what are some calculations for planning your descent using mileage? i know some guys like to use timing which i think isnt that good an idea if you're losing lots of altitude.
i use 3 X altitude you want to loose and then take 1/2 your ground speed and add a zero (ex. 300 KIAS = 1500 ft/min)..
heard there are some other ways of doubling your altitude and descending at 2500 ft/min. (ex. 10,000 ft to lose, start back 20 miles back and descend at 2500 ft/min.
any others??
planning your descent from altitude
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Dust Devil
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Re: planning your descent from altitude
My ears just started to hurt.ug wrote:what are some calculations for planning your descent using mileage? i know some guys like to use timing which i think isnt that good an idea if you're losing lots of altitude.
i use 3 X altitude you want to loose and then take 1/2 your ground speed and add a zero (ex. 300 KIAS = 1500 ft/min)..
heard there are some other ways of doubling your altitude and descending at 2500 ft/min. (ex. 10,000 ft to lose, start back 20 miles back and descend at 2500 ft/min.
any others??
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Flying Nutcracker
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COCO THE MONKEY
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Depends whether pressurized, turbine etc....
Roughly, start 100 back from FL 410, 50 back from FL 200.. if presssurized turbine as a rule of thumb. Light jets and turboprops (Lear, King Air) seem to burn least fuel this way per article years ago in Pro Pilot. Seemed to work great for us. Shallower gradients cost more fuel.
If you were fast piston (say 250 GS) but unpresssurized, for example, I can see a more gentle gradient as suggested by ug for passenger comfort using 50 back from 10,000 giving just under 1000 fpm. The fuel cost penalty of pistons at lower altitude is small relative to turbine.
Roughly, start 100 back from FL 410, 50 back from FL 200.. if presssurized turbine as a rule of thumb. Light jets and turboprops (Lear, King Air) seem to burn least fuel this way per article years ago in Pro Pilot. Seemed to work great for us. Shallower gradients cost more fuel.
If you were fast piston (say 250 GS) but unpresssurized, for example, I can see a more gentle gradient as suggested by ug for passenger comfort using 50 back from 10,000 giving just under 1000 fpm. The fuel cost penalty of pistons at lower altitude is small relative to turbine.
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marktheone
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There are many general rules of thumb.
This is just another one that works for me. I use it to cross check what the VNAV is telling me to determine if it is giving good info.
- Altitude X 3
- plus or minus 1 mile for every ten knots of head wind or tail wind
- increase by 25% for the amount of the descent will have engine anti-ice on.
- plus deceleration at 10000 feet from descent speed to 250 knots (varies with aircraft types and how aerodymanically clean they are... can range from 1 mile to 2 miles for every ten knots of deceleration... ie. is the engine-anti-ice on or off?)
So 41000 feet descent X 3 = 123 miles (123)
40 knot head wind = - 4 miles (119)
Engine anti Ice on from FL 200 to 8000'
= 12000' x .25 = 3000' X 3 = 9 miles (128)
10000' deceleration 300Kts-250Kts:
50Kts deceleration X 1 = 5 miles (133)
Or (with Eng A/I on)
50 Kts deceleration X 2 = 10 miles (138)
Another factor to consider is the weight of the aircraft.
there will be a decrement or an addition if the aeroplane is very light or very heavy. = +/- (XX) miles
As you are in descent monitor your position relative to your planned profile. Things somestimes work out perfect... and other times they do not go to plan.
Generally I find with aircraft that are aerodynamically clean (and do not like to decelerate quickly), plan to be at 10,000' at 40NM from EOD (assuming EOD is at sealevel of course) and you should have plenty room to adjust for any short gate vectoring that may come your way.
This is just another one that works for me. I use it to cross check what the VNAV is telling me to determine if it is giving good info.
- Altitude X 3
- plus or minus 1 mile for every ten knots of head wind or tail wind
- increase by 25% for the amount of the descent will have engine anti-ice on.
- plus deceleration at 10000 feet from descent speed to 250 knots (varies with aircraft types and how aerodymanically clean they are... can range from 1 mile to 2 miles for every ten knots of deceleration... ie. is the engine-anti-ice on or off?)
