View Full Version : 737 Flaps 30 or 40

11th Jul 2001, 23:06
Can someone tell me if the 737-300 is more stable on approach in turbulence, with flaps 30 or 40?


12th Jul 2001, 04:20
I find that the 737-300 is more stable with flaps 30. The aircraft is more roll sensitive with flaps 40. If you had windshear you are better of with 30.

12th Jul 2001, 04:22

In stable weather conditions a 737 is more stable on speed with flaps 40 than with flaps 30. This is due to the higher drag and thus highr thrust settings. On the -300 and 400 the difference for the Vref is only a few Kts. On the -800 and -900 however it give you a Vref which is about 7 or 8 Kts lower than flaps 30.

On a gusty day it is customary to increase the Vref by a certain amount to account for the gust. This brings you closer to the placard speed of the selected flaps. Over a certain amount of gust this margin becomes a bit narrow for comfort. That is why on a real gusty day we normally do not use flaps 40.

With greatful thanks to flaps40 (who is presently on hollyday in the americas) for the use of her lovely name.


12th Jul 2001, 07:00
Our normal landing flap is 40, but 30 is used (runway permitting) in turbulent approaches especialy in thunderstorms. Flap 30 has more excess power available for coping with sudden downdraughts than 40 and more so at MLW.

Speed controling at 40 has a wider power-envelope so its easier to maintain an IAS than 30 on final especialy at low weights.

Check the LD required flaps 40 and 30 for the same weight. Youll find quite a marked difference.

15th Jul 2001, 15:46
Perhaps also worth mentioning that the flap-ground clearance is less with flap 40, so in a blustery crosswind I prefer flap 30. I really should practice flap 40 landings more often!

S & L

15th Jul 2001, 20:12
As said by all others, flaps 30 is much better in turb. Flaps 40 is great for nice stable days and make it easier to control speed, plus you get more applause from the back!

Have fun

18th Jul 2001, 22:24
Can some one tell me the use of Flap 2 position when to use it on B737 ???? :rolleyes:

19th Jul 2001, 22:09
Flap 2 and flap 10 were added to the other flap positions on the –200Adv in 1971 as part of a series of improvements to the wing and flap sequencing. Both are intermediate approach settings since take-off’s are only ever scheduled for flap 1, 5 or 15 and 2 & 10 are not used during the retraction sequence.

Using flap 2 & 10 reduced the aerodynamic loads on the flaps at 5 & 15 (people using flaps as speedbrakes!) because they had to be flown at the next higher block speed. Unfortunately, with the introduction of the new increased flap speed schedule last year, flap 2 is now redundant. However flap 10 is still used on approach at 170kts when the weight is below 53,070kgs.

S & L

See http://www.b737.org.uk/ for more info.
The 737 Information Site (http://www.b737.org.uk)

19th Jul 2001, 22:53
Just for interest : The -200 was able to take of with Flaps 1,2,5,10,15. Get the feeling that F25 was there too, but never seen it in our perf manuals as we never had to get that radical. But have seen valid take off data for Flaps 1-15 inclusive.

21st Jul 2001, 05:47

We use 30 flaps as a norm but 40 under special conditions ie tailwind, steep approach path, short and/or wet runway low visability etc.

I was on the jumpseat of a US carrier the other day (-200 adv) that placarded the 40 deg position as " emergency use only"

It's hard tobelieve the different theories and techniques for the same aircraft :p