Turbulent Approach Less Flaps
 

Dear all,

I know that people suggest that you reduce Flaps one step when flying an approach with severe crosswind or turbulent air.

I did it my self cause I copied the procedure. Now I do question it and would like to collect different aspects and point of views and would like to understand the aerodynamic reason.

Can anybody help a little?

Thanks
Frank

- less drag
- better L/D ratio

Aircraft will respond quicker if losing airspeed.

Turbulent Approach Less Flaps
 

I'd imagine the bigger surface area given by flaps means you are more susceptible to catching more of the turbulent air. I'm trying to recall something about turb. Conditions giving more rise to stalling. With the landing configuration and less flap your decreasing your chances of both of the above.

More importantly...

Less likely to get a flap exceedance i.e. the lower flap setting usually comes with a higher limit speed i.e. gusts and large variations in IAS won't result in the flap load relief system operating or an exceedance requiring some paperwork or, worse, engineering inspection.

Was always my take on it...

Ok, Thanks!
Some interesting points.

I see the point with the increased drag. In this case of full flaps you are more a "leaf" in the wind than with less flaps, is that what you mean?

And I see the speed limit point. But here is the next question:
Lets say you have Vref 130 Wind 30 gusting 45 (as per handbook you make additional half wind plus full gust up to a max of 20kts), meaning 130+15+15 = (130+15+the remaining 5 due to max 20) = 150kts.

Will you still add the the increment of, lets say, 8kts for lower flap selection and make it to a total of 158kts?

Best
Frank

Hi Chally604,

Not sure what the 8kts is for?

In my aircraft flap 30 limit speed is 162 knots.

At heavier, but sometimes even normal, weights our Vapp (Vref for flaps 30 plus half the stead headwind plus the full gust) will be uncomfortable close to this. In these cases we might use flaps 25 for landing as the limit speed is much higher. If we did this we'd use a Vapp of Vref for flaps 25 plus half the steady headwind component plus the gust.

Boeing say bleed of the steady headwind addition at some point before landing (i.e. between the threshold and the flare) but keep the gust addition.

Any help?

Coming closer ;-)

The 8 knots are stated in the QRH as a supplement for a flap selection less than full flaps.

Actually it is 7kts for flaps 30 instead of 45 and 14kts for flaps 20 instead of 45.
This is stated in the QRH for non normal operation like single engine (F20) or stuck Flaps etc...

Now I wonder if if you would basicaly say:

Ok, Flaps 30 instead of 45 gives me an additional 7ktd as per QRH + the 20 addition due wind from the example above... Or you say:

Well I have an additional 20 anyhow and I dont care about the 7 from the QRH.

But as those 7kt are related to performace and the 20 are related to weather, I guess you are better of to add both to a maximum of 27 what you do for example in this situation as well:

Singe engine - Flaps 20 - Vref plus 14.
In case you have 30 gusting 45 you would take:
Vref 130 + 15 (half steady wind) + 5 (15kts gust but as to max 20kts its only 5 knots remaining) + !!14!! (for the flaps 20 situation) =130+20+14=164

On the aircraft I fly, the 'G' limit is less with more flaps, that may be a consideration also, it is a 20t turboprop

R. 1975

don't change anything
 

sure, I heard the idea many,many years ago that you use less flaps in certain situations...

with the exception of certain engine out situations in certain planes, and flap malfunctions...


I would not change the flap setting at all. I would use the maximum flap setting authorized by the manufacturer/FAA all the time.

Why?

So, there you go...flying for years using full flaps for landing and now , for the first time in years you use less flaps...you're doing something not routine...and you are more likely to screw it up.

you are more likely to hit the nosewheel first
you might use more runway than you have available
you might be less spooled up (in a jet) and be less able to correct with power.

you will have less of a chance to see the runway off an ILS


the idea that you will have more G loading protection is sort of odd, but it is very unlikely that you will encounter turbulence that will exceed your g limits. (in 37 years of flying, I have had two turbulence events that might be called severe...never seen extreme and much of my flying has been near the highest peaks in the 48 contiguous states.

so...why not just do what you are doing all the time...certainly add the wind/gust corrections to VREF

be on your toes ( literally too)
learn how to use assymetric thrust a bit on multi's

but every landing you ever did with full flaps is that much more experience when you really need it...otherwise you might as well do partial flap landings all the time (you'll be sorry)

Chally

On jets it is quite common to use less than maximum flap for landing, for a variety of reasons, not least of which is it saves (a small amount of) fuel, but also because of the risk of overstressing the flaps in gusty winds.

We always fly the appropriate Vref for the flap setting used, then add the wind additions to that. On a 737 the FMC gives a Vref for flaps 40, 30 and 15, and we use the relevant one as a baseline, with the appropriate wind increment on top.

No idea what the Scarebus does.

It seems to me that with lesser flap, you are in a higher nose up attitude requiring less flare and less likely to hit nosewheel first.

I started using F25 instead of F30 on our B757's years ago, this is allowed in our procedures and was suggested to me one gusty night while being given a line check.


I was so impressed at how much easier it was to handle in these conditions with this reduced flap setting that I use it as a matter of course, runway length allowing.

