PFL's
Thread Starter
Joined: Feb 2001
Posts: 37
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From: Leeds, UK
PFL's
Hello All,
Been out of action for a while hence no flying - or posts. I need to get back into practice and will require some time with an FI - stalls, circuits, PFL's, etc.
During my training we did PFL's by the high-key and low-key method (as detailed in Trevor Thom's books), but one instructor during a later check-out alluded to the constant perspective method, but did not have the opportunity to elaborate. Since then I have not found anyone who knows anything about it. Since I will have to (and need to) do some PFL's I would like to try this constant-perspective method. Does anyone know how it is executed - apparently is is a technique taught by the military.
Been out of action for a while hence no flying - or posts. I need to get back into practice and will require some time with an FI - stalls, circuits, PFL's, etc.
During my training we did PFL's by the high-key and low-key method (as detailed in Trevor Thom's books), but one instructor during a later check-out alluded to the constant perspective method, but did not have the opportunity to elaborate. Since then I have not found anyone who knows anything about it. Since I will have to (and need to) do some PFL's I would like to try this constant-perspective method. Does anyone know how it is executed - apparently is is a technique taught by the military.
Moderator
Joined: Feb 2000
Aviation Qualifications: CPL
Posts: 14,480
Likes: 178
From: UK
Yes, the best write up I've seen on it was by a chap called John Stewart-Smith in Flight Safety Bulletin, about a year ago. Personally I'm a big fan of the constant aspect method and practice it regularly.
The basic principle is that you mentally establish your "runway" in a field, and pick a point about 1/3 into it. Then you fly a constant turn (even if it's more than 360°) keeping that point at the same slant angle continuously below the horizon. Flown correctly it allows you to correct for drift naturally, and in my experience gives a very accurate touchdown engine-off.
I'm not even going to try and explain it in more detail than that, it needs diagrams. Either you need to go and look up FSB, or maybe somebody here knows a website that explains it well?
G
The basic principle is that you mentally establish your "runway" in a field, and pick a point about 1/3 into it. Then you fly a constant turn (even if it's more than 360°) keeping that point at the same slant angle continuously below the horizon. Flown correctly it allows you to correct for drift naturally, and in my experience gives a very accurate touchdown engine-off.
I'm not even going to try and explain it in more detail than that, it needs diagrams. Either you need to go and look up FSB, or maybe somebody here knows a website that explains it well?
G
Joined: Nov 2000
Posts: 24
Likes: 0
From: UK
Jolly Tall
Genghis has hit the nail on the head. It is a very useful and accurate method. During training my instructor used High Key and Low key and thank the lord I didn't have to use it. I've since been introduced to the Constant angle method which has increased my confidence ten fold. I have a photocopy of an old PFA artical that explains it very well. I also have a photocopy of an extrat from a RAF training manual that goes into it in great detail. They are now on to their third or forth photocopy and getting a bit tatty but if you interested email me and Ill send you a copy.
Cheers
H
Genghis has hit the nail on the head. It is a very useful and accurate method. During training my instructor used High Key and Low key and thank the lord I didn't have to use it. I've since been introduced to the Constant angle method which has increased my confidence ten fold. I have a photocopy of an old PFA artical that explains it very well. I also have a photocopy of an extrat from a RAF training manual that goes into it in great detail. They are now on to their third or forth photocopy and getting a bit tatty but if you interested email me and Ill send you a copy.
Cheers
H
Why do it if it's not fun?
Joined: Jul 2001
Posts: 4,782
Likes: 12
From: Bournemouth
Can someone please sumarise the High Key Low Key method? I'm not sure I know it. My instructor taught me to identify a "1000' point" - roughly where you'd want to turn downwind to base. Aim to be at 1000' at that point - if you're high, make S-turns, if you're low, cut the base-final corner. It works for me - most of the time - but the more methods you have at your disposal, the better prepared you are!
FFF
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FFF
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Joined: Oct 2000
Posts: 284
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From: UK
The constant aspect approach commences at Low Key, which is typically, Downwind with the aft end of the wing tip on the Initial Aiming Point. The height at Low Key is aircraft dependant.
Having established the vertical angle between your sight line to the IAP and the ground, maintain this angle constant around the base turn regulating it with the bank angle, ie increasing bank angle as you turn into wind. If the angle steepens turn away, if it shallows turn towards. Roll out on final at about 500ft, then take flap to bring aiming point towards you.
High Key is typically Low Key + 1000ft Upwind on the opposite side of the field (Deadside). Fly a curve from High Key to Low Key then continue to IAP. In doing so you will pass through the 1000ft point.
Having established the vertical angle between your sight line to the IAP and the ground, maintain this angle constant around the base turn regulating it with the bank angle, ie increasing bank angle as you turn into wind. If the angle steepens turn away, if it shallows turn towards. Roll out on final at about 500ft, then take flap to bring aiming point towards you.
High Key is typically Low Key + 1000ft Upwind on the opposite side of the field (Deadside). Fly a curve from High Key to Low Key then continue to IAP. In doing so you will pass through the 1000ft point.
Joined: Feb 2000
Aviation Qualifications: ATPL
Posts: 17,522
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From: England
That FSB on constant angle WAS very well written - wonder is there is an online versiom...
