THR IDLE / OP DES TOD Calculation
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THR IDLE / OP DES TOD Calculation
G'day jet drivers,
I'm interested in the finer points in calculating the TOD for a Thrust Idle, Open Descent - with spoil up at 1000'AGL.
So far, I know the basics based on a 0.78/300kt descent:
3 times height to lose, then;
add 5nm to slow down, then;
add 1.5nm for every 10kts of tailwind or,
subtract 1.0nm for every 10kts of headwind, then;
add or subtract 1.0nm for ever tonne above or below 60.0t LW.
Then monitor on the way down, adjust as required (using speed or brakes)
What are the calculations for:
Changes in QNH from datum of 1013
Changes in SPD from datum 0.78/300kts
Others?
go_soaring! instead
I'm interested in the finer points in calculating the TOD for a Thrust Idle, Open Descent - with spoil up at 1000'AGL.
So far, I know the basics based on a 0.78/300kt descent:
3 times height to lose, then;
add 5nm to slow down, then;
add 1.5nm for every 10kts of tailwind or,
subtract 1.0nm for every 10kts of headwind, then;
add or subtract 1.0nm for ever tonne above or below 60.0t LW.
Then monitor on the way down, adjust as required (using speed or brakes)
What are the calculations for:
Changes in QNH from datum of 1013
Changes in SPD from datum 0.78/300kts
Others?
go_soaring! instead
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This sounds like trying to find the hardest possible way to perform a simple task!
You can't be a real pilot, if you were you would know that the computer calculates all that stuff for you and just tells you when to start down...
If you haven't got a computer-driven aircraft, just use the First Officer...
You can't be a real pilot, if you were you would know that the computer calculates all that stuff for you and just tells you when to start down...
If you haven't got a computer-driven aircraft, just use the First Officer...
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What?!
Oh mate, why not make it hard for yourself and do Sudoku on the descent as well!?
There are 2 easy ways that I use, 4 x height for a gross error check for TOD, then use that down to FL150, its accurate enough. From that point use 3 x height, plus 1 track mile per 10knots of slowdown to 150kts, ie from 300 to 150 is 15 track miles, 250 to 150 is 10miles etc.....Too easy.
Or, multiply your track miles to run by 3, and subtract either 3000 feet from the total from 300kts, 2000feet from 250, and 1000 feet from 200 to Green Dot for the slowdown...easy.
There are 2 easy ways that I use, 4 x height for a gross error check for TOD, then use that down to FL150, its accurate enough. From that point use 3 x height, plus 1 track mile per 10knots of slowdown to 150kts, ie from 300 to 150 is 15 track miles, 250 to 150 is 10miles etc.....Too easy.
Or, multiply your track miles to run by 3, and subtract either 3000 feet from the total from 300kts, 2000feet from 250, and 1000 feet from 200 to Green Dot for the slowdown...easy.
A lot depends on the airport and runway you are going to. If you are going straight in on a runway aligned with your track you need to be very accurate to get down and reduce speed correctly.
Different story if you need to do a 180 turn for final. ATC will play a big part as well possibly holding you high, giving you vectors all over the place for seperation or calling for an early speed reduction when you had counted on diving the height off.
Asking for track miles will give a good idea of how the descent is progressing. Judgment and experience come in as well, if you are 5000' at 15 miles doing 250kts speed brakes or early gear extension will be required. Same conditions but green dot speed will only require flap and gear at the normal times.
Each approach and landing is different, that's why we are paid the mega salaries.
Different story if you need to do a 180 turn for final. ATC will play a big part as well possibly holding you high, giving you vectors all over the place for seperation or calling for an early speed reduction when you had counted on diving the height off.
Asking for track miles will give a good idea of how the descent is progressing. Judgment and experience come in as well, if you are 5000' at 15 miles doing 250kts speed brakes or early gear extension will be required. Same conditions but green dot speed will only require flap and gear at the normal times.
Each approach and landing is different, that's why we are paid the mega salaries.
THR IDLE /OP DES (same as flight level change in the boeing, SPEED / DES is the same as VNAV) makes it a bus, and the .78 would make it a minibus i would think so a 320?
