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PFL advice

Old 18th Nov 2019, 08:03
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PFL advice

Doing final practice for my GFT, I have done a couple of PFLs which went beautifully, but yesterday had a really horrible one. It was entirely my fault that we were badly setup; I went too wide, my excuse is that we were fannying around overhead for ages doing 360's waiting for clearance to start. Turning to base we were obviously low, I would certainly have abandoned it then had I been alone or with an examiner (would that have been a fail ?). However, the instructor said we could make it, I was gliding a hair under 70Kn, and was distinctly doubtful as we turned final, then the instructor said 'what about flaps?', I said I don't want flaps, I don't need that drag. He said you won't make it without flaps, between us we then mucked about with the flaps, and between us ended up with >20degrees, started sinking fast, and then had to do a last second full power to overshoot otherwise we would have taken-out the approach lights. Altogether a really unsettling experience.

So, after all that, my question is, if gliding at optimum glide speed, with absolutely no spare height, I guess putting in some flap and then lifting the nose to reduce speed might have stretched it by a few yards ? But in practice would I not have been better to keep it clean and stay at best clean glide speed? It seems rather late in my training to be asking such fundamental questions!!!

Last edited by double_barrel; 18th Nov 2019 at 09:01.
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Old 18th Nov 2019, 08:48
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Wouldn't the answer vary between aeroplane types? On mine (80 HP high wing 3-axis ultralight) I would certainly avoid flaps until I felt certain the extra drag were acceptable. The one disadvantage being that abruptly going from zero flaps to full flaps might require some quick and hefty elevator action.

And by the way, I don't see why such an experience should be "unsettling". To me it would simply be an incentive to do it all over, until I get it right. Not that my PFL exercises are always very impressive...
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Old 18th Nov 2019, 08:59
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Originally Posted by Jan Olieslagers View Post
Wouldn't the answer vary between aeroplane types? On mine (80 HP high wing 3-axis ultralight) I would certainly avoid flaps until I felt certain the extra drag were acceptable. The one disadvantage being that abruptly going from zero flaps to full flaps might require some quick and hefty elevator action.

And by the way, I don't see why such an experience should be "unsettling". To me it would simply be an incentive to do it all over, until I get it right. Not that my PFL exercises are always very impressive...
Good point, I should have said this was (surprise!) in a C172M.

Why unsettling? Maybe I overstated it, but we were seconds from oblivion and I was annoyed at myself for the poor setup followed by last second confusion.
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Old 18th Nov 2019, 09:01
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The PFL that you have to demonstrate during your test should be over open countryside, as field choice and planning a circuit to the field are key. Therefore your practice for your test should simulate these conditions as far as possible. There certainly is value in a 'PFL from the overhead', we routinely do these on the way back from another training detail, but I would say you need field choice and circuit planning at this stage.
There will be a chorus here from folk saying that the best person to discuss this with is your instructor, but it seems that you've maybe lost a bit of faith in them after your experience. Time to ask for another instructor even though it might set you back a few flights.
None of us are perfect and if I feel I've given a student less than good advice, I hope I'd tell them so and discuss where I went wrong and try to make things right next time. I must confess that has happened to me and I hope the student took it in good part. We're all still learning, instructor and student. My first CFI had over 10,000 hrs instructional. When I started instructing, I asked him how long it took before he was on top of it all. He said 'I'm still learning, every flight'. And so it is...
As a general rule, flap should only be used once you are assured of touching down mid-field flapless, then use flap to bring the touch point closer to the beginning of your planned landing area. Full flap should only be used once your landing is assured and you have complete confidence you won't land short.
Retracting flap once extended is a big no-no, so only extend them once you really feel you need them.
It's better to hit the far hedge doing 20 than the near hedge doing 70!

TOO
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Old 18th Nov 2019, 09:13
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1 x what the odd one just said...........
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Old 18th Nov 2019, 09:22
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...and what you describe is an approach and landing with idle power from 2000' above a runway - which is not strictly a PFL. Your examiner may ask you for either on the test - it's his choice. At many airfields what you are doing is not possible.
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Old 18th Nov 2019, 11:18
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Interesting, obviously a terminology difference here. I thought PFL meant an actual landing on a runway as opposed to a practice approach out in the countryside but with an overshoot. I have done dozens of the latter and they usually go OK, the problem is that you never really know how it would have turned-out!
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Old 18th Nov 2019, 11:56
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I generally use the term PFL to describe a practice approach somewhere away from the airfield. For the final part of the forced landing, practiced in the circuit with idle power to touchdown, I tend to call it a glide-in landing. Obviously you can combine the two into a PFL culminating in a full stop on the runway, but the downside of this is that you don't have much room to change your mind during the exercise and will have to land on that runway, which makes it suitable for advanced PFL students only (my terminology).

