Question re Climb Segments specifically segment one.
Where does it begin at VLOF or 35ft
Jay Bo,
Segment 1 begins at 35' ("screen height" for a dry runway). Everything before this is considered to be the takeoff run. Yes, there is something that begins when the wheels leave the pavement, but that is not called "first segment". See below.
It would probably help you to look at some performance tables from the AFM for an aircraft >5700 Kg MTOW. The takeoff tables give figures for at least 3 distinct stages:
1. The takeoff;
2. The first segment;
3. The second segment.
For the takeoff stage, you will see distances published. These distances are the horizontal distance from brakes release to screen height (a point also known as "reference zero"). This point is at 35' for a dry runway, and 15' for wet.
The first and second segment tables give the horizontal distance that will be consumed during those stages, and also the height that will be gained (and the gross gradient).
The preamble to these tables defines precisely where the segments start and end. Logically, the first segment has to commence at the point where the takeoff ceases ("reference zero"), and if you peruse the preamble to these tables, you find that the first segment has indeed been thus defined.
But, this is how the manufacturer is presenting the performance and it may not be precisely aligned with how regulatory authorities (e.g. CASA) stipulate required performance. Indeed, and as you have seen, CASA don't refer to the takeoff in terms of segments.
Regs 20.7.1B mentions nothing about 35ft only the speed it becomes airborne.
This is paragraph 7.1 of CAO 20.7.1B. This paragraph is referring specifically to the stage that ends when the gear is retracted. They don't use the term "first segment", but they are referring to the same performance requirement (which, for twin engine aeroplanes is a gradient of climb that is merely
positive).
You would note that this CASA requirement applies from when the wheels leave the runway through to when the gear is fully retracted, which, in terms of the commencement point, is different to the "first segment" as defined by the manufacturers.
This difference is not relevant. Perhaps you could tell me why it is not relevant. That would make for an excellent exercise that would force you to acquire considerable understanding of takeoff performance theory!
However in my training notes Avery and AFT it says segment one from 35ft to gear retraction.
In a practice exam by ground effect aviation they have it as from lift off to gear retraction.
The difference depends on the context. If the context is CAO 20.7.1B, then the latter is the more relevant. If the context is not about CAO 20.7.1B, but is more about takeoff theory in general, then the former would be the more relevant.
One very important thing to keep in mind about segments. This should help prevent them becoming confusing:
They only apply with one engine inoperative. With all engines operating, they are not applicable.
Here is something else that is useful to keep in mind. The Vr speed is chosen by the manufacturer so that the aeroplane will achieve V2 speed at precisely the screen height, when one engine is inoperative. The manufacturer chooses all those V1, Vr and V2 speeds. For a takeoff with given conditions, he establishes V1 and V2 speeds first, then Vr last.