Reducing flaps on short finals

[Flyingmac]

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.

[N-Jacko]

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 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.

[fireflybob]

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.

[skyhighfallguy]

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.

[N-Jacko]

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.

[IFMU]

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.

[9 lives]

Catch a 500 fpm downdraft out of nowhere on short final

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.

adding trim reduces the effectiveness of the elevator (by the area of the tab)

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.

[skyhighfallguy]

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.

[fujii]

Short FINAL, not short finals.

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

[9 lives]

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

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

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!

[wiggy]

Minor point of order from a lurker:

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

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.

[JEM60]

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.,

[Cusco]

And using the BA 777 at heathrow as an example is pretty lame.

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

[Flyingmac]

adding trim reduces the effectiveness of the elevator (by the area of the tab)

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.

Yes it does.

[Zonkor]

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).

[Genghis the Engineer]

Originally Posted by Cusco

Step Turn wrote


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

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

G

[Cusco]

@GTE who wrote

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

G

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:

Actions of the Commander

The Commander, on realising that he was unable to obtain any additional thrust from the engines, attempted to reduce drag of the aircraft by reducing the flap setting. However, the aircraft was now so close to the ground that there was little time for the beneficial effects of this action to take effect.

The action in reducing the flap setting was prompt and resulted in a reduction of the aerodynamic drag, with minimal effect on the aircraft stall speed: it moved the point of initial ground contact about 50m towards the runway threshold. Had the flaps remained at FLAP 30, the touchdown would have been just before the ILS antenna, but still within the airfield boundary. The effects of contact with the ILS antenna are unknown but such contact would probably have led to more substantial structural damage to the aircraft.

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

[skyhighfallguy]

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.

[Cusco]

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

[wiggy]

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.....