TD)- Big Notwithstanding MSA, ground to hit/buildings OCL etcetera.

ADDED LATER ON: By the way, the/my above profile, in Selected, is almost the same profile, (speeds too !) as if it were all done in Managed.
. . . and a - ive, what I don`t like about V/S is that it does not honour Alt constraints. . . as we all know . . . and, per se` I don`t like Open Descent much either, not that I have problems, it is just that, well, to be ahead of the aircraft is fundemental for this a/c, if you are in V/S . . .

[Microburst2002]

at 5,000 ft at 250 kt, FLx3 is 15 nm

You are high, very high, because now you are too close. You will have to take positive actions, maybe a not very stabilized approach if wind and weight are inconvenient.

FLx3 + 6 is 21, you are confortably on profile. mile more mile less, but 6 miles difference is too much.

[macdo]

Talk about over complicating things, the answer is yes! But most people just do Managed Descent at the down arrow!

[Microburst2002]

And many of them screw descents very frequently because of that...

[macdo]

I disagree, IMHO, so long as you have adequately programmed the FMGC for the anticipated approach, I find that the FMGS calculated down arrow is almost always correct. Some local knowledge for early ATC descents, short cuts, speed control will help as they can be programmed in, as will the having the capacity and spatial awareness to see how the FMGC might need modifying as you progress to destination, but this is all part of the job. A good example would be Larnaca in Cyprus rwy 22, where you can easily let the FMGC fly from top of drop on the STAR to short final on the ILS with no intervention. In twelve years of flying the bus for a major carrier I have very rarely seen anyone not use the down arrow and it is certainly what our excellent trainers would expect unless there was a good case for 'going non-standard'. The small bus is very flexible and usually produces a reasonable stab at the down arrow, even if you forget to put the winds in! I'm a bit puzzled by your comment that you see "plenty of people screwing up their descents", if that is happening, there must be a problem with the way these people are being taught to do them.

[PT6A]

I agree with the above, just make sure the box has something realistic in it.

Then that is most economical way to fly, and is the SOP at my place.. To keep it updated and stay managed.

[WhySoTough]

Thank you all VERY much for the responses.
Lots of informative and useful posts.
Someone asked if its my first airline job, and to answer your question, yes it is.

At the moment being new to all of this. Not just the aircraft but also real world flying, would it work out fine for me if I just used the simple method of, altitude to lose X 3 plus 10. If my track miles are more than what I get from this simple formula, obviously I'm below profile, and if less track miles than calculated, I'm high.
In addition to that, I can Increase speed Or use speed breaks to descend lower, decrease speed to reduce V/S.

Would it be okay to use this simple method for now, not to complicate the whole scenario even more, as basically EVERYTHING is new to me at this point.

Also, yet another stupid question.
What is the difference if I increased V/S, or just ncreased speed.
I believe ncreasing V/S will increase speed as needed to give the V/S set.

[BOAC]

Also, yet another stupid question.
What is the difference if I increased V/S, or just increased speed.
I believe increasing V/S will increase speed as needed to give the V/S set. - it is fairly basic physics! I suggest the easiest way, if you cannot/do not want to try it on a line trip or work it out at home, is to run a flight sim programme and see what happens.

The only other advice I would give you is to remember the effect of wind (see my post #4) particularly in calculating ToD - and it will change on the way down - and to always add on a 'bit for mum' in your early days (the first 5 or so sectors) by descending, say, 5 miles early, so you don't get 'high'. I'm sure a decent TC will not have an apoplexy:)

[macdo]