Chally604,

In addition to controllability issues, by using less flap you will have a higher approach speed which will have the effect of reducing the size of the crab angle for your crosswind approach. Not usually a huge factor in planning your approach but if you're working to limits, as Tesco says, every little helps.

SSR,

I assume you wrote this because you thought that by going faster you'd have a lower body angle. However, assuming you are flying at the correct speed for your flap setting, you will have a lower body angle with greater flap settings and I would have thought that would increase (very slightly) the chance of doinking the nosewheel first, as opposed to less flap.

it's rather simple. Higher energy means better coping with the disturbance, better controllability and less crab angle. :ok:

no...because as you float along, using your ''normal'' flare technique and not quite touching down,, you panic and push the plane on, but oops, you push too much and you land flat.

the FAA does require minimum flap for jets to reduce noise, but it is a legitimate landing flap setting not some reduced flap setting just out of your head.

if you have never used assymetric thrust, you don't know all the tools you have available.

it seems to me that boeing would publish different crosswind limits for different flap settings if it really made a difference...

my comment is about departing from routine...if you are in the habbit of pulling up just a bit as the ''numbers'' vanish, or the thousand foot marker vanishes beneath you, you may float.

if you are disciplined enough to just fly it on the runway with the reduced flap setting fine...but I"ll bet someone in your company will float a bit more trying for that smooth touchdown..

and of course lord spandex masher is right and I am wrong...why? because he wears spandex and we all know how irritating spandex is

Easy question :) It's even easier to answer when you try to fly airplane. I fly gliders myself though I have CPL but no job...
When you fly in turbulent air you want bigger wing loading, smaller coefficient of lift and better controllability.
Flaps will increase coefficient of lift and wing area so it's opposite what you want. So the airplane will feel any gust and will be even more difficult to control. So that's why in gliders we land with landing flaps in normal days and +2 in windy days. Also at the beginning of the tow we use -1(yes gliders have negative flaps) so you don't hit ground with wing tip which is a foot from the ground and wingspan is almost like on 737...
Also on turbulent days I prefer to fly with water ballast so I don't get sea-sick. Water ballast increase wing loading so glider is not going up and down in the smallest updrafts.
I hope my answer explains the question :)

Woooww...

Are we all all in the same industry? :}
As I posted this, I was guessing I will get two answers:
1) Idiot why dont you know?
2) Do it this way and go back to the books...

But this turned out not to be THAT easy.
Interesting. I can follow most inputs logically but I get the feeling it is more personal attitude than airmen ship or procedure.

I guess I might continue using less flaps as I had 40 gusting almost 60 in a quiet small plane a few days ago. I used on flap setting less and I was surprised how easy to flare and to land the plane was.

the last 3 ft over the runway turn out to be quiet calm anyhow.
Was one of my best landings ;)

Best
Frank

Good to see you hold your professional pilot colleagues in such high regard :hmm: An alternative to your suggestion, that most of us mere mortals might carry out, would be to hold the attitude and allow the aircraft to settle. If it's going to land long then we go around. No need for theatrics and certainly no need for pushing forward, which we've been taught not to do from day 1 (despite some recent events in NRT :rolleyes:)

Who suggested anything of the sort? What we're talking about is going from flap 30 to flap 25 in your 757/767 or from flap 40 to flap 30 in a 737. They're 'legitimate' flap settings, not 'just out of our heads' and achieve what the OP was asking about.

Since you're so concerned that we're doing non-standard things and this is going to end in tears, please point me to the Boeing Training Manual where it discusses using asymmetric thrust in any part of operation, bar trying to stop on slippery runways. I'm willing to do so with reduced flap settings.

please remember that I said it might be harder off an ILS to see the runway...the nose is upp a bit more

and that flaps 25 on the 757...I know a guy who did that and ended up pranging the tail

so...good luck brave airman...don't float, panic and pushover too much...but don't hold off too much and prang the tail

there is wisdom in knowing how much wind affects your plane at particular airports too and if the annemometer is mounted at a non standard height...knowing how the trees, buildings etc can suddenly blank the wind is worthwhile too

pontius...colleagues in high regard...I am a realist...if it can go wrong, it will...too many ''incidents'' of less than perfect airmanship

as to assymetric thrust...if you don't have it in your bag of tricks woe to you if you are in a sioux city situation or a rudder hardover and out of options, or otherwise faced with something unusual

and using a bit of assymetric thrust, whether in the manual or not (it does say that the manual is for an experienced pilot) on a crosswind landing, allows for a reserve of controlability.

ahhhh...those across the pond...hmmmm

chally604
 

what kind of plane did you have in mind with your original post?

SSR you've gone from landing on the nose wheel to pranging the tail. Do you actually know what you're talking about?

Sioux City?! I thought we were talking about landing in turbulence and not catastrophic failures.

So how do you bleed off 15 knots (1/2 the HW component) in the few (seven seconds?) between crossing the threshold and the flare? On the other hand, the 737 FCTM does say (if landing with ice on the wings) that 10 knots should be added to the final approach speed. It further states this 10 knots should be bled off from 200 ft down - not between crossing the fence and flare. Some inconsistency by Boeing, maybe?

