The Jacobson Flare ?
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To answer your question, click the link below.
http://www.pprune.org/forums/archive...p/t-14149.html
http://www.pprune.org/forums/archive...p/t-14149.html
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Never heard of this technique, Agreed it could well be a load of b@{{@(s but curiosity has got the better of me. could someone please enlighten me as to the procedure, Thanks
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Fly a stabilized approach,looking more and more outside as you get near the ground. At about the right height (visual cues and radio alt) you flare and land. Never been different. Mr.Jacobsen may have made someother contribution to aviation but this wasn't one of them. He should keep trying though.
I first read about and adopted the Jacobson Flare technique as a young private pilot, while eagerly building my hours up before taking on a commercial pilot licience. The year was 1987.
(In fact it was an article published in the Australian "Aviation Safety Digest" no.134 (Spring 1987). That edition was solely dedicated to the subject of landing. A post by Checkboard in the other thread highlighted by sander82 in this thread includes a copy of that very article. Unfortunately it is missing the diagrams which help explain the concept alot.)
Frankly i consider the Jacobson Flare to be THE best aviation tool I have ever learned! I can not recommend it highly enough. It has allowed me to flare and land every aeroplane I have flown, first time, every time, with confidence and consistancy! As an example, I remember using the formula on the B767-200 and the first time I flew the simulator, I landed it without any imput from the instructor. No floating, no over control, no doubt! Same thing again when I transferred to the B737.
019360 says:
"Fly a stabilized approach,looking more and more outside as you get near the ground. At about the right height (visual cues and radio alt) you flare and land. Never been different."
This is EXACTLY the sentiment Captain Jacobson is addressing. An excerpt from his article:
"Historically, instruction in determining a suitable and consistent flare point has been inadequate to say the least. We are attempting to recognize and extract one flare point from a range of acceptable flare circumstances. Generally, the best that instructors have been able to manage is to demonstrate a suitable flare point for a particular aircraft as being 'about here'.
The student pilot has no proper model except his memory, and that in itself is inconsistent. Trial and error are the arbiters in determining the soundness of his developing judgment. Unfortunately even after the basic skills are mastered, the problem still exists because every aircraft type requires a different flare height. as a pilot converts to successive aircraft types, he faces the same problem over and over. He has no proper model at the very time he needs one most, and there lies a clue."
The problem with "At about the right height (visual cues and radio alt) you flare and land." as espoused by 019360 and others is that the visual picture changes with runway slope and especially runway width. A 30 metre wide runway look very different to a standard 45 metre wide runway, which looks very different to a 60 metre wide runway.
At the correct flare height, the narrow 30 metre wide runway makes it look as though you are still too high to commence the flare. Invariably those waiting for the "right" visual cues or picture (based on a 45 metre wide runway) will flare too late and a very firm landing will often result.
The opposite happens if you are landing on a 60 metre wide runway. Again if you are waiting to see the right picture based on a 45 metre wide runway, you will invariably begin the flare too early, and a long landing will result.
The runway width is irrelevent to someone using the Jacobson Flare technique.
When you get down to it, the concepts are very basic and quite brilliant! You simply fly your eyes towards your chosen aiming point on the runway ( usually somewhere near the 1000 ft markers (300m from the threshold). When a pre-determined reference point on the runway centreline passes behind/beneith the aircraft's glareshield, that is the time to commence the flare. (This reference point is actually the point on the runway where the wheels would have hit the runway if there was no flare.)
It is brilliant because you are effectively determining the height above the runway to commence the flare without having to actually think about or try to estimate what the aircraft's height actually is! Instead it utilises basic triginometry ie "the branch of mathematics dealing with the relations of the sides and angles of triangles and with the relevant functions of any angles." so that you are only using horizontal distances along the runway instead. As a result, because the approach angle is 3 degress or 20:1, if you can discern a distance along the runway of 20 feet (6.1 metres) (about half the length of a single centreline marking) you can discern a flare height to within 1 ft!!!
Get it???
There are two formulas you can use. The first one is:
Reference Distance = [(60/Glide Path Angle) x (vertical height above mainwheels)] + horizontal distance of eyes from mainwheels.
For example: a light aircraft with the pilot's eyes 5 feet above the mainwheels and no significant horizontal distance between them -- on a 3 degree glide path angle:
Reference distance = 60/3 x 5 = 100 ft (30 metres)
So assuming you are flying an accurate 3 degree slope to your chosen aiming point on the runway, when a point on the runway surface 30 metres this side of your aiming point passes below your glareshield, it is time to tranfer your aiming point to the end of the runway and flare.
