View Full Version : Use Of Flap 40 On The B737?

BAe 146-100
27th Nov 2004, 20:27

I was wondering how often is Flap 40 used on the Boeing 737?

What would be the reason of selecting Flap 40 instead of 30?

Thanks :)
BAe 146

27th Nov 2004, 21:21
hello ba 146-100,

flaps40 & flaps 30 are both boeing certified normal landing flap configurations. because flap40 generates more lift & a lot more drag, technically the difference is a lower vref( about 4 a 5 knots) for a flap 40 landing resulting in a shorter landing roll. the "price" to pay as nothing in this world is for free, is higher thrust settings on approach, resulting in higher fuelflows & more noise.

your question was: the choise between flap30 & flap40?

it is the captains decision & in accord with company policy:eg,
"preferential landing flaps setting is flap30".(low drag, low noise, lower fuel consumption, the company likes this last assumption)
"flaps40 may be selected for a landing distance available(lda) of 7000ft or less".
"flaps40 is mandatory for an lda of 6000ft or less( is considered a short field)".
"flaps40 is recommended for cat2/3 ( lower deck angle)".

other considerations may include landing weight & runway status, dry, wet or contaminated. it is good operating practice to discuss landing flap setting during the approach briefing, so both pilots agree. i totally agree with captain marvellous summary.hope this answers your question?

Notso Fantastic
27th Nov 2004, 21:23
One reason I was told was to give the aircraft more speed stability as at light weights and flap 30 it can be difficult to slow up and speed control is easier on final approach, especially in gusty conditions. I have to say it was not borne out in my experience- I never understood the logic of flying the aeroplane in an unusual configuration in the hardest circumstances only. In windy/sheary weather, if doing a low go around, I would not want that extra drag- I'd rather be climbing away as quickly as possible, and starting at flap 40 did not strike me as a good idea.

28th Nov 2004, 08:01
My companies policy is flaps 40 for all landings. We must engage flap 40 by 1000ft. Personally i find it easier to land and control the aircraft with a flaps 30.

Reason being: The extra lift created from flap 40 gives you a high nose up attitude and causes a baloon effect just as you flare.

Flap 40 helps on short runways but is seriously not needed. Flap 30 is fine.

28th Nov 2004, 08:34
http://www.airliners.net/open.file?id=646796&WxsIERv=Qm9laW5nIDczNy03MDU%3D&WdsYXMg=QnJhYXRoZW5z&QtODMg=TW9sZGUgLSBBcm8gKE1PTCAvIEVOTUwp&ERDLTkt=Tm9yd2F5&ktODMp=QXVndXN0IDExLCAyMDA0&BP=0&WNEb25u=S2plbGwgQXJpbGQgQmVyc%2BVz&xsIERvdWdsY=TE4tVFVN&MgTUQtODMgKE=QnJhYXRoZW5zIGJhY2t0cmFja2luZyBydW53YXkgMDcgYWZ 0ZXIgYXJyaXZpbmcgZnJvbSBPc2xv&YXMgTUQtODMgKERD=Mzk2Nw%3D%3D&NEb25uZWxs=MjAwNC0wOC0yNg%3D%3D&ODJ9dvCE=&O89Dcjdg=MjkwOTg%3D&static=yes

Believe me you want flaps 40 on this airstrip on a winter day when braking action is poor.

28th Nov 2004, 08:37
Reason being: The extra lift created from flap 40 gives you a high nose up attitude and causes a baloon effect just as you flare.

Are you sure? In the 737-200 /300 and /400's I flew the opposite was true.

The approach at F30 would be about 2.5deg Nose up vs F40 at 0 deg Nose Up - ie lower nose attitude with Flap 40 set. As for a balloon effect with Flap 40, would have to disagree there also - the greater drag causes for the aircraft to settle quicker than with Flap 30 when you close the thrust levers.

Maybe the 737NG is different?

Notso Fantastic
28th Nov 2004, 08:42
A very large British 747 Classic operator used to do standard full (30) flap landings instead of 25 flap. About 20+ years ago, flaps started falling off, and a Boeing team came over to see why only one very large British operator was so affected. They were not impressed as Boeing were designing the machine for standard flap 25 with 30 available for special circumstances, and stressing the system for that.

I believe the 737 up to -400 was designed this way, with mainly flap 30 intended to be used. It might be worth checking the Boeing manual itself to see if perhaps one of the airline management team is allowing a personal preference to override the manufacturers intention!

28th Nov 2004, 08:45
the rwy is 1640 meters long or 5400' feet.
And sometimes the braking action is reported to be towards 20 "my" (poor).
A lot of times it is a calculation whether you can land or not.
A lot of mountains around creates very unstable and rough winds.
You don't want to be without the 40 flap option.

28th Nov 2004, 14:18
For our -300s Flaps 30 was standard with F40 used for short fields but on the -800 F40 is standard to reduce landing speed. Flaps 30 is only used with very long runways or gusty wx.

30th Nov 2004, 09:41

I dont know about your airline, but our policy outlines that any runway we land on must be able to stop the plane using a FLAP 15 with MAX auto brakes available. We are not permitted to land on a 5500ft runway, even though the 737 can stop on it.

30th Nov 2004, 10:14
Why flap 40?
'Cos there isn't flap 50!

30th Nov 2004, 12:42
Bantios. How very strange? Is this an approach-climb problem as it seems a bit silly to do a flap 15 landing and have all that speed to get rid of by using max autobrake. Very expensive policy.

30th Nov 2004, 17:21
Hudson, from what I understood, Bantios was saying that if they can't operate with F15 and max auto brake into one particular aiport, they don't at all.

On the other hand, on day-by-day ops, F30 (or 40) is used instead.


Shaka Zulu
30th Nov 2004, 21:27
Flap30 is very useful in turbulent condition, it sits a lot better on the approach.
Flap40 typically gives you 3/4 kts lower speed on approach

1st Dec 2004, 09:14
Personal preference: If the aeroplane is well below 44 tonnes, then i find F40 better for speed stability and you fly the app with a more sensible N1.
I'd rather have the response/spool up from 55ish% at F40 than flying along at 45ish% N1 with F30 at a Vref of 115-120 (esp. in light -500) and the whole thing handling like a rice-pudding....

Flap travel between 40 and 30 is pretty fast anyhow...

Performance-wise (for a G/A) i'd be suprised if there was any significant difference (If there is I'd expect it to be promulgated somewhere..)

As far as gusty conditions go.....well....if you're really light you've got 40ish+kts margin before flap-load relief is required to do its thing...

Notso: point taken about what might be in the Boeing manual...will raise the issue with our TSC....get them to clarify if any doubt.

1st Dec 2004, 09:27
Bumble bee. Figures that I saw in Boeing Airliner magazine on the 737-200 indicate that the all engines rate of climb with 40 flap is 1150 fpm as against 1550 fpm with 30 flap. Hence best to use flap30 if windshear suspected.

1st Dec 2004, 09:46
HSWL , cheers... how recent was that?...i'd be interested to read it.

btw i'd certainly make a distinction between gusty/strong wind conditions and Windshear proper.....

Down...2 greens
1st Dec 2004, 20:05

See also Operations Manual Vol 1, S.P.16.15 under 'Windshear Precautions for Approach and Landing': "Use flaps 30 for landing"


2nd Dec 2004, 06:56
Thankyou for understanding what I am trying to communicate here. This policy is to safegaurd us incase of flap problems (Common on the 737). Most airliners have some sort of landing policy regarding this.