The Original Problem was in relation to a Challenger 604.
So believe me.. I can see the runway as long as I do not crap 90 degrees ;)
We are coming with almost negative attitude and need to do a serious flare to get the nose up for a main gear landing.

But this is not the problem.

I am more worried about the "bouncing around" in the wind. we have 20 meters and 35.000 lbs weight during landing.

So there is nothing like "energy" which will keep you going no matter what.

Out of my point of view now, it doesnt make too much sense for us for speed reasons:

Flaps 30 max 197
Flaps 45 max 189

When you add the additional 7 knots to F45 for less flap setting you end up with you won 1 single knot. 189+7=196

Guess it might be more comfortable anyways as you are further away from Stall speed and have a little more energy.

spandex...yes,I do know

I know that when you do ''different'' things you open yourself up to errors...heard all the excuses...well that's the way i do it with flaps x



and it is different, in different types.

so good luck to you spandex...have lots of fun

oh and original poster...

one way to make turbulence easier to cope with is for the PILOTS to make sure they have their seat belts on very tight, becoming ''one'' with the plane. it can reduce turbulence induced over controlling.

Airbus 319 and 320 FCOM recommend CONF 3 ( less flap ) for turbulent conditions.

Some folk would prefer to use Flap Full mind.

What you're saying there is only half true, actually. Bigger planes do indeed have lift augmentation devices that increase both the camber and the surface area of the wing, thus a higher flap setting will really give you a larger surface area and so a lower wing loading, which makes the plane more susceptible to turbulence. Vice-versa a lower than full flap setting will give you a higher wing loading which makes it somewhat more manageable in severe turbulence, also because of the small increase in speed, which gives you higher kinetic energy, a smaller crab angle and increased control authority, as already mentioned in previous posts.
On gliders you only change the camber and hence the lift coefficient, the surface and the corresponding wing loading does not change. Ideally with severe turbulence you should retain your water ballast (=higher wing loading) until you've landed, this is however discouraged if not outright forbidden in most glider's POH for structural reasons, so you just set the flaps to "full minus 1 stop" for the increased speed and aileron authority.

Ciao,

Dg800

IMO being competent at landing with any of the recommended landing flaps for your aircraft type should be extremely routine! In my bag of tricks I'd much rather have the ability and confidence of landing with any of the landing flaps than being proficient at using asymmetric thrust! What if you can't select maximum flaps for whatever reason?

Strange then that you warn us of hitting the nose wheel first if we use less flaps and on the other and regale us with a story of a guy you know who had a tail strike.

So which is it?

I agree. I recently flew with two Captains who nearly had a conniption when the computer suggested a F1 takeoff, rather than our usual F5. I'd rather take every opportunity to perform the F1 takeoff or vary F30 and F40 landings.

dry clean your spandex
 

so, I know a DC9 incident of striking the nosewheel
and a 757 incident of hitting the tail. both reduced flap settings
and of course you can't realize my point...change something and you are closer to a problem...unless you are on top of things...and of course I can see you on top spandex

Your odd vision aside how do you know that "they" had "changed" something?

Do you always use exactly the same everything?

trying for a correct landing all the time is something worthy of a pilot's attention...changing an element may, i say again, MAY lead to a problem.

Can't believe the posts here from professionals!

Use Full flaps on a jet in turbulent conditions only.

Main Reason. - faster thrust response....

You win with wind shear and when you touchdown it is easier to kill the bird.
And if you need to go around the engines are already spooled up.

The rest is a load of cods wallop.

I never felt the need to use less than normal landing flaps unless a procedure was required to preclude using normal flaps. Sometimes in a small GA aircraft it made landings easier but not in an airliner. I only had one FO change flap settings to less than normal when I pointed out a rain squall close to our landing runway and to be prepared for some possible shear on approach in a 757 so he asked for flaps 25. I gave it to him but wouldn't have if it were my leg. It got a bit sporty when he floated down the runway trying to get it on the ground.

Every pilot needs to fly so he feels comfortable using his technique as long as it is approved. 23,000 hrs with no dings makes me stick with what works for me.

Bubbers, if you were the captain it was your leg. Anyway it was his technique that lead to the float not less flap. Also I believe flap 25 is normal on a 757.

Faster thrust response hey. What difference does a few percent here or there make? Measure it, if you can!

Windshear. No config changes. So you're happy to carry extra drag when you could do without are you!? Riiiiiiiight. The aircraft can also handle higher gust loads with less flap. Besides my FCOM says use flap 30 NOT 40.

the levels of education and technical understanding seems to vary significantly among the so-called professionals, why not simply follow FCOM? :ok:

Spandex, your I am the captain attitude has shown throughout your posts. I always let the FO fly the way he wanted to. I only intervened when it was outside my comfort zone. Why couldn't you. Sometimes you learn from what your FO does differently.

I don't think you learned anything from your FO's, I did by watching. They had a different learning experience and sometimes you can learn from other pilots if you are not obsessed with yourself.

Try it sometime. You might learn something.