I don't believe FF's theory about the demonstrated x-wind relating to a landing with no correction.
I've heard this theory many times, but never seen anything written down. However, consider the Piper Seneca. I believe that most variants have a demonstrated x-wind of 17kt (please correct me if I'm wrong, though - I've only flown two variants, and not seen the manual for the others).
The exception is the first variant, which has a demonstrated x-wind of just 12kt. The difference between this and the other variants is that, in the early version, the ailerons and rudder were connected to each other, making it more difficult to use the crossed controls necessary to carry out a x-wind landing. This would seem to be counter to FF's theory.
(I don't know if the rules are different for larger aircraft, though, as 1013 suggests.)
FFF
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