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-   -   PFL advice (https://www.pprune.org/private-flying/627301-pfl-advice.html)

double_barrel 18th Nov 2019 07:03

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!!!

Jan Olieslagers 18th Nov 2019 07:48

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...

double_barrel 18th Nov 2019 07:59


Originally Posted by Jan Olieslagers (Post 10620900)
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.

TheOddOne 18th Nov 2019 08:01

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

MrAverage 18th Nov 2019 08:13

1 x what the odd one just said...........

MrAverage 18th Nov 2019 08:22

...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.

double_barrel 18th Nov 2019 10:18

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!

Jhieminga 18th Nov 2019 10:56

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.

Pilot DAR 18th Nov 2019 11:51


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!).

double_barrel 18th Nov 2019 12:28


Originally Posted by Pilot DAR (Post 10621037)
: "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?

Pilot DAR 18th Nov 2019 13:45

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!

BillieBob 18th Nov 2019 16:02


....was I right to not consider flaps under those circumstances?
Absolutely. The selection of flap will not increase gliding range.

GlenQuagmire 18th Nov 2019 20:22

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.

Pilot DAR 18th Nov 2019 21:18


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.

150 Driver 18th Nov 2019 21:33

I’m speechless that anyone instructing in a high wing Cessna (can’t speak for other types) suggests that extending flaps extends a glide. It isn’t what the POH says and I’m relieved to read above that everyone takes the approach that I had drummed into me-only extend flap when you know you’re 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.


vetflyer 18th Nov 2019 23:10

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


flybymike 19th Nov 2019 00:04

Retracting flaps to extend the glide certainly occurred to the crew of BA flight 38 following engine failure on approach at Heathrow.

Pilot DAR 19th Nov 2019 01:13

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!

double_barrel 19th Nov 2019 06:50

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-****, 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!

s4ex 19th Nov 2019 09:13


Originally Posted by vetflyer (Post 10621444)
...
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...

​​​​​

GlenQuagmire 19th Nov 2019 09:16


Originally Posted by Pilot DAR (Post 10621359)
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.

Just to be absolutely clear for the original poster, if you are undershooting the field on a forced landing it is no longer a forced landing it is a crash. This is a situation where you need to re-evaluate what’s happening because it is unrecoverable. I do not agree that you doggedly stick with the original decision blindly and hit the ground at high speed short of the intended aiming point. Actually, that’s the point I was making about the original exercise. Both the instructor and the original poster knew the PFL exercise was going wrong and left the decision to bin it too late. That’s the learning point of what you flew. It would have been better to make a different decision while you had more options rather than continue down and select flaps (just because that’s what you do) and put yourselves and the aircraft in a precarious situation.

By the way, the T67 flight manual makes no mention of using flap to for improved glide. It says that you use the flap to adjust the glide to achieve the required touchdown point. It recommend the same speed for clean and the first stage of flap (70kts) and the glide will definitely be degraded by the addition of flap because of the increase drag. Just to explain that a little further - the flap will mean the wing produces a bit more lift but the wing is already generating the same amount of lift as the aircraft mass so when you select the flap you will reduce the angle of attack and keep producing the same amount of total lift. You will definitely be generating a bit more drag. So the glide range will decrease. In some aircraft you may be able to reduce the rate at which the aircraft is descending because you can generate the required lift at a slightly lower speed but you will not go as far over the ground. You may stay in the air slightly longer but will not go as far.





s4ex 19th Nov 2019 10:48

To the original poster.

There are no circumstance with a conventional aircraft, where adding even little flap would allow to make the runway which was undershot in clean configuration. I might be wrong, but it seems to me that it is even mentioned in basic Principles Of Flight ground school subject. This is due to the fact that the wings for most aircraft is designed to have the best L/D ratio at the clean configuration, and that is when the aircraft will glide the farthest. Having flaps extended, improves lift, but also changes the drag, and it does not give the same maximum L/D ratio any more, thus the glide steepens. It is possible that there are some airplane designs which incorporate the improvement of L/D ratio when flaps extended, but I suspect it is very hard to land such aircraft, because it will tend to fly at the point when it should stop flying.

