Reducing flaps on short finals
 

Hi,

About 9 months ago I was a passenger in a C172 - we were a little high on approach so the pilot, on 20 degrees flap, selected full flaps (30 degrees) on short finals. At about 400 - 500 ft coming in to land the picture of the approach appeared that we would need some more power to take us to the threshold. Instead of adding power the pilot reduced flaps to 20 degrees which flattened the approach and we landed on the keys with no extra input of power.

It was the first time I had seen this technique and wondered if this was acceptable (ie safe) and wondered what might the pitfalls be if this practice is not safe.

Thanks in advance,

Mixturerichlean.

It's a very unusual way to use the flaps.

Did he maintain a constant power setting during the approach, or was the throttle at idle?

Is he also a glider pilot? He seems to be using the flaps as a glider pilot would use airbrakes.

Perhaps he selected flaps 30, and then changed his mind for some reason unconnected with height, (Perhaps because the crosswind was stronger than he thought) and just appeared to be controlling the height with flap?

You could always ask him!

In any case, I see no danger in adjusting the flaps from 30 to 20 at 400'-500'.



MJ:ok:

mixturerichlean

I prefer not to do this though I have seen it done. One time a copilot in a turboprop plane did this and I watched with interest. I asked him why he did that?

He said, so he didn't have to touch the throttles.

And I asked him what was so hard about moving the throttles?

He said it was "COOL".

I said it was dumb and not to do it on my plane again.

I think the pilot who did this probably wasn't much of a pilot. But he was COOL. So, do you want to be COOL or a good pilot?

IF you want to be COOL, do what he did.

IF you want to be a good pilot, well, need I say more? wink wink, nod nod.

I prefer the old "power for altitude, pitch for speed" method, pulling in the flaps on short final just does not seem right to me. If it was a low time pilot I would say that if you felt the need to bring the flaps in then you're not on a stabilized approach so just power it in and bring her round again and try a little harder to get it right second time around.

Raising the flaps increases the stall speed, so if he was slow to start...

Reducing flaps on short finals
 

..........

The one thing to be said in favour of this method is that one is better prepared for a loss of engine power.
Myself was taught to land my microlight with no power at all, and slightly too high on final, then sideslip to land on the numbers (if any!) or even before.

Should I find myself too low and/or too slow on short final (iow, short on energy, as rightly pointed out above), reducing flaps would be my natural reaction. None the less one hand will always be on the throttle, during landing.

It is hard to say something real helpful without knowing a bit more about the pilot and the aircraft. If seen from training perspective and aiming for low-timers it is an absolutely NoGo - if you do so in training session or checkride your best bet is to fail.

Now the but, you can do this on a very friendly aircraft like some 172s, especially the older ones with 40 flaps - IF AND ONLY IF you know exactly your plane. DO NOT, repeat DO NOT do this on unfamiliar or tricky planes. If you are a little low or trimmed on slightly off wrong attitude, you may fall from the skies.

Yes, I have seen this - most of the times from experienced glider pilots and on power idle, but they definitely have a different education and it remains dangerous on certain conditions. Yes, I have done it, but only when absolutely sure of the situation, but never below 600ft.

So, I would conclude - it is a procedure for experienced pilots only in very certain aircraft only and in certain conditions only, and not to be tried by low-timers.

My personal feeling, never to be done when pax aboard. If you kill yourself, fine it's yours, but do not, never ever, expose passengers to unnecessary threat!

Larger aircraft have speed brakes which we usually pop if given a speed reduction by ATC or other situations where speed needs to be reduced or contained or a steep rate of descent is required.
they are noisy for PAX so instinct is to only use them if needs must.

some small aircraft have speed brakes some as a conversion some as standard. I think one of the moonies is fitted with speed brakes.

Most of the lift on flaps comes in the lower extension levels fully extended they are mostly drag so I can see the temptation to use that drag portion as speed brakes but its not really good practice

Pace

skyhighfallguy
 

Your COOL guy would have been far more COOL if he had got it right in the first place. :)

Raising the flaps on short final worked for the captain of the BA 777 whose engines flamed out due to fuel line blockage with ice at Heathrow a few years ago.

He didn't have the luxury option of adding more power and the manoeuvre got him over the perimeter fence onto the airport rather than crashing on houses.