B747 = [(43 ft x 20) + 90 ft] = 950 ft
So if you are aiming for the 1500 ft markers, when the 500 ft markers disapear under the glareshield, it is time to flare.
Now this formula assumes that the glareshield cut-off angle is consistant between aircraft types, and apparenty they are remarkably similar.
There is another formula to refine this reference distance if you know the flare height desired by the manufacturers and you know the glareshield cut-off angle.
Again for the B747:
Height difference between pilot eyes and main wheels = 43 ft
Flare height above runway (main wheels) = 30 ft
Therefore eye height at flarepoint = 30+43= 73 ft.
Glareshield cut-off angle = 16 degrees.
Approach slope angle = 3 degrees.
Aimpoint distance from threshold = 1500 ft
Reference distance = 73 ft x (cot 3 - cot 16) = 73 x (19.08-3.49)
Reference distance = 1138 ft. Assume 1140 ft.
Now admittedly there is around 100 ft discrepancy between this distance and the first one. But if you divide 100 ft by 20, that is the actual discrepancy in terms of height. It's just 5 feet. At 750 ft/min that equates to 0.4 of a second! Split the difference if you like.
So 1500 - 1140 = 360 ft.
B747:When a point 360 ft beyond the threshold (140 ft prior to the 500 ft markers) passes below the glareshield and out of view, begin the flare.
For the B767:
Height difference between pilot eyes and main wheels = 30 ft
Flare height above runway (main wheels) = 25 ft
Therefore eye height at flarepoint = 30+25= 55 ft.
Glareshield cut-off angle = 17.5 degrees.
Approach slope angle = 3 degrees.
Aim point distance from threshold = 1150 ft
Reference distance = 55 ft x (cot 3 - cot 17.5) = 55 x (19.08-3.17)
Reference distance = 875 ft.
So 1150 - 875 = 275 ft
When a point 275 ft beyond the threshold (225 ft prior to the 500 ft marker) passes below the glareshield, it is time to flare.
B737-400 we shall use the first formula.
Height between eyes and main wheels = 17 ft
Distance between pilot eyes and main wheels = 46 ft
Glide slope = 3 degrees.
Aiming point distance from threshold= 1000 ft.
(17 x 20) + 46 = 386 ft ( Assumed 390 ft)
Reference point =1000 - 390 = 610 ft beyond the threshold.
Seeing as the 500 ft marker is around 100 ft (30 m) long and begins at the 500 ft point, you can safely say that the reference point is at the other end of the 500 ft marker.
I know this post is a long one but I really do feel it is worth exposing. For those non-believers, I simply ask you to take note of these reference points . Next time you are support pilot / Pilot Not Flying just notice when that point passes under the glareshield and how close it is to when the flare begins. Have a think about how easy it is to see it happening. It doesn't require you to look anywhere other than the runway centreline. In fact it doesn't even require you to take your eyes off the aiming point, just peripheral vision is enough, otherwise it is a minor and quick glance away from the aiming point at the most.
Regarding the actual flare, there was another brilliant article covering that topic in the same edition of the Aviation Safety Digest magazine. It prevented overcontrolling, over flaring, and allowed the aeroplane to almost land itself. I might paraphrase that if anyone is interested.
Cheers.
(In fact it was an article published in the Australian "Aviation Safety Digest" no.134 (Spring 1987). That edition was solely dedicated to the subject of landing. A post by Checkboard in the other thread highlighted by sander82 in this thread includes a copy of that very article. Unfortunately it is missing the diagrams which help explain the concept alot.)
Frankly i consider the Jacobson Flare to be THE best aviation tool I have ever learned! I can not recommend it highly enough. It has allowed me to flare and land every aeroplane I have flown, first time, every time, with confidence and consistancy! As an example, I remember using the formula on the B767-200 and the first time I flew the simulator, I landed it without any imput from the instructor. No floating, no over control, no doubt! Same thing again when I transferred to the B737.
019360 says:
"Fly a stabilized approach,looking more and more outside as you get near the ground. At about the right height (visual cues and radio alt) you flare and land. Never been different."
