This is a very subtle bug, or perhaps it's a design decision and not a bug at all. The issue is related to how damage that you receive from the front is supposed to turn tail damage into engine damage and shots from the rear do the reverse.

This is ignored in certain cases when the shooter is an observer who is shooting sixty degrees to the side of his plane. If he hits an enemy on the nose or tail, the damage is applied as if he hit them in the side (that is, engine and tail damage is applied as shown on the chits and not converted).

I think I know why this happens. The damage conversion appears to use the same calculation that decides if the deflection modifier should be applied to the damage roll. There is a passage in the rules that says that observers only avoid deflection if they're shooting directly to their rear at a target headed towards them or directly away. I suspect that's also the only situation in which the engine/tail damage they do to their target gets converted.

So, what do you think, should the engine/tail damage conversion be applied in the 60 degree situation? Or should it remain as it is, with the use of the damage conversion always occurring only when there is no deflection modifier?