To assure myself, I have event taken a Stick And Rudder copy from the shelf, and it's clearly states "Flaps have a double purpose of lowering the airplane's stalling speed and of increasing its drag, thus steepening its glide. As far as glide control is concerned, only this drag effect is important. With flaps down, the airplane's glide is so exceedingly steep that there is hardly any problem of glide control;". Not all are fans of the book, but it just proves that the basic principles exist more than half of century, and I wonder why would anyone suggest otherwise, except proven in practice.

As per the whole situation. I think You had a very good opportunity to learn many things and make conclusions. Your initial feeling was correct, and the Go-Around would have been the right action (You mentioned that You'd have done it if being alone in the cockpit, or with an examiner. I don't think this decision would count as a fail - it is good judgment). The tricky part here is that You were flying with instructor, who is the PIC, and in general, You have to trust him, because he is supposed to "know better". Depending on how long You are in training and how much experience You already have there is a certain degree of psychological influence on the student's decisions because instructor is supposed to mentor/guide the student and demonstrate things. So You got in to the trap of following suggestion of Your instructor, which is the right thing on it's own. You cannot blame Yourself for this. The issue probably was that instructor chose incorrect strategy of demonstrating his point. The ideal course of actions in that situation, IMO, could have been "You call Go-Around and execute it. Instructor accepts it, but tells that the approach could have been executed. On the next circuit instructor takes the controls and demonstrates from the same aircraft position. The exercise is finalized by the 3rd circuit, where You execute it Yourself". This didn't happen, but it doesn't mean it is Your fault in this case. Maybe next time You should call for GA as soon as You feel it and not hesitate. Don't blame Yourself and don't blame anyone, instead learn from it. As Your experience grows, You will realize that instructor wasn't always correct, but it's ok, we are all humans and all make mistakes. You are lucky to realize this now. Since You have posted this situation, and there was a discussion on it, I believe You have debriefed it quite extensively, so next time You will make the right decision.

Don't feel unsettled. This is a good lesson for You, not all have the luck to experience it during the training.

Good luck on Your further training.


double_barrel 19th Nov 2019 11:45

Thanks, useful summary of the lessons. I would actually love to do some of these exercises solo, I would probably be more conservative but I think it would be valuable to know that there is no-one to bale me out if I mess it up. Is that permitted/done ? After all, if all goes well in a few weeks, I will be out there alone anyway and I don't want to be afraid to keep working on these key skills.



Originally Posted by s4ex (Post 10621787)
To the original poster.

There are no circumstance with a conventional aircraft, where adding even little flap would allow to make the runway which was undershot in clean configuration. I might be wrong, but it seems to me that it is even mentioned in basic Principles Of Flight ground school subject.

That was certainly my understanding until this incident, so I was troubled to be told to add some flap when I thought we were about to land crash short, and there was not a snowball's chance in hell of landing too long, which is why I came here for a sanity check!

kghjfg 20th Nov 2019 05:31

Best glide is with a clean aircraft at best glide speed.
as I recall “longest time in the air glide” is a different speed, but doesn’t fly as far. I can’t remember the second speed as I’m of the view “why would I need that?”.

They are illustrated by best rate of climb and best angle of climb. I couldn’t get my head round them until I imagined best angle as a balloon rising vertically, but slowly.

I’d not go near flap until I was sure of the runway.
There’s no flap involved in best rate of climb.
I think what you describe is a practise dead stick landing on a runway.

A PFL goes down to 50’ over a field somewhere and ends with the phrase “we’d have made that” or “that would have hurt”. It might start as you rejoin the circuit, but I don’t think a PFL involves orbiting while you wait.