Now Metro if you can land one from 15nm 5000' and 250kts straight in your a far better driver than I. Unless these minibuses slow and go down a lot better than their larger cousins. A 330/340 would need to be 20nm min to make that work, most would stick to 25nm.
I do it like nosegear but use the 4 times table to 10000 and then swap to the 3 times table with adjustment for speed, if at 250kts would add 5nm if 210kts and flap1 would add 3nm, if 180kts flap 2 would stay on the 3 times profile.
The Bus FMC uses a level segment to slow down, so to fly a continuous descent approach its profile is not accurate in the later parts of the descent.
Now Metro if you can land one from 15nm 5000' and 250kts straight in your a far better driver than I. Unless these minibuses slow and go down a lot better than their larger cousins. A 330/340 would need to be 20nm min to make that work, most would stick to 25nm.
I do it like nosegear but use the 4 times table to 10000 and then swap to the 3 times table with adjustment for speed, if at 250kts would add 5nm if 210kts and flap1 would add 3nm, if 180kts flap 2 would stay on the 3 times profile.
The Bus FMC uses a level segment to slow down, so to fly a continuous descent approach its profile is not accurate in the later parts of the descent.
Thrpttle idle/open descent.....WTF.
Is there a closed descent, or a half open half closed descent. Or maybe an almost closed ....but just a touch open descent. Like why do they have t make it so effing complicated. It seems these days one needs a phd in compters and the ability to type at 80 words per minute just to taxi the buggers.
God forbid, you have 13 modes for descent, god knows how many for climb and cruise...........But can it make a decent coffee......see not so smart afterall.
Does anyone know where to buy a copy of Avionics for dummies.
Is there a closed descent, or a half open half closed descent. Or maybe an almost closed ....but just a touch open descent. Like why do they have t make it so effing complicated. It seems these days one needs a phd in compters and the ability to type at 80 words per minute just to taxi the buggers.
God forbid, you have 13 modes for descent, god knows how many for climb and cruise...........But can it make a decent coffee......see not so smart afterall.
Does anyone know where to buy a copy of Avionics for dummies.
4 Descent modes on the A320
DES - means the aircraft will follow the plan ie speeds and heights at various way points will followed.
OPEN DES - Power back, aircraft drops. Same as C152
VS - Feet per minute rate of descent. Usefull if instructed to descend early by ATC, give them 500' per minute
FPA - Flight Path Angle, fly a 3 degree descent for an instrument approach.
If you want complication look up "mode reversions"
I wouldn't fancy doing it straight in, but from a 90 degree angle autopilot out and as much speed brake as VLS would allow followed by an early gear extension could be do able depending on weight and headwind.
Must remember to note the exact figures next time ATC give us a short cut.
DES - means the aircraft will follow the plan ie speeds and heights at various way points will followed.
OPEN DES - Power back, aircraft drops. Same as C152
VS - Feet per minute rate of descent. Usefull if instructed to descend early by ATC, give them 500' per minute
FPA - Flight Path Angle, fly a 3 degree descent for an instrument approach.
If you want complication look up "mode reversions"
Now Metro if you can land one from 15nm 5000' and 250kts straight in your a far better driver than I.
Must remember to note the exact figures next time ATC give us a short cut.
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All good answers, but not quite what I'm looking for. If there's any ex-Ansett drivers reading, and if you can remember the calculations, then I'd love to hear from you!
Those who have answered, cheers. Obviously in the end, it's just an aircraft, nothing hard, just fly it! One of the problems with the Airbus (probably all jets for that matter!), is that there seems to be many different ways to fly the approach for example. 20nm @ 250kts, manage speed and pull for THR IDLE / OP DES will get you to 1000' before getting the jets to spoil up. You can also drive it in at 250kts, level it up, manage speed, wait for the G/S intercept and hey presto, same result. You can leave the A320 in managed mode, and it'll do a beautiful job if you've put all the correct constraints (ALT's and SPD's) in (albeit slightly inefficient). You can...