Standard Airbus technique if HIGH on the profile as indicated by your magenta deviation 'donut' (yes i know its not a donut anymore on the latest revision of the fmgc, before anyone points it out!) is OPEN DESCENT and increase SELECTED SPEED, if you remain fully MANAGED, deploy 1/2 speedbreak in order to meet the 'rejoined profile' down arrow, either works fine, but the OPEN DES method is more decisive. If low then VS and SELECTED SPEED, (managed speed can be used, but some trainers like to see that you are accepting control over the FMGC by Selecting your speed as well as your RoD.) When back on the profile, go back to fully managed. The only time you really need to calculate the Distance vs Altitude is when on vectors and you have cleared the FMGC to only show the Approach from the Final (or Centr) fix to the GA point. The donut is still there to help you, but backing it up with some mental arithmetic is good.
The Airbus concept is smart aircraft for dumb pilots and largely you can use this philosophy safely to make your life easy, which suits me fine. BUT, what Airbus don't say on the tin is that buried away inside your clever aircraft are lots of traps for the unwary in the form of computer glitches and oddities of logic. Your mission is to be ahead of the aircraft and have a really good understanding to the FMGC and the automatics, cause if you don't some dark and stormy night your friendly Airbus will bite you on the backside.

[Microburst2002]

There are several reasons for a pilot of a 320 to be proficient in accurately calculating a TOD and monitoring a descent without the FMGS.

The first of them is the need to check the reasonableness of the FMGS predictions and indications.

It is very difficult to be proficient at that if you don't practice.

It also gives you independence, since sometimes it is be too complicated to set the lateral navigation with the MCDU. It is much better to carry out the descent (or typically a part of it) with selected modes.

Even for full descents. In many airports you are never going to fly the FMGC depicted FPLN. You may bet to one of several possibilities, but there is no use in changing all the FPLN just based one of those possibilities. It is better to base your descent in that possibility without major changes in the MCDU. You are betting on a given track and distance to go, which may be radically different to that in the MCDU. You have to make calculations of your own.

An example: flying to Dubai Intl 30L coming from the gulf, from northwest, the arrival takes you to the runway via a right downwind, a base and then final. There are many altitud restrictions so that you are quite low all throughout the arrival. Then, in final, many get high because they follow the donut. What a nonsense. Because if you are number one or two you are not going to fly All those miles. So what you do is: at your mentally calculated TOD for those miles you expect to fly, from say the 10,000 ft you are maintaining, you pull OP DES. When they give you the shortcut you are on profile. If you are on the donut, you are high so they don't give it to you altogether. This may save 2 minutes ore more. Of course, if there is a lot of traffic, you are number 6, just follow the donut, or even fly somewhat above it...

Optimizing takes some thinking. Efforts to avoid thinking are no good.

[macdo]

Glad you agree with me...:D

[Oldaircrew]

WsT

Firstly, your instructor is trying to teach you how to manage the descent on your own. It is very seldom that you will fly an entirely managed descent in todays ATC environment. Vectors are a very important tool in the ATCs armoury and then you will need to know how the aircraft is performing wrt the descent. Take heed of his lessons, he is doing you a favour.

Secondly, despite some peoples reverence for the FMGS, it is not the most efficient way to manage a descent, especially in an A320 with IAE engines. It is very conservative(for good reason) and you will often find yourself low and having to intervene with V/S. A point to remember is that while V/S can be helpful, you lose a lot of protections and therefore it is not the best way to descend for extended periods of time.

As to being high, remember your Aero-d lectures/lessons. The co-eff of drag, like that of lift is depend on the speed of the a/c. Therefore, the higher the speed, the more the drag and the quicker you will descend resulting in a requirement for less distance for the high speed descent.

Finally, and for me personally the most important, is that it is more fun to manage your own descent and therefore the most fulfilling. Not much(from a work point of view) beats the feeling of idle from TOD to stable at 1000'(which I have to admit, doesn't happen all that often but I do try).

[500 above]

A good example would be Larnaca in Cyprus rwy 22, where you can easily let the FMGC fly from top of drop on the STAR to short final on the ILS with no intervention

I must be based from a different LCA then :)

I assume you mostly use the Daros 2A, then that would make sense. Chaos corner, indeed.

Try any other arrival into LCA and the boxes profile goes out of the window.

