Reducing flaps on short finals

[Radix]

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[9 lives]

But let's have a sense of proportion here, reducing flap from 30 to 20 above 400' in a C172 is safe, and it worked out nicely.

"Safe" is in proportion too. It is less safe to retract flaps on final, than it is to leave them as set. Though I agree that change in those conditions should not create an unsafe situation, it is taking the plane towards an unsafe condition, where leaving the flaps along would not. It is poor form to get used to doing things on final approach which destabilize the approach, or tend to undo a landing configuration.

The fact that it might have worked out nicely is not justification for doing it. There are a lot of things which can be done in planes, and will work out nicely if done under certain conditions, which still should not be done.

Piloting is very well established now. Aside from new systems, there is not much new about piloting planes. If there is, there will be a procedure and training for doing it. I have never heard of a procedure for retracting flaps during a continued approach to landing. I have heard of maintained a stabilized approach.

[oggers]

Step Turn:

The fact that it might have worked out nicely is not justification for doing it.

The justification for doing it was that having got down to the desired glidepath he wanted to retract a notch of flap rather than carry the extra drag he no longer needed.

There are a lot of things which can be done in planes, and will work out nicely if done under certain conditions, which still should not be done.

Yeah but I, amongst others, do not agree with you that reducing flap from 30 to 20 at 450' in a cessna is one of them per se.

Though I agree that change in those conditions should not create an unsafe situation, it is taking the plane towards an unsafe condition

The condition he was taking the plane towards was 450', flaps 20, on the desired glidepath.

It is poor form to get used to doing things on final approach which destabilize the approach, or tend to undo a landing configuration.

It is entirely feasible that the pilot in question possesses the modest amount of grey matter required to understand that what worked at 450' in a C172 might not be so clever at 100', or perhaps approaching the middle marker in a 777.

[9 lives]

Okay, opening my mind...

Can anyone present any authoritative training document, standard, or aircraft normal procedure, which describes retracting flaps for a continued approach in a powered GA plane?

Test pilots and flight standards people develop and approve operating techniques for aircraft. Is anyone aware this has been done for this technique?

Is it trained anywhere in formal flight training?

Are there stated limitations or guidance as to when to do it and when not?

[darkroomsource]

It's like standing on the top rung of a step ladder.
You can do it, and as long as you're careful, you'll be OK.
But there have been a few people who've not done so well by it, so the manufacturer puts a warning on that says "don't do this".

If the manufacturer puts a warning on it that says "don't do this", and you chose to do it, then you're the one responsible if something goes wrong.

It seems to me that most small plane manuals I've read say "don't retract flaps on final".

Interestingly though, when just a couple feet above the ground, I was taught to "dump" the flaps in order to lose lift and land much shorter in certain cases (tailwheel, very short field landing). But I was being trained for "bush" flying, and I wouldn't recommend it on planes with "normal" landing gear (by that I mean used to normal stresses).

[Sillert,V.I.]

Originally Posted by Step Turn

Is it trained anywhere in formal flight training?

I was taught this during basic PPL training (in a PA-38) as a way of achieving a specific touchdown point from a glide approach.

[Flyingmac]

I've just read the first post. It says the guy was short final at 4/500ft.
I'd need full flap and some slip to get it down from that. Or a stonking headwind. Spoof?

[9 lives]

I was taught this during basic PPL training (in a PA-38) as a way of achieving a specific touchdown point from a glide approach.

Hmm, I wonder if that is a part of the approved training syllabus - I've never heard of it. Certainly the Piper Flight Manual would make no mention of it - so yes, it would be top rung of the ladder type stuff. So, yes, the pilot would become responsible for the burst tire, or hard landing if it did not go well.

That said, on a PA-38, you'd be more safe, 'cause changing flap selection is kind of like holding your hand out the window on those!

If I were type training a pilot, retracting the flaps as described would be a fail, the same as if I were type training him on a ladder, standing on the top rung would be a fail. Perhaps others would be more liberal....