So 41000 feet descent X 3 = 123 miles (123)
40 knot head wind = - 4 miles (119)
Engine anti Ice on from FL 200 to 8000'
= 12000' x .25 = 3000' X 3 = 9 miles (128)
10000' deceleration 300Kts-250Kts:
50Kts deceleration X 1 = 5 miles (133)
Or (with Eng A/I on)
50 Kts deceleration X 2 = 10 miles (138)
Another factor to consider is the weight of the aircraft.
there will be a decrement or an addition if the aeroplane is very light or very heavy. = +/- (XX) miles
As you are in descent monitor your position relative to your planned profile. Things somestimes work out perfect... and other times they do not go to plan.
Generally I find with aircraft that are aerodynamically clean (and do not like to decelerate quickly), plan to be at 10,000' at 40NM from EOD (assuming EOD is at sealevel of course) and you should have plenty room to adjust for any short gate vectoring that may come your way.
Last edited by wsguy on Thu Jan 12, 2006 3:30 pm, edited 1 time in total.
I use 3X the altitude to lose and 5X the ground speed for rate of descent for steam-powered a/c, and VNAV for the rest. W/x, traffic, passengers, fuel loading notwithstanding.
Using G/S, you don't have to worry 'bout the winds.
Using G/S, you don't have to worry 'bout the winds.
"What's it doing now?"
"Fly low and slow and throttle back in the turns."
"Fly low and slow and throttle back in the turns."
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Rubberbiscuit
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When destination disappears under the nose, time to chop and drop.
Actually,first rule is to convert groundspeed into miles per minute and then determine Time to descend. Airplane for unpressurized and cabin altitude for pressurized.
Actually,first rule is to convert groundspeed into miles per minute and then determine Time to descend. Airplane for unpressurized and cabin altitude for pressurized.
The average pilot, despite the somewhat swaggering exterior, is very much capable of such feelings as love, affection, intimacy and caring.
These feelings just don't involve anyone else.
These feelings just don't involve anyone else.
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Cargo Pilot
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Holy crap people. Why do some pilots have to make simple things sound so f%$^ing difficult. My opinion, all of these formulas are definitely not coming from pilots that actually fly real passengers or cargo for a living 
.
Keep it simple stupid. Marktheone and oldtimer have it right. Know your bird and time your descent.
God I feel like smackin' someone...
.Keep it simple stupid. Marktheone and oldtimer have it right. Know your bird and time your descent.
God I feel like smackin' someone...
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ditshisturber
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Cargo Pilot wrote:...My opinion, all of these formulas are definitely not coming from pilots that actually fly real passengers or cargo for a living
Keep it simple stupid. Marktheone and oldtimer have it right. Know your bird and time your descent.
God I feel like smackin' someone...
I think you should reconsider your initial comment. I think the formulas may offer you more insight on WHY the answer comes about... You can't "get to know your bird" by simply guessing each time... If you understand the basic formulas and how a simple few steps of thinking can enhance efficiency (like a constant rate of descent and groundspeed factors). All of these methods work for different situations, but the end results are all the same... remove the guesswork when you don't have the answer to "when should I start down?"
'simple things?'Cargo Pilot wrote:Holy crap people. Why do some pilots have to make simple things sound so f%$^ing difficult. My opinion, all of these formulas are definitely not coming from pilots that actually fly real passengers or cargo for a living
Keep it simple stupid. Marktheone and oldtimer have it right. Know your bird and time your descent.
God I feel like smackin' someone...
listen chief. i don't know how much your 152 costs per hour, but when you start flying heavy metal around the sky you'll appreciate saving that extra 0.1 on the air time by planning your descent properly.
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Cargo Pilot
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You think I'm guessing? I take my flying very seriously and there is no room for guessing or 'gee golly gosh, I sure hope this works...'
Go ahead genius, use your formulas. My point was there is a better way.
My God man - are you really saying this is the best way;
The real issue here is that some people feel the need to complicate things in order to make themselves feel more intelligent. I don't understand it, but then again, I don't have a small penis...
Go ahead genius, use your formulas. My point was there is a better way.
My God man - are you really saying this is the best way;
Who the hell does that? Time it time it time it. It's incredibly f#$%ing simple and I know without a doubt that it works.- Altitude X 3
- plus or minus 1 mile for every ten knots of head wind or tail wind
- increase by 25% for the amount of the descent will have engine anti-ice on.
- plus deceleration at 10000 feet from descent speed to 250 knots (varies with aircraft types and how aerodymanically clean they are... can range from 1 mile to 2 miles for every ten knots of deceleration... ie. is the engine-anti-ice on or off?)