This is EXACTLY the sentiment Captain Jacobson is addressing. An excerpt from his article:
"Historically, instruction in determining a suitable and consistent flare point has been inadequate to say the least. We are attempting to recognize and extract one flare point from a range of acceptable flare circumstances. Generally, the best that instructors have been able to manage is to demonstrate a suitable flare point for a particular aircraft as being 'about here'.
The student pilot has no proper model except his memory, and that in itself is inconsistent. Trial and error are the arbiters in determining the soundness of his developing judgment. Unfortunately even after the basic skills are mastered, the problem still exists because every aircraft type requires a different flare height. as a pilot converts to successive aircraft types, he faces the same problem over and over. He has no proper model at the very time he needs one most, and there lies a clue."
The problem with "At about the right height (visual cues and radio alt) you flare and land." as espoused by 019360 and others is that the visual picture changes with runway slope and especially runway width. A 30 metre wide runway look very different to a standard 45 metre wide runway, which looks very different to a 60 metre wide runway.
At the correct flare height, the narrow 30 metre wide runway makes it look as though you are still too high to commence the flare. Invariably those waiting for the "right" visual cues or picture (based on a 45 metre wide runway) will flare too late and a very firm landing will often result.
The opposite happens if you are landing on a 60 metre wide runway. Again if you are waiting to see the right picture based on a 45 metre wide runway, you will invariably begin the flare too early, and a long landing will result.
The runway width is irrelevent to someone using the Jacobson Flare technique.
When you get down to it, the concepts are very basic and quite brilliant! You simply fly your eyes towards your chosen aiming point on the runway ( usually somewhere near the 1000 ft markers (300m from the threshold). When a pre-determined reference point on the runway centreline passes behind/beneith the aircraft's glareshield, that is the time to commence the flare. (This reference point is actually the point on the runway where the wheels would have hit the runway if there was no flare.)
It is brilliant because you are effectively determining the height above the runway to commence the flare without having to actually think about or try to estimate what the aircraft's height actually is! Instead it utilises basic triginometry ie "the branch of mathematics dealing with the relations of the sides and angles of triangles and with the relevant functions of any angles." so that you are only using horizontal distances along the runway instead. As a result, because the approach angle is 3 degress or 20:1, if you can discern a distance along the runway of 20 feet (6.1 metres) (about half the length of a single centreline marking) you can discern a flare height to within 1 ft!!!
Get it???
There are two formulas you can use. The first one is:
Reference Distance = [(60/Glide Path Angle) x (vertical height above mainwheels)] + horizontal distance of eyes from mainwheels.
For example: a light aircraft with the pilot's eyes 5 feet above the mainwheels and no significant horizontal distance between them -- on a 3 degree glide path angle:
Reference distance = 60/3 x 5 = 100 ft (30 metres)
So assuming you are flying an accurate 3 degree slope to your chosen aiming point on the runway, when a point on the runway surface 30 metres this side of your aiming point passes below your glareshield, it is time to tranfer your aiming point to the end of the runway and flare.
B747 = [(43 ft x 20) + 90 ft] = 950 ft
So if you are aiming for the 1500 ft markers, when the 500 ft markers disapear under the glareshield, it is time to flare.
Now this formula assumes that the glareshield cut-off angle is consistant between aircraft types, and apparenty they are remarkably similar.
There is another formula to refine this reference distance if you know the flare height desired by the manufacturers and you know the glareshield cut-off angle.
Again for the B747:
Height difference between pilot eyes and main wheels = 43 ft
Flare height above runway (main wheels) = 30 ft
Therefore eye height at flarepoint = 30+43= 73 ft.
Glareshield cut-off angle = 16 degrees.
Approach slope angle = 3 degrees.
Aimpoint distance from threshold = 1500 ft
Reference distance = 73 ft x (cot 3 - cot 16) = 73 x (19.08-3.49)
Reference distance = 1138 ft. Assume 1140 ft.
Now admittedly there is around 100 ft discrepancy between this distance and the first one. But if you divide 100 ft by 20, that is the actual discrepancy in terms of height. It's just 5 feet. At 750 ft/min that equates to 0.4 of a second! Split the difference if you like.
So 1500 - 1140 = 360 ft.
B747:When a point 360 ft beyond the threshold (140 ft prior to the 500 ft markers) passes below the glareshield and out of view, begin the flare.
For the B767:
Height difference between pilot eyes and main wheels = 30 ft
Flare height above runway (main wheels) = 25 ft
Therefore eye height at flarepoint = 30+25= 55 ft.