[Kommandogerat]

Been lurking for a while and actually have some thing useful to contribute in this case
Have done the this (reduce flaps) few times now where i'm being taught...
And it has been VERY helpful in terms of practicing how to adjust the glide path in different conditions - where i'm learning it seems like the one constant is that the conditions are substantially different EVERY bloody time

The weekend before last, the Wx was fairly rough 10-15kt S-SE blowing, we were doing some circuits in the Sportstar - Downwind at 1000ft AGL and the instructor pulled the engine - OK no worries i think we complete the circuit normally if we play our cards right.
Established best glide, tightened up the circuit abit and turned final looking fairly good but got the flaps on abit too early considering the fairly strong headwind, at about 350ft suggested bleading the flaps off which i did SLOWLY and we cleared the trees over the fence and managed a slightly faster flapless landing without having to add power.

Weekend just gone the Wx was absolutely terrible, rip roaring 20-25kt SE blowing, w/sock fully extended - Been looking to get in some solo time but the conditions haven't really been favorable, but the instructor said it would be "Good Practice" for me in any case (haha)!!
On the ground before even starting the A/C, the airspeed indicator needle was being pushed off the stop by the wind gusts and i was thinking this will be fun.

In the circuit doing about 110kt D/wind we were motoring along very quickly indeed but turning final, it felt as if someone had suddenly attached a boat anchor to the tail as we were doing about 60kt IAS but the GPS was showing only barely 20kt ground speed.
If a normal approach profile is like descending down a comfortable flight of stairs, this approach was like going down a ladder forwards whilst staring down at the ground almost vertically. With only idle power on we got 2 stage of flaps (30deg), on then 3 stages (40deg) and we were coming down at about 1000fpm and Looking OK but as we got abit lower the wind intensity was reducing and the instructor suggested going back to the 2nd stage flaps and carrying abit more speed to the runway to ensure we were less vulnerable to changes in the wind, which was now coming from about 20deg to the left (X-wind) to make life even more interesting.
Despite the changes going on i did manage to hold the IAS reasonably constant the whole way down, even if the angle was crazy and so the approach felt stable which earned me a compliment from the instructor.

Fortunately the Adelaide weather forecast is looking good for this weekend so maybe i'll be able able to build some more solo time, but with those experiences under my belt perhaps i'll be slightly better prepared for what might come my way...

[Pace]

K

I don't know who your instructor is but to preach the use of reduction of flaps to control drag under normal operations is a very risk potential practice.

Flaps create lift and drag and there are times when drag is your enemy as well as times when you need it.

Aircraft specific on many types full flap creates more drag than lift and IMO should only be used when assured of a landing and in many cases not used at all.
Only on the very shortest runways/landing strips would I ever take full flap in a Seneca Five.

so to even contemplate removing flap or juggling them up and down like a speed brake is a risky method to use as there is always room for error especially at points of high workload.

To be in a position of having to eliminate that drag means you have got it wrong and its that which needs to be addressed not the use of flaps for drag control in that manner.

There are extreme occasions when removing that drag could save your life and you should be aware of that drag and that option but again its indicative of getting it wrong and should only be used in extreme situations usually engine out. But again why would you take full flap engine out until you are assured of landing from maybe 100 feet agl and when the profile is right to do so?

Pace

[tecman]

Pace, in general I agree with you. That said, in practicing a forced landing, particularly one made under highly variable conditions, I have no problem with an instructor demonstrating what's possible if one's initial asessment of the conditions is imperfect. And it goes without saying that I'd do whatever it took to make a safe landing in a real forced landing case, regardless of offending any purist sensibilities. As I pointed out in another thread, early Cessna manuals (for example) had nothing at all to say about forced landings, so relying solely on a POH reference for all circumstances leads to absurd inflexibility.

I do find K's description of LSA circuit ops odd, though. My own Sunday puddle-jumper these days is effectively an LSA and, in my location, winds are often strong and variable. With these little aircraft it's true that you don't want too much flap over the fence: the stall speeds with full flap are so low you welcome a tiny bit of extra speed to help controllability and reduced flaps to minimize buffeting. (This, mark you, from someone who makes a point of full or near-full flap landings in most GA SEPs except under extreme conditions).