So the trick must have some merit........

http://news.bbc.co.uk/1/hi/uk/8505163.stm

Cusco

Cusco

Its a form of drag and we are talking about energy management so I can see occasions when removing the drag part of the flap stages could be useful.

In an engine failure full flap should be taken when assured of landing but pilots do get it wrong and I could see that removing that drag could extend the glide range

I know in my Seneca Five days I rarely used full flap for landing unless the runway /strip was very short especially in a twin you want as little drag configured to land as possible in the event of an engine failure or even a go around.

Pace

I would retract some flap on final approach, if I had just applied power for a go around. Otherwise, I would not.

I would be embarrassed to have placed myself in a phase of flight in a GA plane where raising flap for a continued landing could have any plausible benefit.

I've never flown a 777, so have no qualified comment on flaps use on that aircraft.

I agree with what's been said. It's not something for an inexperienced pilot, and it's a little unusual within a GA environment.

But if you know the aircraft, if you're above Vs and if you're prepared to handle the inevitable pitch change, then you can indeed use the last stages of flaps as a form of energy (drag) control.

At the very least you're showing some courtesy to noise-sensitive neighbors. And it's good practice for an engine failure scenario.

I have myself retracted flaps on final, but for a different reason. I was on a straight-in approach in a fairly strong headwind (35 knots or so). I was fully configured for landing, with full flaps, maybe a mile away, and the runway did not get any bigger anymore. So I added some power, removed the last stage of flap, and added the flaps again when I was just before the threshold.

To me, flaps are just one of the flight controls. You need to know what they're doing, and how you can use them in different scenarios, within their operational limits. Just applying them by rote as you learned on the PPL course is good and will keep you safe, but there are other ways of doing things that are equally safe and maybe more effective.

Flaps on C172 are Fowler, and increase wing area as well as lift and drag. A go-around from a flaps 40 approach demands flaps be reduced to 20, as that last 20 - 40 is nearly all drag, the last 10 a LOT of drag. It also demands a very strong forward push on the yoke to maintain attitude until the drag-flap (40 back to 20) is retracted and the aeroplane re-trimmed. I imagine this is why Cessna limited full flap to 30 on later models - a retrograde step IMO. Just about the best feature (it an't got many!) of the 172 was that 40 degrees of Fowler flap.

Reducing from 30 to 20 will remove mostly drag, not reduce much lift, and not reduce the wing area so is a safe thing to do on final just as long as you are sure the retraction stops at flaps 20 and not beyond!

However it is poor technique and indicates poor approach planning. You shouldn't commit to flaps 30, still less flaps 40, until the point in the approach where such a setting is appropriate.

I only remember once retracting flap on final. It was in a PA38 at Alderney. I knew the threshold was near a cliff edge, and with the fairly strong wind there would be a very strong downdraft on final where the wind flowed over the cliff edge and down. But the 'clutching hand' that pulled the aeroplane seawards was far stronger than I had anticipated. The simple flaps on the Piper were retracted to first stage as full power was applied and we made the runway. I doubt we would have with full flap left extended.

SSD

I agree with what you are saying it is a bad piece of planning and why would you want 40 degrees unless landing on the shortest runway with a steep descent?
In which case take the last stage when all is looking good for a landing and not before.

Nevertheless its a big chunk of drag like an air brake and should be regarded as such pop the air break section away when you do not want that drag.

again its energy management which is not fully taught and knowing your aeroplane

Pace

It is true that the flaps are a flight control, but they are considered a secondary flight control and not the primary controls of elevator, aileron and rudder.

Perhaps your flap boy was trying to show off. But you concentrate on the fundamentals and it will pay off.

As a low hour pilot, I prefer to be well set up on late final. Maintaining correct speed for me is not a huge challenge, but requires a little effort. Are we not taught to do this for a reason? The change attitude, airspeed is significant when changing flap settings. Adding a little more throttle can fix the issue and seem less fraught with danger to me than reducing flap.

Call me simple, but I prefer the low risk approach to flying.

..........

It’s obviously something you can do but I wouldn’t recommend it as normal practice. In some types it could bite quite badly at low level, especially if you were a bit on the slow side.

