Selecting flap settings and Vref

[pipper 0]

Hello to the community......I am having difficulty finding out how Vrefs and flap settings are chosen for my 737-700. I know how to select them in the FMC but I do not understand how one is chosen over another. For instance, when do I choose landing at 40 flaps vs. 30 flaps vs. 25 flaps?Where does gross weight fit into the picture? Obviously a flaps 40 landing and Vref is slower than a flaps 25 but I am unclear as to when I should choose a flaps 25, etc. I can guess that shorter runways would dictate a slower approach so that a shorter landing roll would occur, but I am not sure about other factors. Are there any guidelines for visual type approaches where alot of maneuvering is involved ie- the KJFK VOR 13R/L? Many kind thanks in advance, Joe Swier

[Guest meyomyx]

Hi JoeThis has been covered a few times. If you haven't seen Brad Marsh's Geezer guide to the 737NG then download it and run thru it a few times. As I understand it, individual company's SOP's will determine "normal" flap selection.You're right that 40 flaps will fly you in slower but at the penalty of more drag ... so you'll get into shorter fields. More difficult to clean up in the event of a go around (slow and draggy) and not an ideal configuration in gusty conditions! I know that some airline SOP's don't use 40 flaps routinely for that very reason. Others use 40. I normally use 30 - try a go around with 40 and see the difference.As for flaps on a busy approach - well at JFK you'll likely be flying at a prescribed speed ... and the flap setting for that will depend on loading etc. 190-220 are reasonable figures but you should be extending your flaps at around 200 in any case - the flap indicators on the FMC should be your guide. You should be flying at flaps 5 with 5 miles to go before GS capture ... probably around 180-190kIf you see Brad (Zapper) around this forum, ask him more - he flies these things.Hope this helps

[Guest tmetzinger]

Increasing the flap setting does two things aerodynamically - it increases lift and increases drag. This means you can (and WILL) fly more slowly before stalling, and you can land in shorter distances. It also means that you need more thrust to obtain lift, and can make go-arounds or single-engine work exciting or impossible."Normal" landings generally use 30 degrees of flaps, but you may use lest in gusty conditions when runway length permits. Each operator has different standards for landing flaps.

[Guest Knikolaes]

Hey I do not believe I have that guide. Know what the link is to that Geezer's Guide?

[Guest Michael_H]

Here you go:on the left side.http://homepage.powerup.com.au/~speedy/

[Guest Knikolaes]

Awesome MANY thanks!!!

[pipper 0]

Thanks to Nick and Tim....apologies for not responding as fast as you did to me because my cable modem died! Ugh!Anyways, I do have a copy of the Geezer guide which I agree is a very good read. But it didn't answer in a more specific way the reasoning for using 30 flaps V 40 flaps. I saw the procedure where two weights were subtracted on the progress page and then further subtracted from the GW on the INIT REF page, but the reason WHY a specific flap setting was chosen was not mentioned at all. I do most of my landings at flaps 30 unless I am landing at a very short runway like KSNA which I think is under 6000 feet and in that case I fly flaps 40. I guess the pros have company manuals which specify how to do this. Cheers and again my thanks for your time!Joe Swier

[Guest Knikolaes]

Actually, Joe, you nailed it right on . . . . Most companies indeed have manuals specifying their preferences, but most of them will say flaps 30 unless you have a really short landing, so you are actually practicing more in procedure than you had thought.A lot of people try to overkill and think there is some rocket science to choosing flaps and such while flying. Really it is as simple as:"The shorter distance you want to land - the more flaps you use."That's it. The SPEED of your landing may be off weight, but the more flaps you use the slower all the speds will be no matter what.The aircraft manual itself, not the company manual, will dictate the speeds that the AC will handle for Vref. It's all entirely based on how much speed the flaps can handle with weight being the secondary factor - the factor you take into account to not stall and fall like a brick.

[pipper 0]

Thanks Chris for your response.......I guess we can make things overly complicated indeed. Apparently sometimes common sense is all it takes! I just wanted to make sure I was more or less doing things the way the real boys do. The forum really helps you do that and for that I am very grateful!Cheers again.......Joe