Glareshield cut-off angle = 17.5 degrees.
Approach slope angle = 3 degrees.
Aim point distance from threshold = 1150 ft
Reference distance = 55 ft x (cot 3 - cot 17.5) = 55 x (19.08-3.17)
Reference distance = 875 ft.
So 1150 - 875 = 275 ft
When a point 275 ft beyond the threshold (225 ft prior to the 500 ft marker) passes below the glareshield, it is time to flare.
B737-400 we shall use the first formula.
Height between eyes and main wheels = 17 ft
Distance between pilot eyes and main wheels = 46 ft
Glide slope = 3 degrees.
Aiming point distance from threshold= 1000 ft.
(17 x 20) + 46 = 386 ft ( Assumed 390 ft)
Reference point =1000 - 390 = 610 ft beyond the threshold.
Seeing as the 500 ft marker is around 100 ft (30 m) long and begins at the 500 ft point, you can safely say that the reference point is at the other end of the 500 ft marker.
I know this post is a long one but I really do feel it is worth exposing. For those non-believers, I simply ask you to take note of these reference points . Next time you are support pilot / Pilot Not Flying just notice when that point passes under the glareshield and how close it is to when the flare begins. Have a think about how easy it is to see it happening. It doesn't require you to look anywhere other than the runway centreline. In fact it doesn't even require you to take your eyes off the aiming point, just peripheral vision is enough, otherwise it is a minor and quick glance away from the aiming point at the most.
Regarding the actual flare, there was another brilliant article covering that topic in the same edition of the Aviation Safety Digest magazine. It prevented overcontrolling, over flaring, and allowed the aeroplane to almost land itself. I might paraphrase that if anyone is interested.
Cheers.
Last edited by Blip; 22nd Sep 2006 at 04:37. Reason: Minor punctuation corrections
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Sorry to step in with a bucket of cold water, but Jacobson flare? I thought this sort of stuff was fairly standard when you went on a type and learnt landing techniques? It's hardly groundbreaking or 'brilliant'. To apply it mechanically does seem over reliant on seat position/height and always being in the right slot approaching the flare, and maybe not relying enough on actually flying the plane as it is. How about varying landing flap positions with their different attitudes?
Might I recommend the 'Rainboe Rotate Technique'? At rotate speed, pull the stick back steadily, then a bit more for Mum as you approach 10 degrees.
Might I recommend the 'Rainboe Rotate Technique'? At rotate speed, pull the stick back steadily, then a bit more for Mum as you approach 10 degrees.
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Blip,
I know what you mean and I am sure that you can reduce lots of things we do by common sense and judgement to numbers and formulae. And that doesn't make such an exercise wrong....I just feel exhausted reading it. The flare height is simply the beginning of the task as far as I see it. Finessing the big girl down onto the RW is the harder bit. Though to be fair my beloved 777 is a pussy cat.
It probably just means I'm getting old but too many numbers frighten me a bit. I have seen guys where I work now (Asia) talk about X-wind landings as though they were brain surgery and to no great effect either. They work out the drift in degrees fromthe ATIS but don't look at the windsock.
I know what you mean and I am sure that you can reduce lots of things we do by common sense and judgement to numbers and formulae. And that doesn't make such an exercise wrong....I just feel exhausted reading it. The flare height is simply the beginning of the task as far as I see it. Finessing the big girl down onto the RW is the harder bit. Though to be fair my beloved 777 is a pussy cat.
It probably just means I'm getting old but too many numbers frighten me a bit. I have seen guys where I work now (Asia) talk about X-wind landings as though they were brain surgery and to no great effect either. They work out the drift in degrees fromthe ATIS but don't look at the windsock.
Rainboe thanks for those good questions.
Yes it does rely on a consistant approach path to the aiming point, but no more than any other approach.
Sometimes you do get a gust of wind or some thermal lifting at say 100 ft and suddenly find yourself aiming a little further down the runway than you would have liked, and don't have enough room left to get it back on the correct path to your original aiming point without risking an unacceptable increase in descent rate so close to the ground. In these cases I simply move the aiming point further down the runway that equates to a new 3 degree path to the runway surface (within reason of course) and move the reference point the same distance. With practice it becomes quite easy to do.
Regarding various flap setting. Yes you are correct that that will have an effect on the glareshield cuttoff angle. The change will be the same as the change in approach attitude. The actual change is usually only a couple of degrees. cot 2 degrees equates to about 20 ft in horizontal distance. 4 degrees in attitude change varies the reference distance by around 43 ft. 43/20 = 2. So a 4 degree change in approach attitude will change your flare height by only 2 feet.