At something like ~300’ if it’s not going to work, you need to be telling your instructor what you’d do with no engine, in the early days “crashing” is a valid statement. “I’d try for that bit of grass” or “that taxiway” or some such, (before going around) is, “let’s just bin this and go around” isn’t

My first PFL, I picked a field covered in hay bales, when challenged I said “it doesn’t matter, we’re not actually going to land there”, that took a bit of explaining by my FI, and a change in my mindset.

back to the original question, check best glide in the POH, show your instructor, be thankful for what you learnt. It is training after all.

Sir Niall Dementia 20th Nov 2019 08:26

This chap raised the flaps to help a bit https://assets.publishing.service.go...010_G-YMMM.pdf
Page 5 is the relevant part to this thread.
Only time I've done a PFL off airfield for real in a fixed wing was at the bottom when told to climb away the engine didn't respond due to a failed throttle linkage. Subsequent landing was one of my better grass ones! The Odd One put it perfectly, almost straight out of the patter manual.

SND

s4ex 20th Nov 2019 08:28


Originally Posted by kghjfg (Post 10622363)
...
as I recall “longest time in the air glide” is a different speed, but doesn’t fly as far. I can’t remember the second speed as I’m of the view “why would I need that?”.
...

A little careless attitude, IMO. Not always One needs to glide far. The crash-landing place can be just near by, but it will be useful to have as much time as possible to "Declare Emergency, Secure the engine, unlatch the doors, and make any other preparations for the crash". Being at high altitude, One wouldn't want to be descending at high RoD while attempting to restart the engine.



kghjfg 20th Nov 2019 09:27


Originally Posted by s4ex (Post 10622464)
A little careless attitude, IMO. Not always One needs to glide far. The crash-landing place can be just near by, but it will be useful to have as much time as possible to "Declare Emergency, Secure the engine, unlatch the doors, and make any other preparations for the crash". Being at high altitude, One wouldn't want to be descending at high RoD while attempting to restart the engine.

good call, I should be more aware of that as well for that reason.
(Off to check the POH.)

vetflyer 20th Nov 2019 11:16

Hi

Don't think I was suggesting use flap to extend glide.

But have reduced flap to regain our aiming point if that flap was selected prematurely

Some posters are adamant once selected no reduction . why ?

Rgds

PS Do we have to always to unthinking follow POH eg the PA34 poh describes a short field t/o that has you slower than Vmca in event of eng. failure Just a thought

GlenQuagmire 20th Nov 2019 12:04


Originally Posted by kghjfg (Post 10622503)


good call, I should be more aware of that as well for that reason.
(Off to check the POH.)

I would have a look at the difference it makes - I doubt its more than a few seconds from a normal cruising altitude. Flying the aeroplane is crucial in the event of the failure of your only powerplant. I would be far more focussed on flying the aeroplane towards a sucessful landing site than anything else. You are likely to waste those few seconds you save trying to nail the 65kts you need for minimum sink with a stage of flap than you are just concentrating on flying the plane. If you want to get maximum glide performance try to slow down enough to stop the prop windmilling (if it still is). I soared a super cub in wave in Scotland once and stopping the prop gave an extra 250 fpm climb rate so that was fairly significant. It also rules out the random cough and short lived restart that will ruin your day if it happens at 100 feet...

On the subject of Vx and Vy.. I have heard so much rubbish talked about the difference between best rate and best angle of climb. If you are ever in the situation where climbing at Vx compared to Vy means you will miss an obstacle rather than hit it just go and have a cup of tea and consider the wisdom of taking off.. Its interesting from a techincal point of view and totally pointless from the point of view of conducting a sensible flight.

Pilot DAR 20th Nov 2019 12:09


But have reduced flap to regain our aiming point if that flap was selected prematurely

Some posters are adamant once selected no reduction . why ?
a): Because nothing in the flight manual/POH says this is acceptable, b): the take away lesson is that if you could have to retract them, you should have already known not to extend them, c): I have never found that there is any power off performance benefit from retracting flaps. What you will lose settling as the flaps retract, you will not recover later with the lesser drag. You're just spending glide altitude for nothing. If you have the altitude to waste ('cause you've chosen a close field), you won't need to retract the flaps to improve the glide.