Though the question I was asking was for the finer calculations in calculating a TOD point (obviously the QNH one is taking it a bit far, but if there is something for it, then why not arm yourself with the knowledge?). That's all. Not interested in re-fining the profile once on DES, or how to fly the approach. I understand that this changes daily, ATC, more/less wind than estimated, error in calculations, etc.
go_soaring! instead
Those who have answered, cheers. Obviously in the end, it's just an aircraft, nothing hard, just fly it! One of the problems with the Airbus (probably all jets for that matter!), is that there seems to be many different ways to fly the approach for example. 20nm @ 250kts, manage speed and pull for THR IDLE / OP DES will get you to 1000' before getting the jets to spoil up. You can also drive it in at 250kts, level it up, manage speed, wait for the G/S intercept and hey presto, same result. You can leave the A320 in managed mode, and it'll do a beautiful job if you've put all the correct constraints (ALT's and SPD's) in (albeit slightly inefficient). You can...
Though the question I was asking was for the finer calculations in calculating a TOD point (obviously the QNH one is taking it a bit far, but if there is something for it, then why not arm yourself with the knowledge?). That's all. Not interested in re-fining the profile once on DES, or how to fly the approach. I understand that this changes daily, ATC, more/less wind than estimated, error in calculations, etc.
go_soaring! instead
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Well I prefer to disconnect autothrottle and idle the ba$tard then just fly the gates, forget autopilot modes they are just secondary. Any real pilot can pretty much tell the profile using the DME and distance, jeez it is not rocket science. But asking for details will depend on aircraft type so I cant tell you about the computer Airbus, I prefer to use my head!
A rough estimate without scientific formulae will be better than a managed descent anytime. Then there is the speedbrake, which will always correct any high energy descent!.
Better lay down now, feel exhausted with all this theory.
Better lay down now, feel exhausted with all this theory.
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go soaring, maybe if you posted exactly what your after you'll get your answer. You asked for TOD calcs and then proceeded to give all kinds of ways to scratch an itch, but then say it's not what your after.
There is no problem with an Airbus in descent, it does a fine job of it, but your the pilot, so you need to have a way of backing up and checking what it's doing. All the Airbus family, as I'm sure the Boeing, will all do Managed approaches with constraints very well. The constraints are not "put in" but are part of the database which you must check, there is certainly nothing "inefficient" about that. What is inefficient is QNH adjustments at TOD while 140NM out Or, "driving it in level"..now that's inefficient in a jet. Your TOD calc is the least of your worries really, refining the descent is the trick, with due regard to winds, ATC, traffic, track shortening etc etc.
I personally have never heard of QNH corrections to TOD, after all, your in Standard, so how that could affect your TOD I have no idea. But then, if your doing your proper descent calcs, you'll catch that at Transition. Quite apart from it can't be more than a few hundred feet.
Maybe just let the prooners know what how you want to "arm" yourself with said knowledge might help.
Nosey
There is no problem with an Airbus in descent, it does a fine job of it, but your the pilot, so you need to have a way of backing up and checking what it's doing. All the Airbus family, as I'm sure the Boeing, will all do Managed approaches with constraints very well. The constraints are not "put in" but are part of the database which you must check, there is certainly nothing "inefficient" about that. What is inefficient is QNH adjustments at TOD while 140NM out
Or, "driving it in level"..now that's inefficient in a jet. Your TOD calc is the least of your worries really, refining the descent is the trick, with due regard to winds, ATC, traffic, track shortening etc etc. I personally have never heard of QNH corrections to TOD, after all, your in Standard, so how that could affect your TOD I have no idea. But then, if your doing your proper descent calcs, you'll catch that at Transition. Quite apart from it can't be more than a few hundred feet.
Maybe just let the prooners know what how you want to "arm" yourself with said knowledge might help.
Nosey
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Cheers NoseGear, I was starting to think that's what I'll have to do. Will give it some thought overnight and try again tomorrow...
go_soaring! instead
go_soaring! instead
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Keep it simple....
TOPD = 3 times altitude + 10nm
On descent:
3 times track nm = Altitude (i.e 100nm = 30,000ft).