Regarding seating position. In the aircraft I fly, there isn't that much room to manoeuvre. You have to sit high enough to see over the control column to the EHSI, but low enough that I my arm is not too high relative to the control wheel and my legs are comfortable on the rudder peddals.
Yes it is rather mechanical. Consider it a framework from which to build experience and a feel for the aircraft. I am now at the stage where I can feel where the wheels are once in the flare and I know that when I get that sinking feeling at 50 - 30 feet I am going to leave the thrust on a little longer during the flare, and when I get a sudden gust of wind and I'm suddenly Vref+15 I can bring the thrust to idle much earlier than usual. But when the visual cues are limited, or I'm landing on a 30 metre wide runway, I can assure you that seeing the reference point passing under the nose and beginning the flare before it actually feels like time to flare has saved me from a harsh landing on numerous occasions!
019360 I know what you mean too! You can't beat looking at the windsock! and having a feel for crosswind landings and being able to apply just the right amount of rudder to align the fuselage with the runway while cross controlling with the right amount of aileron to keep the wings level is one of the real joys of flying.
Like many things, it can seem complex and convoluted when written on paper (or computer screen), but in practice it is oh so simple!
And just repeating the flare technique is a framework from which you can build experience and refine with time. It is also something to fall back on when you're tired and/or the visual cues are lacking.
Yes it does rely on a consistant approach path to the aiming point, but no more than any other approach.
Sometimes you do get a gust of wind or some thermal lifting at say 100 ft and suddenly find yourself aiming a little further down the runway than you would have liked, and don't have enough room left to get it back on the correct path to your original aiming point without risking an unacceptable increase in descent rate so close to the ground. In these cases I simply move the aiming point further down the runway that equates to a new 3 degree path to the runway surface (within reason of course) and move the reference point the same distance. With practice it becomes quite easy to do.
Regarding various flap setting. Yes you are correct that that will have an effect on the glareshield cuttoff angle. The change will be the same as the change in approach attitude. The actual change is usually only a couple of degrees. cot 2 degrees equates to about 20 ft in horizontal distance. 4 degrees in attitude change varies the reference distance by around 43 ft. 43/20 = 2. So a 4 degree change in approach attitude will change your flare height by only 2 feet.
Regarding seating position. In the aircraft I fly, there isn't that much room to manoeuvre. You have to sit high enough to see over the control column to the EHSI, but low enough that I my arm is not too high relative to the control wheel and my legs are comfortable on the rudder peddals.
Yes it is rather mechanical. Consider it a framework from which to build experience and a feel for the aircraft. I am now at the stage where I can feel where the wheels are once in the flare and I know that when I get that sinking feeling at 50 - 30 feet I am going to leave the thrust on a little longer during the flare, and when I get a sudden gust of wind and I'm suddenly Vref+15 I can bring the thrust to idle much earlier than usual. But when the visual cues are limited, or I'm landing on a 30 metre wide runway, I can assure you that seeing the reference point passing under the nose and beginning the flare before it actually feels like time to flare has saved me from a harsh landing on numerous occasions!
019360 I know what you mean too! You can't beat looking at the windsock! and having a feel for crosswind landings and being able to apply just the right amount of rudder to align the fuselage with the runway while cross controlling with the right amount of aileron to keep the wings level is one of the real joys of flying.
Like many things, it can seem complex and convoluted when written on paper (or computer screen), but in practice it is oh so simple!
And just repeating the flare technique is a framework from which you can build experience and refine with time. It is also something to fall back on when you're tired and/or the visual cues are lacking.
Last edited by Blip; 21st Sep 2006 at 12:18. Reason: It was initially posed as one big paragraph for some strange reason.
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I'd say there are too many numbers floating around on this. If you add working out your crosswind at limits, you are overloading yourself. My own technique, from 747 to 737, is to listen to the proximity of the radio alt calls to judge flare strength, along with taking into account 'girding ones loins', and any gasps from the copilot, and any other visual cues. It works, without too much clever calculations and focusing on one thing only. Whenever you do that, something else creeps up and sticks it to you.
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Having spent many years teaching in pistons, jets and [variable flare engine off landings in]helicopters I must say that Ive never heard of Msr Jakobsen's profound technique.
