Posted by: Korry | November 1, 2011

Techie Tuesday: When do you deploy the flaps?

For the inaugural edition of Techie Tuesday, I’d like to answer the first technical question I received from a reader. This question comes from David in Philadelphia. David asks, “When do you start to deploy the flaps? Is it an airspeed thing, a combo of airspeed, distance to airport and altitude, is it a set angle or do you do it by feel?”

If you’re wondering what a wing flap is, you’re probably not alone. The flaps are typically the inboard section of the trailing edge (back) of the wing. Here’s a picture that may be helpful.

Extended Wing Flaps

Flaps create lift as well as drag. Normally, flaps are used to help an airplane fly at a slower airspeed. This is why you see an airliner lower the flaps for takeoff and landing.

To answer your specific question, David, on landing, we deploy the flaps predominantly based on airspeed. Each flap setting, measured in degrees, has specific maximum airspeed limits. Additionally, based on the weight of the aircraft, there are minimum maneuvering speeds as well. If ATC directs us to fly at a slower speed than our current minimum maneuvering speed, we need to extend more flaps. Sometimes, pilots will use the flaps to add drag to help descend at a faster rate, but most of the time it has to do with the desired speed flown.

Obviously there is a sweet spot. More flaps lets us fly slower, but that also adds drag which means a higher fuel burn. So left to our own devices, most pilots will choose to fly “clean” (which is to say without any flaps deployed) until it is necessary to begin slowing down for landing. Otherwise, we are probably not flying as efficiently as we could.

Hope this helps to answer why we deploy the flaps when we do!

Do you have a question for Techie Tuesdays? Email me at and ask away!



  1. […] dangerous to do in the real world such as engine failures and fires, blown tires, landing gear or flap malfunctions, etc. All of those “failures” are controlled by the instructor who sits at […]

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