PS Do we have to always to unthinking follow POH eg the PA34 poh describes a short field t/o that has you slower than Vmca in event of eng. failure Just a thought
No need to untihink the POH, just fly the plane the way the manufacturer has stated, and the certifying authority has approved. After the accident, it's hard to tell the investigator and insurer that you thought you knew more than the aircraft manufacturer and approving authority, so decided to do it your way!

Vmca is the speed below which controlled single engined flight is not assured. You can fly the plane slower than this speed if you choose, and a short field takeoff will probably require this in some types. You just have to notice that if, during this phase of flying, you loose an engine, it may be a good decision to gently close the other throttle and force land ahead, as though it is a single engine plane, 'cause it's not going to fly like a twin on one!

There are many more layers of experienced thought, and approving authority review in flight manuals/POHs than just the thinking of the pilot that day. if you want to operate outside their recommended practices, you would be wise to have your alternate procedure approved. I have done this many of times - preparing, and having approved, a flight manual supplement, to describe the changed operation and limitations. This is a reminded to pilots to also read any FMS which is appended to the flight manual for the plane they are flying.

double_barrel 27th Nov 2019 17:21

Hi again!

I thought I might revive this thread to give feedback on the PFL I was asked to do for my GFT. Starting from 2,000' above the airfield I was asked to land without engine. I felt it went beautifully, I played it conservatively, keeping a good bit of spare altitude, progressively going to 20 degrees of flap as I approached the threshold and then 40 degrees when it was in the bag. I landed perhaps 300 feet beyond the numbers on a 5,500' runway.

During the debrief the examiner criticized me for wasting runway. He said that on a real forced landing in the bush, I will almost never have spare space so I should be demonstrating a precise touchdown as early as reasonably possible. I said that was true, but we weren't in the bush, we were landing on a 5,500' runway so I felt it was right to allow a generous margin for error. He accepted that, but said that the point of the exercise was to demonstrate that I could do it for real.

It was a very amicable discussion, he completely accepted my argument, but it was an interesting difference in understanding of the purpose of the exercise; I was playing the hand I was dealt, he was asking me to demonstrate how I would have played a different hand!

Kemble Pitts 28th Nov 2019 10:38

Interesting Double Barrel, it sounds like you flew the exercise nicely as briefed. The rub seems to be the way it was briefed.

My thinking is that if the instructor/examiner wanted you to land as close to the near hedge as possible then he should have made that clear. His argument is perfectly valid - excpet that's not what he asked you to demonstrate.

Pilot DAR 28th Nov 2019 11:58


so I felt it was right to allow a generous margin for error.
Good job DB, you're right, minimize risk with good judgement. You can help yourself in this theme next time by stating, and then aiming for, a distinct feature a little bit down the runway. The piano keys are an example. "My planned touchdown point will be the far end of the piano keys", which will what you will then be judged on, and... you'll earn a point for thinking about keeping practices appropriately safe, which still demonstrating the objective.

If the engine actually sputtered during a misjudged gliding approach, and you had been aiming at the exact hedge, you went through it for no good reason for a practice exercise.

double_barrel 28th Nov 2019 14:05


Originally Posted by Pilot DAR (Post 10628294)
.... You can help yourself in this theme next time by stating, and then aiming for, a distinct feature a little bit down the runway. The piano keys are an example. "My planned touchdown point will be the far end of the piano keys", which will what you will then be judged on, and... you'll earn a point for thinking about keeping practices appropriately safe, which still demonstrating the objective.

You are right, that would have been the perfect way to handle it. Next time!