Although I cannot discard it as potentially valuable I can only add that surely he is putting mathematics into something we've always taught/done....using such terms as 'aimpoint', 'attitude', 'energy', 'reference point' and yes, over those last few inches a 'feel' gained through experience.
Its always amused me - and more so nowadays with 'fly by wire' jets (that change Flight Control Law in those last moments and often provide a nose down bias to help us 'feel' the flare more) - that when you ask the PF why that landing went wrong he/she as dozens of reasons often commencing 10nm out!
When you ask why a particular flare/landing went so gloriously well, they simply respond with a shrug and a cheeky grin....and maybe find some spurious reasoning like "I delayed taking Reverse a nano-second"?
Although I cannot discard it as potentially valuable I can only add that surely he is putting mathematics into something we've always taught/done....using such terms as 'aimpoint', 'attitude', 'energy', 'reference point' and yes, over those last few inches a 'feel' gained through experience.
Its always amused me - and more so nowadays with 'fly by wire' jets (that change Flight Control Law in those last moments and often provide a nose down bias to help us 'feel' the flare more) - that when you ask the PF why that landing went wrong he/she as dozens of reasons often commencing 10nm out!
When you ask why a particular flare/landing went so gloriously well, they simply respond with a shrug and a cheeky grin....and maybe find some spurious reasoning like "I delayed taking Reverse a nano-second"?
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Many,many years ago, a well-respected Captain that I flew with, recounted the story of how he had recently given a lecture to his local Church, about pilot selection and training. Having completed his talk, he asked if there were any questions and was promptly asked by an elderly gentleman, who praised his illuminating talk but stated that he still did not understand how a pilot knew when to flare.
"Oh, that's the easy part" was the reply,"when the cheeks of my arse smack together, I pull back on the stick"!!
Eat your heart out Capt. Jacobson!!
"Oh, that's the easy part" was the reply,"when the cheeks of my arse smack together, I pull back on the stick"!!
Eat your heart out Capt. Jacobson!!
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[quote=Blip;2864051]
It is brilliant because you are effectively determining the height above the runway to commence the flare without having to actually think about or try to estimate what the aircraft's height actually is! Instead it utilises basic triginometry ie "the branch of mathematics dealing with the relations of the sides and angles of triangles and with the relevant functions of any angles." so that you are only using horizontal distances along the runway instead. As a result, because the approach angle is 3 degress or 20:1, if you can discern a distance along the runway of 20 feet (6.1 metres) (about half the length of a single centreline marking) you can discern a flare height to within 1 ft!!!
Get it???
misd-agin - so at 120-140 kts we´re supposed to pick out a 20´ difference? Mind you we have to have this point identified 1, 2, or perhaps 3 thousand feet away when you compute the slant angle...
Now admittedly there is around 100 ft discrepancy between this distance and the first one. But if you divide 100 ft by 20, that is the actual discrepancy in terms of height. It's just 5 feet. At 750 ft/min that equates to 0.4 of a second! Split the difference if you like.
misd-agin - Only 5'? Dón´t know about you but a landing height misjudged by 5', or even 2' feet, is not one I would be proud of. And you´re sink rate at touchdown is much lower so it´s not .4 of a second. Flare typically starts around 20', or slightly higher, but takes several seconds to complete.
This theory ignores sink rates and the actual arrival weight of the arriving aircraft. Landing an airliner at light weights typically needs a later and or slower flare vs. landing one at max gross landing weight. That´s for a normal approach. Have a 'sinker' like the FO had this afternoon and your theory would have left him humbled.
It is brilliant because you are effectively determining the height above the runway to commence the flare without having to actually think about or try to estimate what the aircraft's height actually is! Instead it utilises basic triginometry ie "the branch of mathematics dealing with the relations of the sides and angles of triangles and with the relevant functions of any angles." so that you are only using horizontal distances along the runway instead. As a result, because the approach angle is 3 degress or 20:1, if you can discern a distance along the runway of 20 feet (6.1 metres) (about half the length of a single centreline marking) you can discern a flare height to within 1 ft!!!
Get it???
misd-agin - so at 120-140 kts we´re supposed to pick out a 20´ difference? Mind you we have to have this point identified 1, 2, or perhaps 3 thousand feet away when you compute the slant angle...
