Qantas744ER From United States of America, joined Jun 2005, 1401 posts, RR: 3 Posted (10 years 5 months 1 week 4 days 14 hours ago) and read 3583 times:
Hey, i have a question regarding Flap settings on the 747-400: The available Flap settings on a 747-400 are 10 and 20, for example Qantas only uses 20.
What is the reason for this? Does United Airlines only use 10? becuase on takeoffs the 744 always seem to have that setting on UA?
Grbld From Netherlands, joined Dec 2005, 353 posts, RR: 2
Reply 1, posted (10 years 5 months 1 week 4 days 14 hours ago) and read 3572 times:
This is mostly due to the operating philosophy of the airline and in individual instances due to performance issues at an airport. If the flaps are extended more, you will be able to rotate and lift off at a lower airspeed, thus using less runway (which may sometimes be required) and also have less wear and tear on the landing gear. However, this higher flap setting (farther extended) also means that your climb performance is worse than with a lower flap setting (less extended). So in some cases where runway length isn't an issue, but there may be obstacles in the climbout path, a lower flap setting may be desired.
Other than that, it does depend on airline philosophy.