Big Pistons Forever 30th Nov 2019 01:07

The most important but most neglected part of forced approach training IMO is the cause check. A review of the accident record shows that up to 80 % of engine failures are caused by the actions or inaction's of the pilot. Some of these are not recoverable (eg running out of gas) but in many cases power can be restored by prompt effective action of the pilot (eg switching fuel tanks). Flight training does a disservice to students because the emphasis on flying the maneuver to get a good score on the flight test diminishes the importance of training to minimize the possibility of the engine failing in the first place or if it does fail, immediately recovering engine power

The accident statistics also hint that for every full engine failure there are probably at least 2 partial engine failures. This is never taught at flight schools but the decision making for a partial engine failure is a lot harder than for a full engine failure

Finally the condition of the field is the least important think to worry about in a forced landing. If the engine fails the insurance company just bought your airplane. Your only job as a pilot is to get the airplane down without hurting anybody, the condition of the aircraft afterwards is irrelevant. Therefore field selection criteria are in order of importance: be close, have the minimum amount of obstacles on approach, and be reasonably flat.

TheOddOne 30th Nov 2019 07:01


The accident statistics also hint that for every full engine failure there are probably at least 2 partial engine failures. This is never taught at flight schools but the decision making for a partial engine failure is a lot harder than for a full engine failure
They do indeed, and in the UK, the outcome from a partial failure is usually a lot worse than the total failure.
We certainly do teach partial failure drill. The first question for the student is 'how can you tell you've a partial failure?' The answer I'm looking for is 'loss of altitude'. This generally places one in a worse position than a total failure. We teach levelling off at whgatever power is available. If it is at or above the minimum safe manoeuvring speed, then provided terrain is OK, continue to nearest suitable airfield, looking for landing ground along the way. Once secured, then look for a reason, change tank, pump on, carb ht etc. One of my favourites is the primer, it's happened to me and air leaking by an open primer can seriously affect the power output.
I generally, then turn it into a total failure.
In the classic sudden total failure training, we teach
1. Best glide
2. Pick a field, fly circuit to this field.
3. Look for failure. I like to work left to right in the PA28, as fuel is the most common cause.
4. No failure found, MAYDAY, brief pax
5. On final for the field, once any electric flap setting complete, master off, mixture ICO, fuel off, door open etc.

Historically in the UK, there have been failures caused by pax interference 'I wonder what this red knob does?' In a recent case, a pilot admitted knocking the mags off with their knee! In another case, 2 PPLs crashed downwind running out of fuel with 2 hours remaining in the other tank...

The complete course is 45 hours. You can't possibly bring the average student to a high state of competence in that time in all aspects, so we can only do our best to cover everything. The Club environment helps I think for students to mix with PPLs and get more out of chatting with other people more experienced.

TOO

MrAverage 30th Nov 2019 08:37

Having had a partial myself, as an inexperienced instructor over twenty years ago, I always put a simulated partial in any check flight, LPC or initial test, I'm now about to send a note to remind all my instructors not to forget to include training for such!

TOO
I too put it just before the "total" failure!

double_barrel 30th Nov 2019 09:56

I think I was well taught how and when to attempt a restart, although of course they always fail to restart during training! I'm not sure how that could be safely practiced except in a simulator ?

But it's true that a partial fail was not discussed during my training. This did come-up on PPRUNE while ago and forfoxake posted this with a link to this booklet which I found interesting.

LOMCEVAK 30th Nov 2019 09:57

My philosophy regarding engine failures/loss of power, total or partial, is that there are 4 potential causes: mechanical, fuel, ignition, icing. If a pilot mis-selection, inadvertent or otherwise, has been made then it typically falls under fuel or ignition. If this philosophy is taught clearly then it applies to all piston engine aircraft and only the detail of how to analyse and potentially correct the cause needs to be taught for the type being flown.

The other generic aspect to consider is with a variable pitch propeller: leave it as set/fine if a restart is to be attempted, select coarse if the engine is to remain shut down.

I am not involved in PPL level instruction so I would be interested to know if these philosophies are taught at this level and if it is considered reasonable for an ab initio student to have the capacity to to think them through.

Big Pistons Forever 30th Nov 2019 16:35

Most GA training aircraft have fixed pitched props but I have done 3 PPL’s on aircraft with vp props. For those aircraft I add prop full coarse (low RPM) as part of the engine shutdown flow.

Also in a retractable gear aircraft I teach that all forced approaches not to runways will be performed gear up.


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