Now admittedly there is around 100 ft discrepancy between this distance and the first one. But if you divide 100 ft by 20, that is the actual discrepancy in terms of height. It's just 5 feet. At 750 ft/min that equates to 0.4 of a second! Split the difference if you like.
misd-agin - Only 5'? Dón´t know about you but a landing height misjudged by 5', or even 2' feet, is not one I would be proud of. And you´re sink rate at touchdown is much lower so it´s not .4 of a second. Flare typically starts around 20', or slightly higher, but takes several seconds to complete.
This theory ignores sink rates and the actual arrival weight of the arriving aircraft. Landing an airliner at light weights typically needs a later and or slower flare vs. landing one at max gross landing weight. That´s for a normal approach. Have a 'sinker' like the FO had this afternoon and your theory would have left him humbled.
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Weather is subject to change!
Put the a/c on the c/l and see what it takes to keep it there. That's your drift.
When you're at a minimum height above the ashfelt ,flare, then chop the gas.
Put the a/c on the c/l and see what it takes to keep it there. That's your drift.
When you're at a minimum height above the ashfelt ,flare, then chop the gas.
misd-agin says:
"so at 120-140 kts we´re supposed to pick out a 20´ difference? Mind you we have to have this point identified 1, 2, or perhaps 3 thousand feet away when you compute the slant angle..."
Yes at those approach speeds you're doing around 75 metres per second. But your question is like asking " I'm driving on a highway at 120 km/h and you expect me to read an off-ramp direction sign?"
Well not if you're looking out the side window just as you pass by the sign. But if you are looking out the front window and the sign is hundreds of metres in front of you and only a couple of degrees away from your aiming point, well then yes. If you recall the length and spacing of all the markings on the runway including the centreline markings, it's actually quite easy to work out where the reference point is in relation to your aiming point on the runway surface.
"Only 5'? Dón´t know about you but a landing height misjudged by 5', or even 2' feet, is not one I would be proud of. And you´re sink rate at touchdown is much lower so it´s not .4 of a second. Flare typically starts around 20', or slightly higher, but takes several seconds to complete."
It's all about when to start the flare manoeuvre, not where the flare ends up once your vertical speed has reduced to zero! (That is [from flare initiation to touchdown] the subject of the second article I read in that same publication that I found invaluable. That one was written by an ex-airforce test pilot by the way.)
"This theory ignores sink rates and the actual arrival weight of the arriving aircraft. Landing an airliner at light weights typically needs a later and or slower flare vs. landing one at max gross landing weight. That´s for a normal approach. Have a 'sinker' like the FO had this afternoon and your theory would have left him humbled."
I agree with you on the point you make regarding landing weight, undershoot shear etc. and how these will vary the rate and amount of attitude change required during the flare manoeuvre, but I still think there is much merit it keeping the flare height consistant for each aircraft type. Again I haven't included it in this thread, but the other article that talks about the actual flare manoeuvre found in the 1987 Aviation Safety Digest, looks after all of those variables.
Hello brain fade. Thanks for that.
"so at 120-140 kts we´re supposed to pick out a 20´ difference? Mind you we have to have this point identified 1, 2, or perhaps 3 thousand feet away when you compute the slant angle..."
Yes at those approach speeds you're doing around 75 metres per second. But your question is like asking " I'm driving on a highway at 120 km/h and you expect me to read an off-ramp direction sign?"
Well not if you're looking out the side window just as you pass by the sign. But if you are looking out the front window and the sign is hundreds of metres in front of you and only a couple of degrees away from your aiming point, well then yes. If you recall the length and spacing of all the markings on the runway including the centreline markings, it's actually quite easy to work out where the reference point is in relation to your aiming point on the runway surface.
"Only 5'? Dón´t know about you but a landing height misjudged by 5', or even 2' feet, is not one I would be proud of. And you´re sink rate at touchdown is much lower so it´s not .4 of a second. Flare typically starts around 20', or slightly higher, but takes several seconds to complete."
It's all about when to start the flare manoeuvre, not where the flare ends up once your vertical speed has reduced to zero! (That is [from flare initiation to touchdown] the subject of the second article I read in that same publication that I found invaluable. That one was written by an ex-airforce test pilot by the way.)
"This theory ignores sink rates and the actual arrival weight of the arriving aircraft. Landing an airliner at light weights typically needs a later and or slower flare vs. landing one at max gross landing weight. That´s for a normal approach. Have a 'sinker' like the FO had this afternoon and your theory would have left him humbled."
