Understanding Flaps

Hi all, Ive noticed that people can get quite confused about flaps on the simulator so I decided to create a small tutiorial.

#Understanding Flaps

Firstly there are so many aircraft with different approach charts and flap levels. I’ve noticed in the simulator that some aircraft have flaps 5-10-15 etc or 5%-15% etc. In this tutorial I will be explaining the flap levels in 5-10-15, its not hard to convert.

Whats the purpose of flaps?
The purpose of flaps is to give a lift at much slower speed. Not only is flaps used for takeoff, but also for landing since it can also help the aircraft maintain slower airspeeds without stall.

Where are the flaps located?
The flaps are located on the left and right wings, both front and back. The diagram below shows the wing of an A320/19/18. Other aircraft like a Cessna and smaller aircraft do not always have these features.


Before takeoff you must have you flap level set and ready to go, if you follow a checklist it should display the proper procedure to taxi. The recommended flap for takeoff is: Flaps 1, depending on your aircraft. By following the takeoff procedure you should perform a smooth takeoff. Taking off without flaps can lead to runing off the runways end, since it doesnt give the necessary lift for your aircraft or you don’t maintain a fast enough speed in time. The chart below will not only guide you through takeoff but show the necessary information about flaps on takeoff and after, (This diagram shows the proper procedure, some info may not be applicable:


From this part on, it really depends on your type of aircraft. Whatever the aircraft though, if its an A320, B737-800, B747 etc, there is always a chart to show when certain procedures should be applied. The following chart is for a perticular aircraft but gives you an idea of where and when flaps should be applied.



(Donated kindly by @ATK)

It is also very important to follow the correct speeds when appling flaps. It depends on your weight and blance as well, since it can affect your speed and how well you descend/ascend.

This is an example for a B737-700/800/900:


Hope this helps!

Cheers Oli H


You may want to change the example for the 737 to one for the 700/800/900.


Interesting. I never knew there was that many components associated with flaps.

It just depends on your aircraft. :) I was quite surprised to when I first learnt about it.

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Max Ask’s: What’s the difference between a flap and a slat? Are there leading edge & trailing edge slats what’s there fungtion? What about spoilers?
How do they relate to flaps & slats? I note an air brake on the diagram, is it interconnected to the slats/flaps or does it operate independently?

(@Max… Misprint/Typo. Not addressed to you my error. Sorry)


Firstly, be careful 5% isn’t a good figure. It is not equivalent to 5°.
When flying Airbuses, flaps 1+F is equivalent to 8° flaps and 20° slats.

Then, flaps ‘1’ (1+F to be accurate) isn’t always recommended. It can be 2 and even 3. For Boeing, it depends the aircraft but it usually goes from 5° to 20°.

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What is “F”?

I believe the F is for 10 degree flaps.

Its hard to explain, but you are correct. I was trying to reword every few seconds when I was creating it, since some figures weren’t correct.

One is at the back, one is at the front of the wing. They both help generate a lift for the aircraft :)

Spoilers are a little different from the flap system, even if they were shown on the diagram. It intentionally spoils the lift.

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@Skylines… Good man sky… Just pulling your chain. You got it…

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8° to be exact sir!


I thought the so called Flap Tracks were called Pylons. I’m guessing it’s the same thing anyway. Nice Tutorial BTW! ;D

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No wait, that’s what holds up the engines… :)

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The 737NG is a bit more forgiving on flap extension speeds than the classics which is what you posted.

Can set flaps 1, 2, and 5 at or below 250 kts
Can set flaps 10 at or below 210 kts
Can set flaps 15 at or below 200 kts
Can set flaps 25 at or below 190 kts
Can set flaps 30 at or below 175 kts
Can set flaps 40 at or below 162 kts

To add to your approach profile diagram, I have one which I annotated myself and may be of some use. This is a fairly typical 737 approach profile with speeds, flaps, and gear deployment shown. It is a CAT I ILS approach. Obviously in real life it would depends on all sorts of factors to what the VREF and final approach speed VAPP is. This is copied from a real world FCOM albeit with some annotation added by me.



@JFKPlaneSpotter101, they are also called anti-shock bodies.


Excellent stuff everyone! Many, many thanks!

@ATK I read somewhere, I forget where now, that for most 737’s flaps 40 is rarely used, that they usually land with flaps 30. Also, the more wind, the less flaps are needed for both take off and landing.

What I’ve been doing is setting flaps to keep the little pip in the HUD (forget what it’s called) almost level with the horizontal pitch line during approach.

I think both are true - although specifics can differ from airline to airline. Generally flaps 30 for landing unless doing an autoland in low vis when flaps 40 is recommended. I think I have seen somewhere at least one airline’s fcom said flaps 40 all the time though.

The more headwind you have I think the less flaps you need, although for landing only 30 or 40 are normal and for take-off 1 or 5 are typical.


Very helpful information.