I'm sure that, somewhere in the deep and distant past, I've come across reference to jet ac having a critical engine in the context of a X-wind and the ac's weathercocking tendencies. Most ac (I think) have a positive tendency ie they tend to turn into wind if left unchecked and, thus, failure of the upwind engine would pose the more handling difficulties. Conversely, the HS/BAe 125 Series 4 to 700, for example, have a negative tendency due to the ac geometry and therefore the downwind engine's failure is critical. Unless, of course, you know different!!
Cheers,
mcdhu