It’s a useful technique if you’re undershooting with no increase in power available and still have some air underneath you. Bear in mind that the initial effect will be for the undershoot to worsen before it gets better.

The pilot in the OP seems to have decided on a land flap setting, then changed it on the way down for reasons not much connected with airmanship. Although it probably didn’t matter in this instance, it’s a sloppy way of doing things and if it became a habit, could cause problems on limiting runways. Stable approaches aren’t just a good idea for airliners...

Judging by some of the comments, you wouldn't think that 40 degrees was the recommended approach flap setting for a large chunk of the light GA fleet.:*

I couldn't disagree more strongly. We have primary flying controls for power, lift, drag, pitch, roll and yaw. There is nothing embarrassing about practising for the day when one or more of those controls is t/u or simply not up to the task. Catch a 500 fpm downdraft out of nowhere on short final to an alpine one-way like Corlier? Well, you can smack into the cliff face with old Steppy, or you can add full power, pitch forward and lose some flap while he's still looking for his flight manual.:ugh:

Some aircraft have large trim changes if you change flap settings - maybe not such a good idea when you're close to the ground on final approach.

I shudder to think that using flaps to control glidepath is really a normal thing

Certainly one can prove you can fly around the pattern with elevator trim and opening and closing the doors of the plane to make turns

BUT YOU DON'T DO THAT normally.

And what would the pilot in question do if he were flying a plane that didn't have flaps! OH NO, he couldn't possibly fly a plane that didn't have flaps.

And what if he had an electrical failure and couldn't change the flaps?

IF you want to experiment, you can do it without passengers on board.

It isn't cute, it isn't right, it isn't good flying.


And using the BA 777 at heathrow as an example is pretty lame. And didn't the captain lose his job? Hmmmm.

Yes, the trim wheel. I trim for level flight with one stage of flap on downwind (or "outbound" on a one-way) and then leave it alone. I don't have enough hands to fiddle with the trim wheel on final, while adding trim reduces the effectiveness of the elevator (by the area of the tab) and interferes with muscle memory for a constant apparent rate of closure approach.

If a Maule is trimmed level downwind with take-off flap, it's pretty well set for a go-around on airfields which offer that luxury.

Your machine may vary, and you may prefer to operate differently, so like all the other drivel on this forum, the above advice is worth what you pay for it.

My SGS 1-35C had flaps for glidepath control. I have removed flaps on approach for that glider.

Glider, pawnee, 172, arrow - most of the end of the flap travel is drag, not lift. If you go to power up and the power is not there, do you give up? Personally I have played with them all.

You can argue that needing to change flap settings, or power settings, or sideslip is a display of poor planning. It is wonderful when you plan well enough, and that the conditions are predictable enough that you don't have to do anything. Often what separates the pilots from the aircraft drivers is how they react when things don't go as planned.

Flaps are not a flight control, they are a lift and drag device. For the occasions when you encounter rapidly settling or rising air, you fly the plane through it. You manage pitch and power to maintain an acceptable approach path, or go around.

Your well planned approach should have built in allowance for variations, because your judgement has enabled you to plan well. In the case of a sudden and unforeseen change in the air movement, electric flaps will be much too slow to have any beneficial affect as a "flight control". Manual flaps are rapid enough, but the danger in accidentally going from full flap to zero flap at a slower approach speed far outweighs the benefit in changing approach path.

Happily, I have reviewed the flight manual prior to flying the aircraft, and know that no aircraft I have ever flown includes reducing flap extension during a continued approach as an emergency or normal procedure.

During certification testing, it will have been demonstrated that the most rapid selection from full to zero flap which can be made, can be flown through and recovered, but there will usually be quite a lot of altitude loss.

We aspire to a stabilized approach, which progressively configures the aircraft for landing. Retracting flaps would not conform to this. It "de-configuers" the aircraft, and introduces the risk that the landing gear might be mistakenly retracted. If a pilot I were training did this, we would have a long talk about it, and they would not do it again, if they wanted my signoff.

If you feel the need to reduce flap extension during final approach, you should go around, things are too far gone to continue a normal approach.

Not in any certified aircraft it doesn't. In some types, adverse elevator trim can be effectively used to increase elevator effectiveness, albeit with a lot of muscle needed.

let's get something straight, if you want to play around with secondary flight controls instead of primary flight controls, fine

but do it by yourself without passengers.


