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!!