TheOddOne already mentioned that you only use flaps on final approach to bring your touchdown point back to the start of the field. The best way to judge whether to use flaps is to look at your planned touchdown point while gliding at chosen speed towards it. If it is moving down on your windshield, you are going to overshoot it. Add one stage of flaps, acquire new attitude to maintain chosen speed and reasses. If it is still moving down, or too far down the field for your purposes, add another stage of flaps and adjust your attitude again. Repeat until happy, down on the ground, or you run out of stages of flaps.

Your original suggestion (add flap and raise the nose) is one I would advise against. In a C172, especially adding flaps beyond 10 degrees will have you put the nose down significantly just to maintain glide speed. Keep in mind that you need a few knots to be able to perform any kind of flare at the end. If you add flaps, the increased drag will cause a speed decrease and you will be eating into this margin of speed. Raising the nose more at this point will only do more damage to this speed margin, and it is not something that you can get back in any way. In my view, 'stretching a glide' is an impossibility.
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Old 18th Nov 2019, 12:51
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my excuse is that we were fannying around overhead for ages doing 360's waiting for clearance to start.
If you're practicing for a possible real event, practice like it's real. If your engine quits, you're not doing 360's waiting to start, you're headed down, you've picked your spot, you've started. Every other pilot will get out of your way, every controller will let you do it in your time - I know, I've forced landed into a busy airport I was only overflying, 'right place' right time, no problem. Of course, during a practice maneuver, you're not going to cut off traffic, and upset airport flow, so the whole exercise was poorly introduced by your instructor. I don't set up a practice for a student, in practice circumstances which are designed to train real decision making and technique. It teaches the wrong priorities. If it quits, get it on the surface safely, damage free if possible, everyone else will give you space if they know you're having an emergency ('makes a radio broadcast a good idea, if you can).

Don't extend any flaps until you know that you have the landing site made. If in doubt, don't extend any flap until you have the landing site made. Once you are going to land (hopefully, on the site you chose) extend all the flap, even if they're in transit as you touch, keep 'em coming, they slow you down.

As you glide, if you suspect you're a little high for your chosen spot (which I hope you are, 'till close final) use a sideslip to get rid of excess altitude. Every training airplane will sideslip very effectively (except an Ercoupe, you're not training in one of those). A sideslip allows you to modulate the approach rate without changing speed - slip, unslip. Once flaps are out, you can't effectively retract them if you judged wrong. You can, and should unslip as you near the surface. But (and I have done it) if you need to, you can touch down a 172 in a slip, while extending flaps. I'll get drawn into a discussion about slips with flaps in a 172, fine. In the mean time, the plane will do it fine.

Best (optimum) glide speed is published as a certification requirement to tell you how far you can glide, not how easy it will be to make a well judged approach from that speed. Many instructors really don;t know this, and thus don't teach it. Yes, you can, and must demonstrate a PFL at best glide speed for the plane, but that does not make it the best way to PFL, it's just what the book says. If the engine quits, look below you for a spot, not halfway to the horizon, and then spend a thousand feet of altitude wondering if you're going to make it.

Have a read of the text from John Farley's book which I posted recently. What John writes works, and I train it to my students. I can't tell you to not learn what your instructor is training you, it's in the POH, and another pilot like your instructor will examine you, and expect you to do it that way, but it's not the only way.

At the end of your actual forced landing, I would rather read that you went through the far hedge at 20 MPH 'cause you could not get it stopped, than you couldn't post, because you undershot an hit a car on the road short of your spot. For a forced landing, mis judge too fast/high, not too slow/low. If you have to have an accident, have it slowly. If you have to explain to your instructor/examiner you mis judged, may it a not so serious misjudgement!

When your engine quits, and you're committed to an actual forced landing (four times for me) you'll be really focused, and you won't be caring about what anyone thinks of what you're doing - you'll explain later!

between us we then mucked about with the flaps
Ah... no. Either you're flying, or your instructor is. If you are the pilot, another person in the cockpit (even senior to you) should ask you for concurrence, before moving things. If they (being more experienced) feel compelled to move things, they should ask to take over. Indeed (and I've done it) after taking over and fixing things, they may give it back to you to continue. If your instructor has left things go to the point where they suddenly need to fix something, without some advice to you, they missed the mark. If the instructor is beginning to think: "Gee, DB may need a little flap to make this work..." Instructor should say to you: "DB, I think this is going to take a little flap, I suggest you extend 10". If you're task saturated, you may ask for them to do that. Ultimately, extending some flap in a 172 should not task saturate you, and a helpful hint should still leave only you flying the plane.

