My understanding of the 'football' is that flaps 2 improved cilmb(overrun) take-off probably allows the highest weight from a 6500'-7500' rwy. However, contrary to one of the posts above, I don't believe that F25 is used for take-off on ADV, and the highest might be F15 which is also the secondary landing flap setting.
On the approach, flaps 2 can also be selected to slow down to 180 kts (non-std), provided your plane has RPR (Rudder Pressure Reducer) which reduces the hydraulic pressure available to the rudder at low altitudes and with it chances of uncomanded yaw. Although, judging by higher block speeds mentioned above, it seems that some operators may still not have RPRs installed. Generally, all flaps settings can be used on approach and they roughly allow you to slow down 10 kts (provided you have RPRs). The actual maneuvering speeds corresponding to your weight (as used on 727, 757, 767,..) are a lot lower, but the block speeds on the 737 err on the safe side as they take the highest weight and were meant to simplify things.
As for the reason for stopping at F1 and F25 on the approach, I can think of a few reasons. One is to confirm the position of the LEDs/slats. Keep in mind that all except 2 extend at F1, but at F25 you get full extension in basics and F10 in ADV. Two is to avoid large trim changes at low altitudes causing possible trim runaways, not to mention passenger discomfort. Also you spot and stop a flaps assymetry sooner, should one happen. Since regardless of a higher position selected the flaps will go through the motion anyway, why not take the time and the safe practice of confirming their position with each selection. (In fact in the old days they used to keep their hand on the handle until they got what they selected). Normal landing flap setting is F30, and F40 is only used in adverse wx, short rwys,....requiring slower app speeds. However, F40 gate is locked off permanently in stage 3 certification to comply with noise restriction on possible GAs. I guess the folks that still use F40 for landing are not stage 3 certified?
P.S. I don't think the commonality issue is a factor for having F2 position in 737, since there is no F1 in 727 and F2 is the first position. Also the practice of selecting F5 directly would be a very dangerous habit not to confirm LEDs/slats extension at F1, and very unnecessary high load on the flaps motor. Remember that we select flaps for the speed at which we want to fly, we don't use them as speed brakes to slow down. Hope this helps folks.
Last edited by wellthis; 18th Sep 2003 at 13:51.