[macdo]

As you say, Daros2a works a treat, you just have to watch out for the altitude restriction at SOLAB as sometimes it is not coded and must be entered manually. This was my best example. The only reason this sticks in my mind is because years ago I had a bet with a skipper who said he could get the a/c to fly the whole thing from Tombo fully managed and I was a' doubting thomas! I lost the bet. At the time, as a new boy, i was keen to intervene at every point, but I now know that Managed flying on the 'bus is the most efficient way to operate it. I absolutely agree that you have got to be able to do all the mental gymnastics, but that is not the Airbus philosophy. For the new guy who started this thread, he should have already proved that he can do the mental arithmetic in a Seneca or something, and again IMHO, if I were a trainer I would be much more impressed with a deep understanding of the aircraft automation, than any ability to operate the a/c without it.

[Microburst2002]

There is a generation conflict here.

For the "veterans", automation looks like a very complex thing that achieves magically things that otherwise take a lot of mental work. So they do every effort to understand automation and the interface. They have flown manual or with old automation systems more than enough.

For the "freshmen", automation is a very simple thing (later they will learn it is not so simple, but it is just another computer in their life) and they won't even know what task the automation is relieving the pilot from if they never perform it on their own. They didn't have the opportunity.

In the Senecas, the mental gymnastics are different. I think that we must master both sides of the coin: brain and computer. Playing too much can lead to inefficiency or even trouble. Relying on automation too much can lead to that, too.

A classical example: you are cruising at FL 340 and ATC gives you an early constraint at say, FL 290 well away or the airport. If you just put the constraint and at the TOD manage the descent, then the airplane will do a nasty idle descent at 3,000 fpm and then capture 290, with the associated thrust increase. Instead, a simple math calculation and the use of V/S achieves a far better way of doing the job. Some make it even worse, they manage the descent well before the TOD, so they get 1,000 fpm. That's fine, but then the flight path captures the profile at maybe 1,500 ft above FL 290 and the airplane all of a sudden goes idle, pitches down, reaches 3,000 fpm, ALT *, pitch up again, N1 increasing rapidly again... So untidy!

I apply the automation rule (using the level of automation required for the task and conditions). For too many this rule is: "use highest automation level no matter what, except if you loose the automation" which makes no sense.

Airbus automation is very good and I like it very much. I trust it because I know it intimately and I know that if one day I need the computer to manage for me while I have to deal with some kind of emergency or situation I can rely on it.

[Natstrackalpha]

Sorry, if thread spread, am avidly reading all your posts to check if this has been answered -

actually, I have a Question.

don`t care if openeing myself up to criticism but:

I know I should know this, but suddenly have forgotten it - notwithstanding Alzheimers, or even spelling . . If at TOD I shall avoid all FMA and PFD checks for this scenario - (God this is so simple)

you are just before TOD say, and everything not mentioned here has been done . .
You set up a lower FL say FL170 and push and down you go,

If, if you select speed 280 say, then the descent is still managed but the speed is not.
A/P is still engaged.
A/Th is still in, (at work will get back to you )- anyway, will not the a/c manage the descent, except that your in Selected Spd and the descent will be managed as the aircraft tries to maintain the profile using pwr + att .

[Microburst2002]

Managed descent with selected speed, another untidy thing except if you are high on profile at a high speed. When on profile with a selected speed similar to ECON speed, SPEED and THR IDLE modes will alternate annoyingly.

If you select a low speed, you will get high. If you select a high speed, SPEED mode will keep the high speed an pitch will keep the profile, but... If speed is much higher, airplane energy is much higher too, and if you don't pull for an OP DES early enough, in the end you will have to use speedbrakes! That's another classic, by the way. I have seen it happen many times, as follows:

ATC clears us to a mid flight level, such as FL240, well away from arrival airport. Then pilot selects FL240 as the cruising FL, so you have a TOD in the MCDU. Pooblem is that ECON speeds will change and ECON descent speed may be quite slow, like 265 or something. So when reaching the TOD, the pilot pushes for DES and when realising speed is too slow he selects, say 320 knots (he wants to arrive early for supper).