So 41000 feet descent X 3 = 123 miles (123)
40 knot head wind = - 4 miles (119)
Engine anti Ice on from FL 200 to 8000'
= 12000' x .25 = 3000' X 3 = 9 miles (128)
10000' deceleration 300Kts-250Kts:
50Kts deceleration X 1 = 5 miles (133)
Or (with Eng A/I on)
50 Kts deceleration X 2 = 10 miles (138)
The real issue here is that some people feel the need to complicate things in order to make themselves feel more intelligent. I don't understand it, but then again, I don't have a small penis...
Last edited by Cargo Pilot on Thu Jan 12, 2006 9:52 pm, edited 1 time in total.
I gotta say guys... I have seen a lot of descent planning. 3x alt or 2x alt + 10nm works well in most jets. Yes vnav works too... I have always used 2x alt + 10nm it keeps you calculating every 10000ft and you are always in the loop. for you low level cargo guys. descent planning has a bit to do with passenger comfort but more to do with trying to guess what ATC is planning in the future for you. Coming form the south into YYZ they like to drop you down about 150 nm back, depending on the day. For the busier bits of airspace...do what you are told!
My good colleage Mr. Cargo Pilot.
I think you have missed the point of my post. I meant it to be more of a technical break down of factors to consider. You go ahead with what works for you in your operations... I am not telling you how to fly your airplane.
We all are looking for that efficient descent that saves fuel and time... to fly efficiently. Nothing more rewarding to a professional than to arrive with a smaller fuel burn than planed.
There are lot's of options you can choose. You can just blindly follow VNAV if you fly such a machine so equipped. You can just go Alt X3 plus 10 miles to to plan a TOD.
However... there are other fators to consider. I did not post this to complicate a very simple process. What I was doing is highlighting some of the other factors that may need to be considered. IF you fly an older A/C that does not flatten out the descent rate when EAI is selected... then obviously you will not have to factor that one in. (although every jet I have flown requires that the idle thrust be increased depending on the TAT) Same goes for head wind / tail wind correction.... certainly ground speed will help you to determine that one also. If you simply go ALT multiplied by three and do not consider your head wind(which will become obvious by the resultant ground speed.) ... the net result may very well be that you will spend a lot of time down low burning up fuel getting to the airport.
Am I saying that using these formula's are the best way? I am saying this. Know your airplane and it's characteristics.
If you go simply by time... you will not always get the same indicated airpeed for the targeted rate of descent. Which means that you may not always be flying at the most efficient indicated airpeed.
With an airliner, the sooner one can have the thrust at flight idle the less fuel you will burn. You could be burning 6 tones an hour in cruise as oppossed to 1.5 tonnes an hour at flight idle.
The problem is often what ATC wants for a descent schedule. If you plan for a M.8/320 transition speed... you will save time...your burn will be higher. Or if you go with a M.78/289 transition speed, your burn will be less. Often ATC will request a 300KT transition speed. (depending on the aircraft type your are flying of course.
So by going with strictly by time and a Rate of Descent with a heavy jet, you may or may not be at the most fuel efficient speed. Not to forget to mention also that the difference in the aircraft's weight (from heavy to light) will also have a bearing on what the most efficient speed schedule is.
Timing is a nice simple way to do things.... but not always the most efficient for all aircraft types.
Now The above factors to consider are not from my intelligence or lack of manhood as you so articulately put it. (I am surprised at the absolute hostility of your tone.... you are taking this to a dimension that is beyond my intention for this post of mine to go.) I have been shown these very things from past training departments with CAR705 carriers I have flown with in the past. I have been given referrence material from United as well as from British Airways on this very subject.
Perhaps their penis size and intellect is also worthy of your assessment.
SO if I may put this in context...
These are some things that can to be considered... depends on the type you are flying.
Oh and by the way, I do fly people and cargo for a living and hold nine type ratings between Airbus and Boeing.... One last thought... My post was not directed to you in any way. Not sure how you think I am saying you are guessing... or how it is you are antagonized by my post.
As I said earlier, do what works for you in your operation. Not telling you how to fly your airplane. I never fly a light twin like a widebody. Each aircraft has it's own characteristics. And I fly them accordingly.
I'll leave this post at this point.
I am open to share technical points and news on this forum. However I choose not to bring it to a personal level as you have.....
Happy flying
I think you have missed the point of my post. I meant it to be more of a technical break down of factors to consider. You go ahead with what works for you in your operations... I am not telling you how to fly your airplane.
We all are looking for that efficient descent that saves fuel and time... to fly efficiently. Nothing more rewarding to a professional than to arrive with a smaller fuel burn than planed.