And you should always be in trim. Always except perhaps in the last seconds of flare.

Muscle memory is fine, but if you are on final you should be able to let go of the control wheel and the plane remain where you left it in calm air.

I'd like to see those proponents of flaps as glidepath control do it on a normal FAA checkride . IF the examiner was generous he would let you do it again. If not, he would fail you and I would have such a good laugh.

Short FINAL, not short finals.

The OP mentions 400 to 500 feet. In a normal approach, who'd consider this to be short?

"Final" Indeed! We shall do one final approach to one landing!

500 feet up on final is not so much "short" as it is in the phase of the final approach where there should be no guesswork or fiddling to be done, other than flying a stabilized, and configured approach to the landing. De-configuring the plane at that point would be rather poor airmanship!

Minor point of order from a lurker:

To cut to the chase, no.

For reasons various he decided to leave BA a while after the accident..he subsequently returned to the company with no loss of seniority. He is still a captain on the C777 for BA.

Hope that helps/clarifies the matter..back to lurking.

Yes, PB did rejoin BA, but the last I heard had decided to take voluntary redundancy after a short time. MAY be wrong. Sorry about thread drift. 172 definitely heavy push forward on a go-round on 40 flaps!!. Much re-trimming etc.,

What tosh: the 777 scenario was virtually identical to the OP:

PB in 777 realised he was sinking too fast with landing drag flaps out and with no power available retracted the flaps.

Reduced drag thereby gave him less sink, just enough to hop over the fence and avoid landing on buildings outside the airport.

The OP's scenario was of the pilot in a situation where on final he needed more power (which in this case was available to him unlike the 777) but chose not to use power and instead retracted the flaps and got in.

Both scenarios highly non-standard, virtually identical and not to be recommended, but both achieved a survivable result.


Cusco

Yes it does.

Related practice
 

A related topic is dumping flaps on touchdown, which is a quite widespread practice for short-field landings (or in microlight flying to prevent the damn thing from bouncing off again).

I've seen a very experienced pilot do it in one combined move during roundout. We came in quite steeply with full flaps and speed just above Vs0 on short final, then just above the ground he did an aggressive flare and raised flaps quickly. Elevator balanced out loss of lift nicely, making it a pleasant arrival (and the shortest landing I've ever witnessed in a spam can).

IIRC, the AAIB report on the 777 prang at LHR concluded that partially raising the flaps had no significant effect upon the outcomes.

G

@GTE who wrote
That's not what the report says:

Direct quote from the AAIB (below) shows that without the flap reduction the 777 would have crashed through the ILS antenna:

As it was, the flap reduction moved point of ground contact 50m towards the runway threshold, missing the ILS:threshold

quote from AAIB Report:

OK the pilot in his book thought he would have hit houses but his actions IMHO (and those of the AAIB) despite the lateness of the flap reduction, obtained some benefit .

I took a particular interest in this accident as at the time one of our aeroplane group members was a BA777 Captain, knew PB and I discussed it with him extensively.

Cusco

cusco

TOSH ON YOU.

the 777 thing was an emergency

the 172 change of flaps, when power was easily changeable and available was not an emergency.

Can YOU see the TOSHING difference?


how many times do BA777's practice changing flaps below 500' or 1000' with a full load of passengers. I certainly hope the answer is 0.

Oh dear:

The simple(and only) point that I am making is that, in the absence of power whether voluntary or involuntary, the dumping of flap in the OP's mate's case and Capt Burkill in the 777 had the same effect: prolonging the glide just enough - in the OPs case to land and in the 777's case to miss ploughing through the ILS gantry.

No more, no less.

I'm not commenting on the wisdom of either.

Oh and GTE's memory of the AAIB report was slightly adrift.

Chill chaps, this is PPRuNe after all.;)

Cusco

if you're going to keep bringing the 777 and "landing/drag flap" into this.

Flaps 30, 25 and Flap 20 are all valid landing flap settings on the 777, though F20 is reserved for some non-normal situations (usually but not exclusively if performance is an issue, e.g single engine landing). PB thought out of the box and swopped one valid landing flap setting for another one, albeit at very low level.....