A33Zab,
IMHO the FCOM explains the reasoning behind the selection of 8.6 degrees. Once chosen, this value limits the usability of the BUSS to below FL250. Higher altitudes require lower values of the S/W threshold, which would have impaired the usefulness of the system at low altitude.
Last edited by HazelNuts39; 7th July 2012 at 11:48.
Reason: clarification