There are lot's of options you can choose. You can just blindly follow VNAV if you fly such a machine so equipped. You can just go Alt X3 plus 10 miles to to plan a TOD.
However... there are other fators to consider. I did not post this to complicate a very simple process. What I was doing is highlighting some of the other factors that may need to be considered. IF you fly an older A/C that does not flatten out the descent rate when EAI is selected... then obviously you will not have to factor that one in. (although every jet I have flown requires that the idle thrust be increased depending on the TAT) Same goes for head wind / tail wind correction.... certainly ground speed will help you to determine that one also. If you simply go ALT multiplied by three and do not consider your head wind(which will become obvious by the resultant ground speed.) ... the net result may very well be that you will spend a lot of time down low burning up fuel getting to the airport.
Am I saying that using these formula's are the best way? I am saying this. Know your airplane and it's characteristics.
If you go simply by time... you will not always get the same indicated airpeed for the targeted rate of descent. Which means that you may not always be flying at the most efficient indicated airpeed.
With an airliner, the sooner one can have the thrust at flight idle the less fuel you will burn. You could be burning 6 tones an hour in cruise as oppossed to 1.5 tonnes an hour at flight idle.
The problem is often what ATC wants for a descent schedule. If you plan for a M.8/320 transition speed... you will save time...your burn will be higher. Or if you go with a M.78/289 transition speed, your burn will be less. Often ATC will request a 300KT transition speed. (depending on the aircraft type your are flying of course.
So by going with strictly by time and a Rate of Descent with a heavy jet, you may or may not be at the most fuel efficient speed. Not to forget to mention also that the difference in the aircraft's weight (from heavy to light) will also have a bearing on what the most efficient speed schedule is.
Timing is a nice simple way to do things.... but not always the most efficient for all aircraft types.
Now The above factors to consider are not from my intelligence or lack of manhood as you so articulately put it. (I am surprised at the absolute hostility of your tone.... you are taking this to a dimension that is beyond my intention for this post of mine to go.) I have been shown these very things from past training departments with CAR705 carriers I have flown with in the past. I have been given referrence material from United as well as from British Airways on this very subject.
Perhaps their penis size and intellect is also worthy of your assessment.
SO if I may put this in context...
These are some things that can to be considered... depends on the type you are flying.
Oh and by the way, I do fly people and cargo for a living and hold nine type ratings between Airbus and Boeing.... One last thought... My post was not directed to you in any way. Not sure how you think I am saying you are guessing... or how it is you are antagonized by my post.
As I said earlier, do what works for you in your operation. Not telling you how to fly your airplane. I never fly a light twin like a widebody. Each aircraft has it's own characteristics. And I fly them accordingly.
I'll leave this post at this point.
I am open to share technical points and news on this forum. However I choose not to bring it to a personal level as you have.....
Happy flying
Last edited by wsguy on Fri Jan 13, 2006 2:19 am, edited 4 times in total.
If I’m tight for fuel I use a steep low power descent, IE I’m at FL260, at 13 /mins back I start down at 2000' /min and just enough power to maintain the cabin scheduling a descent about 600 FT/LBS in a king air.
Normally I use the timing method (I find this very accurate when setting landing power at top of the descent and not touching it until the wheels touch the ground).
Whatever works for you; 3 times your attitude, time, whatever, as long as you consistent and accurate.
Cheers.
Normally I use the timing method (I find this very accurate when setting landing power at top of the descent and not touching it until the wheels touch the ground).
Whatever works for you; 3 times your attitude, time, whatever, as long as you consistent and accurate.
Cheers.
The feet you step on today might be attached to the ass you're kissing tomorrow.
Chase lifestyle not metal.
Chase lifestyle not metal.
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Dust Devil
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Um....... Nevermind 
cargo pilot has it right. Timing is ALWAYS the most efficient way to get down(other than VNAV), and with GPS the timing is always right. Just redo it quickly in your head on descent-the groundspeed is right on as well, so it is a matter of TIMING. You can adjust your rate of descent to whatever makes you happy with timing, eg 2000, 3000, 5000 fpm. It makes absolutely no sense to follow a 3 degree slope until you are on final, IMHO.
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Gurundu the Rat
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Fanspeed has it right, get to know your aircraft. If you fly a jet just find out what rate of descent you get at flight idle and time it. Keep a few miles to descelerate at 10000 ft and keep in mind that TAS will slowly drop in the descent. If done right you can usually keep it at flight idle all the way down till you configure for landing.
