737 T/O flap settings

[eng1170]

Just a quick one - whats normal flap setting for T/O, had discussion with several eng's in hangar and reckon either 5 units or 10 units

Cheers ;)

[4Screwaircrew]

1, 5, or 15 (737-300) we are starting to use 5 as the norm the others as performance dictates.

[TopBunk]

fwiw, when I flew them a few years ago for BA, we used:

-200: Flap 1 for best (least:) ) noise, but 2,5,10,15,and 25 were listed as available [never used 25 though].

-300/-400: Flap 5 as default (to reduce risk of tailscrape) with 15 as an option on shorter runways.

[4Screwaircrew]

Boeing Flight Crew Training Manual lists 1, 5, 15, for 300/500 and 5, 15 for the 400.
Flaps 1 (-300) and flaps 5 (-400) take offs have least clearance.

QRH lists speeds for 1, 5, 15 only (-300) I seem to remember from ground school that for this model 2 has no practical purpose.

[BOAC]

Flap 5 as default (to reduce risk of tailscrape)

:confused:

[eng1170]

Thanks for your replies folk's, I must admit I expected plenty of 5 or 10 units as a rule of thumb, but up to 25 units!! I work on 737-400's and when we do all the flight control function tests, obviously we do flap checks and 25 units is hell of alot of flap! 15 units is hell of a lot of flap, but 25!! Surely (sorry I know - "don't call me surely!") it gets to a point where drag must be greater than lift initially, and although you say you use up to 25 units on short runways doesn't this much flap create a longer t/o run. I can see the advantage up to 15 units, because most of the flap movement is pretty much aft with little downward movement, thus creating bigger chord and greater camber thus more lift. 25 units however, there is a big change in the direction of flap movement in that it now becomes more downward, which to me, although creating more camber is bound to also start to increase drag.

If you were to use 25 units of flap on a take-off, at what point does the retraction start, is it much earlier than say a take-off at 10 units. I do realise that the flaps/gear are speed limited so from a speed point of view yes they will be, but would it be a case of get airborne and reach for the flap lever straight away and retract to a more normal flap setting for climb out.

I know this may sound trivial and maybe slighty stupid but I really an surprised to find that up to 25 units can be used. iwould be really interested to hear from any 737 crews and how they operate. Whats BA's SOP regarding short(er) runway op's in the 737?

Many thanks in advance - a real eye-opener!!

[BOAC]

Eng - on the 3/4/500 737 BA use (what I believe to be the 'norm') ie 5 and 15. I think I can remember a 25 option on the 200 series?

The whole issue is complicated by terrain around the airfield as well as tailscrape risk and runway length (bet you wish you hadn't asked :D )

The shortest take-off run (and therefore Runway limited TOW) will generally be with the highest flap setting (up to the point where little extra lift is derived - 25 I guess on the 737?)

Flap retraction will begin at 'acceleration altitude' (generally 1500' aal in BA 737 world) and starts at or above V2+15 for both flap settings, having climbed at a suitable speed (probably around ?V2+20? ish - well below limiting speed for that setting). The CLIMB gradient at F25 is less than that at F15 due to the extra drag. Therefore terrain may be a problem in the climb-out path. Thus the gain in max T/Off wt at F25 MIGHT not be significant, as MTOW will have to be reduced to allow terrain clearance as above. IE You might be able to get airborne with 2 tonnes extra at XXX in the valley with F25 but you would smack into the big hills 4 miles off the end of the runway as you flew a shallow, accelerating clean-up!

Told you it ain't easy!

[eng1170]

This is good stuff, I am following you so far. Interesting to hear how all these bits do what they do in normal op's, usually I'm just concerned with when I move the lever in the hangar does it do what it should, in the right direction, in the appropriate time and with nothing else interferring. Thanks for the info - I'll need to be asking you guy's some more questions!!