Pitch will maintain the magenta profile, which is calculated for a 265 knots idle descent. SPEED mode increases thrust very noticeably to maintain that shallow path at 320 knots. Pilot requests "high speed below ten". Everything seems alright. Then there is a moment where the pilot, being on profile at, say, 20 miles, starts deceleration and then something smells rotten and the pilot deploys speedbrakes. Finally he manages to do the ILS only it took early configuration and speedbrakes all the way. Why? Because he had about 70 extra knots of energy. The profile was never good. He was never on profile. He has been using thrust all throughout the descent and at the end he had to use speedbrakes and early flaps, maybe even early gear down depending on the particular circumstances of the day.

These mistakes stem from two added factors:
incomplete knowledge of the airplane's managed automation plus lack of knowledge of the airplane performance and behaviour without the managed modes and without automation at all.

Both are unacceptable. Pilots must master both skills: managed and selected automation and manual flight.

[Natstrackalpha]

Cool, thanks for that. Really.

and . . point taken. (I thought I had . ., obviously not . .back to school, back to basics!)

Many thanks Microburst.

N.

================================
6 hours later: Ok, this is the situation . . .
The figures as above BUT - Start from ToD as per usual in managed, obviously go to spd from machno when appropriate. At the intermediate approach and subject to (because of) ATC then use Selected if necessary and depending largely on HWC or TWC or no wind, then . . use the firgures for 12 miles , 8, miles and 6 miles as above, "I did it myyyy way . " (joke) - Managed is good. Selected is more dans les mans (my French is c--p unlike my flying).
And . . on a slightly lighter note and with full consideration of those very responsible noise abatement people . . .would it not be better for eagle to be slightly high and sail it in, rather than bang on and drag it in . . hmmm? Also - and I mean this lovingly(within reason)) where is the premium on not being high and fast-ish? What is wrong with a bit of speebrake and early flaps / gear to slow - or were we already communicating . . .? . . hmmm?
I mean, on profile City is where I would like to be, but if have been reading some of the greats (like your good selves, most honourable gentle persons) and they are giving me speds like above, then it all must be happiness?

[Natstrackalpha]

Microburst
Ok, your mention of too high – is not really high in my book at 15 miles, its only 425 feet and at 15 miles 425 feet above profile does not seem all that much, or maybe I`m wrong. Having said that, 3xheight for range is good down to 10,000 say, and then you can back calc 3xrange for height

Your comments on Open descent are as you suggested most favourable, I am still happy with 33 miles at FL100 – notwithstanding alt constraint or spd constraint,
I would be looking for Green Dot or 210 at about 12 miles out or 8 miles if making an abeam approach, at 280 kts decelling to 250.

Eng Anti-Ice Off would give me some cool gates, thus:-
33 miles 10,000 280 max clean
20 miles 6000 250 clean
12…3800 210 or Green Dot Flap 1
8 ….2500 180 or S speed Flap 1
4.5...1500 160 or F speed Flap 2 or 3 plus Gear.

Times to reduce speed are 350-210 2 mins 10 secs Dist 10 NM
===================350-280 1 min 6 NM
===================280-210 1 min 10 secs 4 NM
Using speedbrakes to aid decell will reduce these times by approximately 40% deployed and retracted gently. ADDED LATER ON: also the slight pitch up tendency due to speedbrake may help to decell more effectively but brisk speedbrake retraction may cause a pitch down and potential altitude bust.

I also favour the constant power technique, but that is for another day.

[Microburst2002]

15 miles at 5,000 and 250 you are high, unless very light and/or strong headwind. That is how you would be with a FLx3 rule.

Anyway, I always prefer to calculate parting from my present altitude, speed and configuration. Distance to go is not clear every time and a don't need gates or specific sets of conditions.

I must say that most of the times, when FMGS FPLN is what I actually fly, my rule takes me with the donut. Only if conditions are special (weight and wind, basically) I deviate from that.

[RunSick]

Hi WST,
I´m in a similar situation as you and if I could, from my inexperience, recommend you something is to memorize (or write down and use in flight until memorized) the gates given above by NTA. It gives distances, altitudes AND speeds + config.
It helps A LOT. Later for sure you (and I hopefully) will get to the finer details also described in this very interesting thread, but this numbers will help you for now.