VNAV (sux) doesn't factor in the fact that TAS decreases in the descent and will get you down too early most of the time. Or if you are following a constant descent angle you will have to add power.
VNAV (sux) doesn't factor in the fact that TAS decreases in the descent and will get you down too early most of the time. Or if you are following a constant descent angle you will have to add power.
Cargo Pilot
While I am all for "keeping it simple" the fact is, it is not always that simple. In aviation we tend to all have certain formulas, rule of thumb, etc that we use, and we use them for a reason, because they "simplify" what we are trying to achieve.
With regards to descent planning ( and you can guess the aircraft I fly from my username) we use the basic times x3 + 10, the 10 dme allowing a speed reduction from 300 to 250 at 10. This is a very simple calculation, and it allows for a planning point to start, nothing more, you can "guess" all day, but you use an educated guess and this formula is the basis of the educated guess. You can then very simply vary your profile by recomputing on the way down via DME reference, relative to points you wish to achieve levels by. I operate mainly in European airspace, but also many other regions on a regular basis, North America, Far East, Africa, etc. and about 70 percent of the time ATC will give you descent before you ask anyway, but you have the point in your mind regardless. And they tend to control your profile anyway. You may have gates to reach, and x3 is the best guide to achieve these gates. While we use as a "rule" 10 to slow down, the reality is this works nicely with a VS of 1000 out of 11 and you generally make it with 2 to spare, but it is also easy to set 200 ROD at 11 and slow in 4DME, so it is always variable, but you must know what you are trying to achieve.
But planning is the key, because lets face it, ATC will judge your performance by what they observe, and you need to plan to achieve these goals and therefore conform to the ATC environment you operate in.
I can assure you that when you descend into LHR, FRA, AMS, CDG, HKG, JFK, etc you do not have the luxury of "guessing"
I would suggest that such a cavalier attitude as you have demonstrated would not be well received by any training Cpt should you end up in the RHS of a heavy jet, perhaps you should just sit back and read what has been written here, it is real world stuff, and there are some valid points. To minimize and scoff at them merely exposes the level of aviation you operate in.
Cheers
While I am all for "keeping it simple" the fact is, it is not always that simple. In aviation we tend to all have certain formulas, rule of thumb, etc that we use, and we use them for a reason, because they "simplify" what we are trying to achieve.
With regards to descent planning ( and you can guess the aircraft I fly from my username) we use the basic times x3 + 10, the 10 dme allowing a speed reduction from 300 to 250 at 10. This is a very simple calculation, and it allows for a planning point to start, nothing more, you can "guess" all day, but you use an educated guess and this formula is the basis of the educated guess. You can then very simply vary your profile by recomputing on the way down via DME reference, relative to points you wish to achieve levels by. I operate mainly in European airspace, but also many other regions on a regular basis, North America, Far East, Africa, etc. and about 70 percent of the time ATC will give you descent before you ask anyway, but you have the point in your mind regardless. And they tend to control your profile anyway. You may have gates to reach, and x3 is the best guide to achieve these gates. While we use as a "rule" 10 to slow down, the reality is this works nicely with a VS of 1000 out of 11 and you generally make it with 2 to spare, but it is also easy to set 200 ROD at 11 and slow in 4DME, so it is always variable, but you must know what you are trying to achieve.
But planning is the key, because lets face it, ATC will judge your performance by what they observe, and you need to plan to achieve these goals and therefore conform to the ATC environment you operate in.
I can assure you that when you descend into LHR, FRA, AMS, CDG, HKG, JFK, etc you do not have the luxury of "guessing"
I would suggest that such a cavalier attitude as you have demonstrated would not be well received by any training Cpt should you end up in the RHS of a heavy jet, perhaps you should just sit back and read what has been written here, it is real world stuff, and there are some valid points. To minimize and scoff at them merely exposes the level of aviation you operate in.
Cheers
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Jaques Strappe
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Holy Crap
I have never seen so many long winded formulas for planning a decent profile. When do you sart planning it? At rotation? I am not the best at math so I would be long past my alternate before I figured some of these things out!
There is so much to be said for keeping it simple! It isn't rocket science and there is no need to turn it into rocket science either.
I have never seen so many long winded formulas for planning a decent profile. When do you sart planning it? At rotation? I am not the best at math so I would be long past my alternate before I figured some of these things out!
There is so much to be said for keeping it simple! It isn't rocket science and there is no need to turn it into rocket science either.
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