Hi, nice discussion going on about segments. Here is my understanding about this:

Assuming critical engine inoperative, the four segments are:

First Segment: The Climb from 35 feet point until the landing gears are fully retracted. Conditions in this segment are:

- landing gear extended

- flaps in T/O position

- Speed = V2

- Climb gradient for 2 engine A/C = Positive

- Climb gradient for 4 engine A/C = 0.5%

- Takeoff power

Second Segment: Climb from gear retraction point until a height of 400 feet is reached. conditions in this segment are:

- gears retracted

- flaps in T/O position

- speed = V2

- gradient 2 engine a/c 2.4%, and 4 engine a/c 3.0%

- takeoff power

Third Segment: Its the horizontal distance covered after the second segment until the flap retraction speed is reached, to raise the flaps plus the distance required to accelerate the aircraft to the flaps up climb speed. It consists of two parts:

First part of 3rd segment: Distance covered before flap retraction, accelerating to flap retraction speed. The conditions are:

- gears retracted

- flaps in t/o position

- speed increasing from v2 to flap retraction speed

- gradient 2 engine a/c 1.2%, 4 engine a/c 1.7%

- takeoff power

Second part of 3rd segment: Distance covered after flap retraction, accelerating to final t/o climb speed. the conditions are:

- gears retracted

- flaps retracted

- speed, accelerating from flaps retraction to final t/o climb speed

- gradient 2 engine a/c 1.2%, 4 engine a/c 1.7%

- maximum continous power

Fourth Segment: the Climb from 400 feet till 1500 feet is reached, after the end of third segment operating with max continous power. The conditions are:

- gears retracted

- flaps retracted

- speed = final t/o climb speed

- max continous power

- gradient 2 engine a/c 1.2%, 4 engine a/c 1.7%

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Regards