I agree with you on the point you make regarding landing weight, undershoot shear etc. and how these will vary the rate and amount of attitude change required during the flare manoeuvre, but I still think there is much merit it keeping the flare height consistant for each aircraft type. Again I haven't included it in this thread, but the other article that talks about the actual flare manoeuvre found in the 1987 Aviation Safety Digest, looks after all of those variables.
Hello brain fade. Thanks for that.
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Surely we should be encouraging the flare to be terminated at the correct touchdown point, in view of the runway overruns that occur with almost monotonous regularity? The Jacobson technique is rather complicated for a 'newbie' concentrating on striving for a decent landing and if a gust occurs that means changing the aiming point to further down the runway, then aren't you encouraging deep landings?
Apart from smooth weather conditions, arriving at the flare height also depends very much on the pilot maintaining the correct rate of descent for the Vref and maintaining the visual glide-slope (PAPIS/VASIS if present). Flaring the aircraft also depends on the actual runway length and surface conditions, i.e. a short,wet runway requires a firm touchdown with immediate commencement of retardation, whereas a long,dry runway can allow for some error in the last few feet of the flight.
This Jacobson technique seems more suitable to Microsoft flights - I will stick to the technique (B747) taught to me 20 years ago " at 50 feet radio, transfer your attention to the far end of the runway so that the closing rate of descent can be judged and then ease the nose up a little whilest simultaneously closing the throttles and hold that attitude". So far I have not been called to the office to explain a high 'G' arrival!
Apart from smooth weather conditions, arriving at the flare height also depends very much on the pilot maintaining the correct rate of descent for the Vref and maintaining the visual glide-slope (PAPIS/VASIS if present). Flaring the aircraft also depends on the actual runway length and surface conditions, i.e. a short,wet runway requires a firm touchdown with immediate commencement of retardation, whereas a long,dry runway can allow for some error in the last few feet of the flight.
This Jacobson technique seems more suitable to Microsoft flights - I will stick to the technique (B747) taught to me 20 years ago " at 50 feet radio, transfer your attention to the far end of the runway so that the closing rate of descent can be judged and then ease the nose up a little whilest simultaneously closing the throttles and hold that attitude". So far I have not been called to the office to explain a high 'G' arrival!
by numbers
Any discussion about Jacobsen's technique gets mired down in the number and seems to miss the main point that arises; that it gives a very accurate method of using the visual cues that are readily observable in front of the pilot, when conducting the flare commencement and rate determination. The off nominal condition for path and speed/attitude are in the first instance easy to compensate for, and in the latter case self cancelling in effects. The technique remains just that, a technique, not a policy, procedure or mandatory practice.
I have taught and demonstrated the technique on occasion where the student showed an interest in the concept, and have used it in a variety of different types from light aircraft, western and soviet era military jets, B747, B744, B767, B777, A330, and MD11.
It is a very accurate additional cue available when understood, that may be used by the pilot to assist in his perception.
I have taught and demonstrated the technique on occasion where the student showed an interest in the concept, and have used it in a variety of different types from light aircraft, western and soviet era military jets, B747, B744, B767, B777, A330, and MD11.
It is a very accurate additional cue available when understood, that may be used by the pilot to assist in his perception.
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Whereas I would not dream of doubting the beautiful mathematics of the technique, the whole thing falls apart when you question what 'flare' is.
You flare at xx feet. OK, but at what rate do you flare and how much control force is required? Throw in a few more variables such as weight and C of G position and you're back to square one.
Obviously, what Mr Jacobsen has done is to plagerize the autoland logic and programming and substitute the autopilot with a human pilot.
The software for the autoland is such that the desired result is programmed in and the autopilot adds whatever control inputs required to produce this. The computer knows, (or at least, can calculate so quickly that you wouldn't know that it didn't), what force and rate of change of elevator deflection will be required to 'flare'. We can't, and must rely on visual and tactile clues.
You flare at xx feet. OK, but at what rate do you flare and how much control force is required? Throw in a few more variables such as weight and C of G position and you're back to square one.
Obviously, what Mr Jacobsen has done is to plagerize the autoland logic and programming and substitute the autopilot with a human pilot.
The software for the autoland is such that the desired result is programmed in and the autopilot adds whatever control inputs required to produce this. The computer knows, (or at least, can calculate so quickly that you wouldn't know that it didn't), what force and rate of change of elevator deflection will be required to 'flare'. We can't, and must rely on visual and tactile clues.