This is a lesson in pilot briefing, both before the flight, and during. A 172 is a single pilot plane, it does not require two pilots to fly it - so two pilots shouldn't! (unless the briefing to do so is really good!).
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Old 18th Nov 2019, 13:28
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Originally Posted by Pilot DAR View Post
: "Gee, DB may need a little flap to make this work..." Instructor should say to you: "DB, I think this is going to take a little flap, I suggest you extend 10". If you're task saturated, you may ask for them to do that. Ultimately, extending some flap in a 172 should not task saturate you, and a helpful hint should still leave only you flying the plane.
Thanks PD, very useful. But, everything you and others said above suggests that there is no circumstance in which a little flap would allow me to get to a runway that I was about to undershoot. Is that a fair assessment? I don't think I was significantly task saturated, my brain was fully functional although I was reluctant to take my hand off the throttle as I was increasingly sure we were going to need it very soon!

I know it's an unfair question, but was I right to not consider flaps under those circumstances?
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Old 18th Nov 2019, 14:45
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Take your hand off the throttle if you're gliding, you're not using it any more. 'worst is it creeps open, and gives you a little power.

An argument could be made for a 100 series Cessna that between 0 and 10 flap, there could be a little benefit for stretching a glide, because you do create a little more lift, and can glide a bit more slowly. BUT, gliding more slowly will require a lot more skill and judgement to flare, with much less margin for error. You want the flap to slow you for landing, once you are assured of making the spot. Hopefully, you've judged well enough that you're comfortable committing to the landing a bit back, and can extend flap before the last minute.

Cessna specifies to glide the plane flaps up, so glide it that way. Cessna recommends the use of flaps for short field landings, so extend them as much as circumstances permit, as said, they can be in transit when you touch if needed. Bear in mind, and Cessna says, that if you really need to stop with heavy braking, the flaps should be retracted to put the most weight on the wheels. So, it could be that you're just getting the flaps extended as you touch down the main wheels, then retracting them right away, as you hold the nose light, and apply lots of braking.

Don't worry, when you have an actual emergency, it seems to go on forever, so you have lots of time!
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Old 18th Nov 2019, 17:02
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....was I right to not consider flaps under those circumstances?
Absolutely. The selection of flap will not increase gliding range.
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Old 18th Nov 2019, 21:22
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I'm astonished that there would be any circumstances where the addition of flap would allow you to glide further. I have never flown an aircraft where any additional flap will increase the gliding range (unless you have a very strong tailwind and it allows you to stay in the air slightly longer because of the reduced sink rate). I have done very little flying in cessna trainers but have over 5000 hours in a mixture of gliders, light singles and twins, light single pilot jets, and various multi crew jets. Pretty sure the best glide range is clean in everything and the addition of any flap at all will increase drag and decrease range.

Heres my advice chap - if you are at a sensible glide speed and the reference point is moving up in the windshield you are undershooting. Pick a new field as you aint making your chosen one..

nota bene.. don't turn a training event into a reality. Trust the feeling in the pit of your stomach. You knew this was going wrong a long time before you threw it away. Learn to trust that feeling because it will save your life.
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Old 18th Nov 2019, 22:18
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Pick a new field as you aint making your chosen one..
One of the many wisdoms passed to me repeatedly over the decades has been: Once you have a plan in an emergency, don't change it unless there is no choice. This goes extra for forced approaches. Aside from allowing yourself several different landing sites which are all very close to each other, you're better to make the right decision first, and stick with it. Changing your mind while gliding down certainly wastes altitude, and invites a poor outcome. If there is an adequate landing site close, it's a better choice than the perfect looking one farther along. 'Same logic as not flying past a fuel stop, 'cause you think you can make it.

While enroute, you should be constantly considering where you might force land if the engine quit in the next minute. Perhaps the site is one you just flew over, and had a decent look. The one you've flown over and seen from several angles, is certainly better known to you than the one which is still ahead. You can't judge its suitability and distance as well. If the engine quits, you're no longer trying to get further along your route, you're just trying to get down safely. Making the best decision first, and sticking with it is an important element of things not getting much worse mid emergency. If you're really unsure about the suitability of the forced approach sites in your area, fly higher, to give yourself more time to select, and glide.
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Old 18th Nov 2019, 22:33
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Iím speechless that anyone instructing in a high wing Cessna (canít speak for other types) suggests that extending flaps extends a glide. It isnít what the POH says and Iím relieved to read above that everyone takes the approach that I had drummed into me-only extend flap when you know youíre going to get to the field

Once flap is extended it should never be retracted until you have a positive rate of climb. Very nearly learned that the hard way.