Having taught both techniques I can atest that they have their respective pros and cons. Contant angle is easier for the average Bloggs to gethis head around initially. However the RAF type High Low key is much better for forcing sound planning for typical altitudes of say 4,000ft. With constant angle the student often finds it difficult to get the initial entry gate right and if you don't do that then the whole thing never works properly.
Having mastered both I tend now to think of HighLow key points if I am PFL'ing from 4,000ft+ and constant angle below that.
I would also say to people about PFL's - take heart, they aren't easy. Despite having practiced them for over a decade now in a hangar full of different GA types, having taught the procedure the RAF way, the PPL way and the Approved CPL way, after sitting in on thousands of PFL's and briefing the whole thing more times than I care to remember - I still cock them up from time to time.
It is also an exercise which even if you've done OK and would have walked away there is nearly ALWAYS a couple of criticisms/comments which your instructor will point out. Which makes students often feel they are only just coping with the procedure. Remember that the sole aim is to WALK AWAY from the crash site. Sod the aircraft, even a perfect PFL onto an unprepared field will result in a bent prop and collapsed nosewheel on most common trainers...
Cheers,
WWW
Having taught both techniques I can atest that they have their respective pros and cons. Contant angle is easier for the average Bloggs to gethis head around initially. However the RAF type High Low key is much better for forcing sound planning for typical altitudes of say 4,000ft. With constant angle the student often finds it difficult to get the initial entry gate right and if you don't do that then the whole thing never works properly.
Having mastered both I tend now to think of HighLow key points if I am PFL'ing from 4,000ft+ and constant angle below that.
I would also say to people about PFL's - take heart, they aren't easy. Despite having practiced them for over a decade now in a hangar full of different GA types, having taught the procedure the RAF way, the PPL way and the Approved CPL way, after sitting in on thousands of PFL's and briefing the whole thing more times than I care to remember - I still cock them up from time to time.
It is also an exercise which even if you've done OK and would have walked away there is nearly ALWAYS a couple of criticisms/comments which your instructor will point out. Which makes students often feel they are only just coping with the procedure. Remember that the sole aim is to WALK AWAY from the crash site. Sod the aircraft, even a perfect PFL onto an unprepared field will result in a bent prop and collapsed nosewheel on most common trainers...
Cheers,
WWW
"Trust Me"
Joined: Sep 2000
Posts: 424
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From: Egham, UK
At my last renewal I was taught the following by and ex RAF instructor. (Think I remember this right -it's easier to practice than write!!)
1. Trade height for speed until u hit 80kts;
2. Pick an into wind field behind the left wing;
3. Pick a point in the distance off the left wing tip and then turn and fly towards it-crosswind;RESTART CHECKS
4. When the field becomes visual behind the left wing again, repeat 3. again -downwind;MAYDAY
5. 4 again, -base;CRASH CHECKS
6. 4 again -finals; RADIO OFF.
Fun, and it works.
I think you just keep repeating it if you are too high.
DOC
1. Trade height for speed until u hit 80kts;
2. Pick an into wind field behind the left wing;
3. Pick a point in the distance off the left wing tip and then turn and fly towards it-crosswind;RESTART CHECKS
4. When the field becomes visual behind the left wing again, repeat 3. again -downwind;MAYDAY
5. 4 again, -base;CRASH CHECKS
6. 4 again -finals; RADIO OFF.
Fun, and it works.
I think you just keep repeating it if you are too high.
DOC
Joined: Jan 2002
Posts: 1,235
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From: Niort
I've used both techniques and now find 'constant aspect' the more consistent. However! It might be a big however the main reason for this is that I fly from farm strips and over the years I have tended to stop flying the airport, transport command circuit and instead fly a circuit where I could genuinely glide back to the field I have left!!(was that the underlying reason for a 'circuit'?). Anyhow this sort of practice - which would make you very unpopular at most GA fields is virtually a 'constant aspect' approach. So my PFLs are very close to the majority of my farm strip landings. And as practice makes perfect, or at least better, so my PFLs tend to be pretty reliable.
So if all the approaches you have every flown are from conventional circuits by all means try the constant aspect - but remember that all your visual clues for action are no longer appropriate. This is suspect is why the high key low key method is generally taught to PPLs - it draws from their existing experience.
Given enough practice I think constant aspect is the way forward - but it does need significant practice. Given that I get nose bleeds if I'm more than 2000 agl it means I am always close to the low key position, so half of the technique is no good to me. Constant aspect actually helps me choose the arrival location because in a short wing Piper the glide is between 7 and 9 to 1 - so if it isn't close forget it!
Cheers
So if all the approaches you have every flown are from conventional circuits by all means try the constant aspect - but remember that all your visual clues for action are no longer appropriate. This is suspect is why the high key low key method is generally taught to PPLs - it draws from their existing experience.
Given enough practice I think constant aspect is the way forward - but it does need significant practice. Given that I get nose bleeds if I'm more than 2000 agl it means I am always close to the low key position, so half of the technique is no good to me. Constant aspect actually helps me choose the arrival location because in a short wing Piper the glide is between 7 and 9 to 1 - so if it isn't close forget it!
Cheers