One other thing, yes, there is a direct relationship between V/S and speed. Modifying one will affect the other. Which one to use? I guess it is something up to each individual BUT I got an advice from a TC which for now I will keep and basically goes about using Selected Speed below 10,000 and not the V/S. Why? because that way you are sure you will not bust any speed limit.

Say you are doing 240 decending thorugh 6000, using V/S, then you get some vectors, now all of the sudden you are high... no problem, increase V/S and that´s it BUT then speed starts to creep up and suddenly you are doing say 255 AND already below 5000ft. NOT GOOD.

On the other hand, if in the same scenario you are using Selected Speed and then suddenly you are high, what would you do? Maybe think to increase speed, but then you will notice you are selecting (or about to select) something above the speed limit, and then you choose to use some speed brakes instead till on profile again.

I know it might sound basic for the more experienced but it does work, at least for me.

Then, just check the limits as: 250 below 10000, 230 near the Terminal area, and then, once you are getting closer to intercept, or turn base (if on vectors) select 2 or 3 knots below VFE next and keep it there. Why? Let´s say you thought you where going to get longer vectors, suddenly they turn you to intercept... if you are ALREADY in a safe speed (VFEnext -3): manage speed, request FLAP1 + GEAR DOWN and the speed will come back quickly and all will remain under control. But, if you have to wait for the speed to come back to VFEnext, and then start to configure to slow down and at the same time you want to get lower :bored: specially with tailwnd it might be a bit too late.

Other thing I learned (the hard way :\): sometimes it´s better to accept to be high for a brief period of time in order to be able to regain the profile. This applies to being left high by ATC close to the airfield. You might want to regain as usual with increasing speed, well, chances are you might not make it in the given distance, this increasing speed technique works better when FAR from the airfield. And anyway if you manage to do it (by increasing speed close to the airfield), as it has been pointed before, you will still have a lot of extra energy to get rid of in the form of speed. To prevent this situation it might be better to accept from the beginning that you will be high, SLOW DOWN (which will make you be even higher) and the put FLAP 1 GEAR and FLAP 2. If you manage to do this the airplane will sink very nice without any speed problems.

just my 2 cents (anyone please feel free to add correct any point)

[RunSick]

This also helps:

2000fpm -- 290kts
1500fpm -- 250kts
1000fpm -- 220kts

Yes, there are more variables into it, but as a gross reference it does help.

[Mikehotel152]

It would all work so well if it weren't for the uncertainties of ATC....

[Microburst2002]

Then we would be sleeping durong descent!

I like the uncertainties. That makes the descent more fun. Within reason, of course. I hate when they change runway or pricedure or sequence every two minutes, like in some airports I know...

[dream747]

If I am descending on profile in Des mode and in managed speed; and now I select a speed lower than the managed speed (while keeping in Des mode), would the aircraft actually disregard the selected speed and continue to be on profile or would it end up high because it'll reduce the pitch to slow down?

New on the Airbus as well and never actually got to try this.

[Microburst2002]

The airplane gets high, while maintaining selected speed, but honestly I'm not sure. It is not tidy to descend that way. I pull for OPEN DES with the speed selected, in those cases, and use speedbrake if necessary.

[macdo]

If you have SELECTED Speed and Managed DES the a/c will maintain the trajectory of the MANAGED DES profile in the FMGC. It will also attempt to satisfy your Selected Speed demand as best it can. If you are asking it to slow down, it will bring the engines to idle (if not already there) and attempt to give you any pitch up it can to reduce the speed back to the Selected Target. The only pitch up opportunity that will develop is when the FMGC finds itself slightly under its computed profile, possibly because the predicted winds are different to reality. It does work, but not very well. You can intervene and deploy 1/2 speedbrake until close to the Selected Speed target.
If you select a higer speed target, the FMGC will add thrust (SPEED will show in the FMA) to accelerate to the target.
As Microbusrt2002 says, this is untidy usage of the automatics and can easily lead to a 'whats it doing now?'. As a general rule don't mix SELECTED and MANAGED, although like all rules, there are times when it doesn't apply.

