Flexible & Derated T/O

Question 1

What is the point of a flexible/derated T/O?

Answer 1

As often TOW

Question 2

How is a flexible thrust T/O achieved?

When can it be used?

Answer 2

You plug in a higher OAT in the FMS (decrease in max thrust available as above Tref) which corresponds to the ‘max’ thrust you require for T/O.
The temperature entered is the flex temp/assumed temp and the thrust produced is the flex thrust.
The thrust produced must be at least 75% of the max available for the ambient conditions (can’t exceed 25% reduction) so there is a Tref max.
Tales is only allowed on a dry or wet (if performance accountability for wet surface is made) RWY, not contaminated.

Question 3

Just remember the following…

Answer 3

Tflex>Tref
Tflex>OAT
Tflex\

Question 4

How is a derated T/O selected?

What is an advantage of a derated T/O?

Answer 4

Is considered a normal T/O as you select a lower max power setting in the FMS, so can be treated essentially as a new engine.
It can sometimes increase MTOW on a short RWY as if limited by ASD due to Vmcg, the less power the engines produce the less yaw produced so a lower Vmcg.
In summary a derated T/O can decrease Vmca/Vmcg as is limited at lower power, unlike flex which has potential to still produce more power. Derated can therefore increase MTOW, but the same can NOT be said about a flex T/O.