snancekl
but as an engineer I find it surprising that a function/position has been provided that increases drag but not lift...unless of course its purpose is as a brake, which may be the case.
Effectively the case. On the 757, Vref F25 was only a couple of knots above that of F30 - however, it gave you much mroe drag to keep the power "up" on Final Approach, enabling better speed control / engine response.
The airlines have now seen this and are getting 777 pilots to do F25 landings, and us Airbus guys to do F3 (Flap 3 rather than Flap Full). This keeps the Final Approach power low hence saves (a little) fuel. Depending on type the Approach and speed and Landing Distance increase by a bit, but the main effect for the crew on a steep glideslope / tailwind is dififculty having anything other than idle, against an SOP requirement of "Approach Power".
It makes the selection of F25 fairly instinctive, when day in / day out you are used to seeing a lower power setting for a F25 approach than a F30... someone takes the power away, lets go for the approach that needs less power
As has been pointed out elsewhere, most airliners on a go-around call for an immediate reduction of flap setting by one or even 2 stages - yet no increase in datum speed. Again, reason is pronounced reduction in drag (increased climb performance) with little reduction in lift.
NoD