I would guess it reduces the pitch attitude required during rotation to get airborne. Shorter rotation time to get airborne means less distance and also provides more margin for tail strike prevention at the lower lift-off speeds achieved from the higher TE flap settings.Remember, when you lower slats, you actually decrease the AoA of the wing. The AoA is the angle formed between the chord line and the relative wind / flight path. The chord line is drawn from the tip of the LE to the tip of TE. So if the tip of the LE is drooped, as in when you deploy slats, then the chord line would drop a few degrees as well.That is why if you are in un-accelerated straight and level flight and you deploy only the slats, you will need to pull the nose up to keep the aircraft from descending. Very noticeable and a common newbie mistake in aircraft that deploy only slats in the first selections of Flaps (like the 747 and the 737 flaps 1 settings.) When you call for "Flaps 1", or only for slats, you should anticipate needing to raise the nose, otherwise you will start descending. Basically, the opposite as you would expect when selecting TE flaps, when you need to decrease pitch attitude to compensate for the "ballooning" with TE flaps deployed.And keep in mind that LE slats don't increase your coefficient of lift for a given AoA. What LE slats do is to increase the critical AoA of the wing. So if your wing stalls at 15 degrees AoA, then fitting LE slats might allow you to reach 20 degrees before the wing stalls. If you want to increase your coefficient of lift for a given AoA, then you need TE flaps, of which slotted fowlers are currently the best at achieving - hence why it is the most common flap system in swept wing airliners these days. With the 737, which I suspect is the same as the 744, any position after 25 degrees adds mostly drag with little or no gain in coefficient of lift. Which I suspect is why they limit the flap setting on the SFP to 25 degrees.It is quite interesting to see the tweaks manufacturers apply to squeeze more performance from aircraft. Take the 777-300ER. Boeing has a SFP feature in the ER that locks the main gear trucks to reduce TO length. During a normal TO, the aircraft rotates on the trucks during liftoff. By locking this gear tilting mechanism, the aircraft rotates on the aft tires of the main gear (sort of the same effect as moving the main gear mounting points aft a few feet back). This provides more tail clearance for TO, which in turn allows a further reduction in Vr - hence the shorter TO distance. Quite useful when operating the aircraft at its limits, especially in high elevation airports where the big twin starts to loose a lot of performance.

Very helpful information, thank you!

One of the contributing factors of the SFP during takeoff is the ability to select flaps 15 for takeoff. On the normal NG, this would be limited to flaps 10.

Are you sure about that sir?Bert Van Bulck

SFP can use F25 for takeoff without the slats going to full extend. That's probably the big boost for T/O performance off of short runways.Classics and NGs can use up to F15 for takeoff without the SFP.

Hey Matt, I can take off with flaps 25 in the NGX with the SFP disabled.No warning and the FMC is fine with it.Can you confirm this isn't correct?Bert Van Bulck

Hey Matt, I can take off with flaps 25 in the NGX with the SFP disabled.No warning and the FMC is fine with it.Can you confirm this isn't correct?Bert Van Bulck

Well, I thought it was 25 for the SFP, but I looked through my performance handbook, and it looks like we do have tables for F25 departures out of some airports in the 800W without the SFP. I guess I'll have to look at the 900 and 900W now, as well. . .Good catch, Bert.EDIT: It looks like I have F25 takeoff numbers for all of the NGs I fly. The -400 doesn't have F25 data. So, let's say Classics can do up to F15 and NGs can do up to F25.I guess I've only ever needed F25 on the SFP-ETOPS birds.Interesting thing about my SFP planes, they don't have the extendable tail skid. Bean counters, I guess.

I think the tail skid is only on the longer models (800 and up?), not really sure.I have a buddy at Alaska, and he told me they use the F25 option to get off from some of the short Hawaiian airports when they go back to the mainland. Pretty impressive as some of those runways are pretty short and after getting off they fly for 5 hours back to the west coast. I'll have to get some more details as to where they use it and if they are weight restricted.

I think the tail skid is only on the longer models (800 and up?), not really sure.I have a buddy at Alaska, and he told me they use the F25 option to get off from some of the short Hawaiian airports when they go back to the mainland. Pretty impressive as some of those runways are pretty short and after getting off they fly for 5 hours back to the west coast. I'll have to get some more details as to where they use it and if they are weight restricted.

I think I've used it every time in Lihue. The palm trees at the end of RWY3 come up real quickly with only 6500 feet. I think that's the most restrictive on the islands for Alaska's ops.