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Old 19th Nov 2019, 00:10
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Flap retraction

I not flown Cessna alot nor recently
l agree don't use flap until sure of reaching field and use full flap to bring back aiming point

Clearly remember T67M PFL that 10 flap was selected at start as glided better

Also in PA 28 instructing we did retract flap 25 to 10 if miss judged it

Wanted to get to full flap as reduced the margin over stall

So why is flap retraction such a bad thing ?

Genuinely interested

Rgds

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Old 19th Nov 2019, 01:04
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Retracting flaps to extend the glide certainly occurred to the crew of BA flight 38 following engine failure on approach at Heathrow.
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Old 19th Nov 2019, 02:13
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Using a 40 flap Cessna as an example, though knowing that different type's flaps do have differing effects, the first 20 or so flap of the Cessna does more to increase lift, than to increase drag. From 20 to 40 does more to increase drag than lift. But, even to 40 flap, there is still greater lift than with zero flap, just accompanied by a whole lot of drag. If you were to be approaching with 40 flap way back ('not sure why), and needed to stretch the glide, than yes, you could retract to 20 flap, as one would for a go around. In doing so, you will reduce drag (good), though you will loose some lift (not so good), but also, you will increase the speed at which the wing would like to stall. So, if you were gliding slowly with 40 flap, and retracted to 20 or less, your stall speed would increase, and place you closer to the stall. In that case, you'd have to lower the nose to build up some speed, and increase your margin to stall, and in doing so, you'd probably loose enough altitude to waste whatever you would have recovered by the reduced drag. The pitching moment of the wing changes, and you'll spend some time and energy adjusting and retrimming.

Thus, for any but a very short landing power on, approach, I will not extend more than 20 flap in a Cessna, until a safe landing somewhere is assured. But, I do always plan to land with full flap, so I set up my approaches with that in mind. When landing a Cessna floatplane into a small piece of lake (often, you want to keep it close to shore, to avoid the big water), I'll usually have full flap applied before reaching the last row of trees coming over the water, I'll be steep and slow, so the plane drops over the trees well. Though I could glide on from there, a little burst of power makes the landing less extreme, and safer. Otherwise, I like approaches, where a gliding landing at least in decent ground up to the end of the runway would likely work. So I won't extend full flaps till I have it made. When I used to train new pilots in the ATC810 twin simulator (Navajo sort of thing, primitive by today's standards, and no visual whatever) full flaps were a deliberate trap, by design. Once full flap was extended, if an engine was failed, a successful single engined overshoot was nearly impossible - just to drill into pilots that full flap is great, once you are very confident of a landing as intended.

I'm sure that someone wiser than I can put numbers to this (Genghis?), I just know the sensations from doing it a few times! If in doubt, refer to the POH. It's going to give you the manufacturer's preferred technique. You'll never be wrong flying it that way!
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Old 19th Nov 2019, 07:50
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Thanks all, it's pretty clear that I had got myself into landing attempt that I could not safely rescue, although of course a more skilled pilot able to hold the speed with more precision and with fewer control movements might well have been able to make it. Lesson learned! If it's going to rat-shit, bin it early, as someone upthread said, there is no point in turning a practice emergency into a real one, the lesson is learned every bit as well 150' above the ground as 15 feet!
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Old 19th Nov 2019, 10:13
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Originally Posted by vetflyer View Post
...
So why is flap retraction such a bad thing ?

Genuinely interested

Rgds
Retracting flaps results in the initial sink. If the altitude is high, then the sink may be acceptable to gain more glide distance. But being low and slow, the sink will remove any advantage of smaller flap setting and reduced drag, because the height is lost initially. More over, as soon as the flaps are retracted the aircraft needs to be re-trimmed, and that puts more workload on already stressed pilot. If the A/C was already too slow, the retraction of flaps will reduce stall margin, that is not something we want when low and slow and no power available. For highly experienced pilot, messing around with flaps when gliding with engine-out, may be an advantage to make the most of the aircraft (and this may only be valid for piston engine), but for low-hour pilots, it is more safe to follow the rule of no retraction, once extended. This is also a discipline...

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