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E3.2 Takeoff margins
When the temperature is very low, the difference between OAT and flex temperature may
be very large. In this case, the following question may be asked:
.Is the takeoff chart data still useable, and is there still a sufficient margin between the
terrain/obstacles and the takeoff flight path?.
The answer is .YES..
The reason is that:
.
For a given selected flex temperature, the actual OAT does not affect the engine thrust. Therefore, the climb gradient is not modified.
.
For the same IAS, the ground speed is lower when OAT is lower and, consequently
-
The margins with tire speed and brake energy limitations are increased,
-
The TOD and the ASD are decreased.
This signifies that a reduction in ground speed allows a higher margin above terrain/obstacle or a longer decision time than that defined by the regulations.
T/O Net Flight Path at T° (Thrust = TOGA)
T/O Net Flight Path with actual OAT (Tactual) < Tflex = T°
Figure E4
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