If I remember correctly the regulations also included allowances for higher approach speeds and touchdown point.
CliveL,
That's how I remember it as well, in general terms, perhaps somebody with a better memory or library could expand. Doing ARB Performance A was a long time ago.
What I also remember was that the ARB factors were smaller than CAB/FAA figures, and the bottom line was that the final figures wound up being very similar ---- a quite complex (but line operationally realistic) test requirement with small buffers, versus a simple test requirement with a big buffer.
Tootle pip!!