How do I figure out take off flaps setting?

[Guest kjolsnes]

Gents,What are the steps I need to take to figure out if I should use 5,10 or more flaps for the take off?Have found pieces of info around but could anyone give me the details for a 747-400, how you could determine this?Thanks in advance.Kjetil ONorway

[Balint 18]

Kjetil,Not sure how it's done IRL. I usually go for 20 on a normal/heavy loaded aircraft and use 10 when it's really light. Also, whenever possible, I use derated thrust for takeoffs and climbs to keep the engines durable for a longer time (I suppose as they do it IRL).So even if the aircarft is not fully loaded, I tend to use Flaps20 as it gives me lower V1, VR, V2, and eventually helps compensating derated thrust.Cheers,

[Guest alexhn]

Usually T/O flap setting is determined by company Standard Operating Procedure. I think most use flap 20.