Having said that, the principle is no different to other aircraft: since you know the strong winds will almost guarantee you'll have to cope with quite a bit of wind-shear (speed, direction or both), leave the flaps at a modest setting until you know how things are going to work out. Many LSAs are quite slippery and do require good speed control from late downwind onwards. In my case, I know I'll get a workable descent profile if I'm established on early base at 60kt with 15deg flap. The profile will be up and down a bit but controllable with attitude and power. If it's a bad day on Rottnest Is (for example), I'm more than happy to cross the fence at about 55 kt and land with the initial flap setting.

One aspect which is worth noting is that the flaps in the Sportstar and my P2002JF are relatively modest in effect, compared with the classic barn-door Cessna flaps. I would certainly be making that point to an LSA sudent: as in many other areas, knowledge of type-specific behaviour is essential.

[Pace]

Tecman

I am not at all against Pilots being made aware of any variable sources of drag and in extreme situations i.e. a forced landing being of the mindset to quickly eliminate that drag if needs be.

I am questioning why pilots would take that final application of mostly drag until they really need to and are assured that they will reach their selected landing point?

Too many times under normal circumstances we see pilots dragging in with full flap from way out when full flap IMO should only be taken when assured of a landing and the correct profile for that landing.

Addendum engine out you are limited in still air to the potential energy in the airframe and the various sources of drag more important in that situation that the drag is only added when required as part of your energy management otherwise you are using more of that potential energy to combat needless or ill advised drag

Pace

[darkroomsource]

Yes.
I think we're missing the point here.
If you are in a landing configuration and decide that you need to reduce flaps, then you have done something wrong, and should not be where you are.
The best plan is probably to go-around and get it right, rather than attempt to fix something that's gone wrong.

Flaps do 2 things:
1) enable the plane to fly slower
2) increase drag drastically

the first should be used during certain phases of flight (takeoff in some aeroplanes, approach and landing in most)

the second should only be used when you're "there" on final, as in short-short-final

there are exceptions, of course, but that's what you should be trained for, and what should be "normal" on most light aeroplanes

[tecman]

I think we're in violent agreement about what's usual. The question was raised of when flap modulation on final might be a justifiable or documented operation. Well, one such operation involves the demonstration of what's possible in unusual circumstances. And, as a previous poster noted, we don't actually know if there was an element of that in the operation described by the OP. (Maybe he should pick up the phone and ask, then put us all out of our misery!).

[Kommandogerat]

Fair comments mostly...

I don't know who your instructor is but to preach the use of reduction of flaps to control drag under normal operations is a very risk potential practice

The situations i described definitely weren't the norm and no-ones been preaching/teaching that as the standard circuit.
Pretty much every other circuit has involved which is using power and attitude to adjust the glide path in the time honored way.

To be in a position of having to eliminate that drag means you have got it wrong and its that which needs to be addressed not the use of flaps for drag control in that manner.

Yeah, point taken - next time i'm doing a glide approach i'll hopefully judge the wind abit better and not jump the gun with the flaps.

It's the same deal with a slip on final approach, we practiced that the other week too, when we needed to lose some height, of course i know it's not a stabilized approach if you have to pull those kind of tricks.

BUT on the other hand if the engine really were to fail, the experience of having practiced these things previously, means that i'd hopefully have half a chance of pulling it off when required

The Sportstar LSA has split flaps and i'm aware that they are quite different to your average GA A/C:
1 notch is 15 deg, gives lift and abit more drag lowers the stall speed
2 notch is 30 deg, gives abit more lift again but with alot more drag.
3 notch is 40 deg, not much more lift but heaps more drag.

60kt is the "normal" approach speed with 2 stages of flap on final.

It has to said also, that there is fairly big change to the trim with and without flaps, so applying and removing SLOWLY is important to avoid ending up in at an undesired attitude.

The other side of the coin was in February this year when it was 38deg C at 9AM in the morning after a couple of heatwave days.
We did quite a few full flap landings that day as the thermal energy coming off the ground was doing it's best to stop us from coming down, at various points the VSI was showing we were getting +200-400FPM on base-final!!

Keeps life interesting through...

[Pace]

K

Let me ask you a question? Why would you need to pull the last 3rd notch of flap at all or at minimum till your 50 to 100 feet and assured of landing ?

The only time I can think of is if you are high, need the drag to fly a steep profile onto the runway landing spot.

Pace

[9 lives]

Well, one such operation involves the demonstration of what's possible in unusual circumstances.