From 300 to 250kts I use 1000ft and from 250 to flaps up I use another 1000ft.
Therefore, at 100nm doing 300kts I want to be 30,000ft - 1000 - 1000 = passing 28000ft. At 30nm 250kts I want to be 9000 - 1000 = 8000ft.
Gates:
10000ft, 250kts, 40nm
8000ft, 250kts, 30nm
5000ft, 250kts, 20nm
Obviously serious tailwinds/headwinds make a difference. I use 1000ft/20kts of wind.
Keep it simple.
TOPD = 3 times altitude + 10nm
On descent:
3 times track nm = Altitude (i.e 100nm = 30,000ft).
From 300 to 250kts I use 1000ft and from 250 to flaps up I use another 1000ft.
Therefore, at 100nm doing 300kts I want to be 30,000ft - 1000 - 1000 = passing 28000ft. At 30nm 250kts I want to be 9000 - 1000 = 8000ft.
Gates:
10000ft, 250kts, 40nm
8000ft, 250kts, 30nm
5000ft, 250kts, 20nm
Obviously serious tailwinds/headwinds make a difference. I use 1000ft/20kts of wind.
Keep it simple.
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What I'm trying to figure out is. We're sitting in cruise @ FL350 into a sea level aerodrome. The broken arrow (Airbus's calculated descent point) is indicating a managed descent @ 117nm from destination.
350 * 3 = 105nm
105 + 5nm to slow down = 110nm
I've predicted 20kts T/W on descent, so 110nm + (2 * 1.5) = 113nm
The a/c weighs 58t on LW, 113nm - 2nm = 111nm
So if I wanted pull for THR IDLE / OP DES, and keep it that way to the ground (all things being equal!), then the TOD point would be 111nm or 6nm past the Airbus A320's broken arrow.
What I want to know is.. if ATC says, 0.76/280kts. What do I then do to the 111nm calculated descent point. In this case, it's a slower descent, so I must (surely!) add (X)nm per every say 0.01/010kts for example.
The QNH thing is pedantic, but if there's a calculation out there for it, why not factor it in and try and nail it!
All the usual stuff of working around gates, and 3* profiles + whatever still stand, but I'm just trying to find that TOD point where I can pull for THR IDLE and start my descent. Obviously I'll be monitoring everything, if I notice we get lower, I'll adjust accordingly; if we get higher, I'll adjust accordingly. All I want is that initial TOD point, the rest I can figure out myself, adjust, use my experience, local knowledge, etc, to get to the goal: 1000' spool up!
go_soaring! instead
350 * 3 = 105nm
105 + 5nm to slow down = 110nm
I've predicted 20kts T/W on descent, so 110nm + (2 * 1.5) = 113nm
The a/c weighs 58t on LW, 113nm - 2nm = 111nm
So if I wanted pull for THR IDLE / OP DES, and keep it that way to the ground (all things being equal!), then the TOD point would be 111nm or 6nm past the Airbus A320's broken arrow.
What I want to know is.. if ATC says, 0.76/280kts. What do I then do to the 111nm calculated descent point. In this case, it's a slower descent, so I must (surely!) add (X)nm per every say 0.01/010kts for example.
The QNH thing is pedantic, but if there's a calculation out there for it, why not factor it in and try and nail it!
All the usual stuff of working around gates, and 3* profiles + whatever still stand, but I'm just trying to find that TOD point where I can pull for THR IDLE and start my descent. Obviously I'll be monitoring everything, if I notice we get lower, I'll adjust accordingly; if we get higher, I'll adjust accordingly. All I want is that initial TOD point, the rest I can figure out myself, adjust, use my experience, local knowledge, etc, to get to the goal: 1000' spool up!
go_soaring! instead
Don't get too hung up on descent points. Wind changes and atc will impact your profile more than the Baro ever will.
Pity you don't fly a classic 74... Just descend 20 mind after the f/e opens reserve 1&4!
Pity you don't fly a classic 74... Just descend 20 mind after the f/e opens reserve 1&4!
One of the problems with the Airbus (probably all jets for that matter!)