Originally Posted by mutt
The latest revision to our Brazilian jungle jet has included a 1.2% positive gradient in the acceleration phase with quite severe payload penalties.
FAR 25.111
(3) At each point along the takeoff path, starting at the point at which the airplane reaches 400 feet above the takeoff surface, the available gradient of climb may not be less than—
(i) 1.2 percent for two-engine airplanes;
(ii) 1.5 percent for three-engine airplanes; and
(iii) 1.7 percent for four-engine airplanes; and
Aussie rules (CAO 20.7.1b) say the following:
7.3.1 An aeroplane may be accelerated in level flight from V2 speed to final take-off climb speed at a height above the take-off surface that is the greater of:
(a) 400 feet; or
(b) the height necessary to achieve obstacle clearance in accordance with
paragraphs 12.1 and 12.2.
7.3.2 During any such level flight acceleration manoeuvre, an aeroplane with the critical engine inoperative must have an available gross gradient of climb of at least:
(a) for a twin-engined aeroplane — 1.2%; or
(b) for a 3-engined aeroplane — 1.4%; or
(c) for a 4-engined aeroplane — 1.5%.
Note that the 4 engine gross gradient is 1.5% for both the third and fourth segment - not 1.7% as in FAR/JARs. Anyone know why the difference?
It is the excess
available climb performance that is used to accelerate to final climb speed.