And not picking on Tecman, but there are a lot of unusual circumstances which one could dream up, and then a very non standard action to tinker with to try to make it better. Ultimately, you'll come back around to simply applying yourself to fly a good approach and landing. That good approach will include thinking far enough ahead of the plane that you're not extending so much flap so far back that it could create a problem for you down final later.

I have seen pilots with "great new ideas" about how to fly over the decades. Other than incorporating new technology (which flaps are not), I have found that the tried and true methods work best.

There is a veiled suggesting that there is a possible need to modulate flaps down final in some cases. I disagree. Using my own experience as a measure, I have landed more than 75 type of planes more than 30,000 times in 40 years, and I have never thought to reduce the flap setting on a continued approach. Further to that, fewer than 1% of those landings would have been conducted with a flap extension of less than full as I "crossed the fence". From that experience, I just cannot figure out why someone would want to start inventing needless procedures to compensate for poor technique they applied earlier in the approach - just fly the approach right in the first place!

[oggers]

Step

Okay, opening my mind...

Can anyone present any authoritative training document, standard, or aircraft normal procedure, which describes retracting flaps for a continued approach in a powered GA plane?

Test pilots and flight standards people develop and approve operating techniques for aircraft. Is anyone aware this has been done for this technique?

Is it trained anywhere in formal flight training?

Are there stated limitations or guidance as to when to do it and when not?

But you are not opening your mind, you are closing it off to any answer that has not already been provided by authority. So let's turn the question around and ask where is it forbidden for flaps to be raised from 30 to 20 above 400' in a C172? Nowhere. And yet there are plenty of references to not reducing flap on 'final'. So where do you draw the line? As long as you are legal and flying within the limits of the aircraft you decide for yourself; that is why it is called a licence and why you have the discretion to do things that some other pilots would consider unwise:

As the carb heat begins to have an effect, consider flying at a reduced power setting (and leaning more if need be), as less volume of air going through the carb at the lower power setting needs less total heat to warm it and melt ice.

...being a case in point.

[Sillert,V.I.]

Originally Posted by Pace

I don't know who your instructor is but to preach the use of reduction of flaps to control drag under normal operations is a very risk potential practice.

I don't think anyone is suggesting this is an appropriate technique for normal operations. The two applications where it might be useful are the obvious one of a forced landing without power, and in achieving a better score in a spot landing competition (no points for landing short ).

Pace, my two principal instructors were two of the most experienced chaps you could hope to learn from. They had at least 50,000 hrs between them; one had previously flown spitfires in combat. To say I was in awe of their abilities, both as pilots and as instructors, is a gross understatement.

They may not have taught everything strictly 'by the book', but I remain forever grateful for the tiny part of their combined skill and experience which I somehow managed to assimilate.

I'd suggest they had an excellent handle on the PA-38's capabilities and limitations, whether documented or otherwise; from personal experience I can say the technique works for that type. I can't believe I'd have been taught this at such an early stage if it were inherently unsafe on that aircraft. The only real danger I can see is if there were a problem with the flap operating mechanism; asymmetric flap deployment at such a low level would certainly be an additional difficulty you wouldn't want.

Another interesting memory from the past is they limited me to using one stage of flap for the hour before being sent solo (with clear instructions to deploy full flap for the big event); apparently they'd worked out that the performance two-up on half flap was similar to the performance solo with full flap, so that my first solo approach would be as similar as possible to what I'd just flown.

They certainly pushed the boundaries and I'm sure they broke a few rules, but I believe my training was the better for it.

The statistics for off-airport landings have never made for comforting reading; achieving proficiency in any skill which increases your options should you find yourself in such a situation will, IMO, only improve safety.

I'd also say it's something you need to practice, given the right a/c and situation; just having something demonstrated won't give you either the skill or the confidence to do it for yourself, especially when under pressure.

[Pace]

Step turn

I appreciate your experience and types flown and would agree with your 99% full flap to land with something like the Citation which I fly but would reverse that on something like the Seneca where it was a rare occasion to take full flap!

In the case of the Citation and jet engines drag is added to bring speeds back to VREF on what is quite a slippery airframe while holding a fairly constant thrust setting.

so there has to be an element of type specific but the principal of a stabilised approach hold across the spectrum

Pace