[dream747]

So am I right to conclude that profile still has priority over speed when a lower speed is selected while in Des mode? In the sense that it will pitch up to try its best to maintain the selected slower speed at idle but not at the expense of deviating from the descent profile?

I went through the books and I can't find anywhere where it states how the aircraft will deal with selected speed (lower than the managed target speed) while in Des mode on profile. It only explains the situation when you select a higher speed.

Thanks for the clarification guys.

[Ollie Onion]

Dream,

don't know if it is written anywhere but from my experience the speed is secondary to the profile. It will do the best it can to pitch up to reduce speed but as soon as it deviates from the profile in pitches down and lets the speed increase again until it is back or under profile.

[macdo]

DREAM
I think the following ref. from our FCOM explains it:

DSC – AIRCRAFT SYSTEMS
DSC-22_30 – AUTO FLIGHT - FLIGHT GUIDANCE
DSC-22_30-10 – General

The AP and FD pitch modes can control a target SPD/MACH or a vertical trajectory, and the A/THR
mode can control a fixed thrust or a target SPD/MACH. However, the AP/FD and the A/THR cannot
both control a target SPD/MACH and trajectory simultaneously.
Therefore the AP/FD pitch modes and A/THR mode are coordinated as follows:
- If an AP/FD pitch mode controls a vertical trajectory, the A/THR mode controls the target SPD/MACH.
- If an AP/FD pitch mode controls a target SPD or MACH, the A/THR mode controls the thrust.
- If no AP/FD pitch mode is engaged, the A/THR mode reverts to controlling the SPD/MACH mode.
In other words, the selection of an AP/FD pitch mode determines which mode the A/THR controls

There is a table afterwards but I can't copy and past it in.
In any case, you are quite correct.

[Microburst2002]

You know... I'm not sure who is primary. If pitch follows the profile, this should be maintained at the expense of higher speed, but speed should be primary to profile, in my opinion.

Question is what mode will ATHR have active in such scenario, very slow selected speed and steep profile with DES? THR IDLE or SPEED (with teh engines in idle)?

If is THR IDLE, then speed is primary. That's what happens in my opinion, but as I say, I always use OP DES in such cases. If it was, SPEED, however, then profile would be primary.

[Natstrackalpha]

Constant power.

See what your Green dot is at level flight. Note the N1. T`will be about 10% above GW...the same power setting will normally be good for S speed.when Flap 1 is selected. when glide becomes activ, select flaps 2 and gear.
keep this power setting and allow the a/c to slow. .About one dot below glide select flaps 3 then select Flaps Full as you intercept the glideslope at the Vapp target.
Usually only small amounts of thrust changes are necessary but if you need it then adjust thrust sooner rather than later, obviously.

[dream747]

I had the opportunity on my previous flights to try out what we've discussed here so far. Apparently, a lower speed has priority over the profile in managed descent. What I did was select a speed of 230 knots and the aircraft simply pitches up to reduce the speed and continues deviating to get high on the profile, just as it would in an open descent.

[Microburst2002]

dream 747 thanks for your experiment

the principle of the 320's AFS is that always someone is in charge of speed, except in DES mode when speed is allowed to float about the target, within the magenta margins.

If with thrust idle a/thr mode on pitch maintained the profile, then "nobody" would be in charge of speed.

I assume that THR IDLE was green in your FMA, right?

[dream747]

Microburst, yes, THR IDLE was on the FMA throughout. On that particular day ATC needed us to reach a waypoint at a certain time, which we could only do so if we reduce our speed considerably. However we were only told after our original TOD point based on the FMGS descent speed. We went for managed descent (since we were still on FPR), and selected 230 knots. The aircraft simply pitched up and deviated from the profile while continuing it's descent on 230 knots. Eventually the 'More Drag' message came up on the FMGS. That's the whole story.

I think you have summed it up perfectly. Thanks for the interesting and fruitful discussion guys.