BGS, I think you've found another of the glaring inaccuracies in that book. Seriously, I've seen a copy of it, and if I'd paid for it I'd be demanding my money back!
As far as I know no twinjet uses contra-rotating engines. What's the point? As there's no assymetric blade effect, it really matters not a jot which way they spin. (excepting of course torque/gyrospic effects, but that's a different matter entirely!)
If I went into an interview talking about "critical jet engines" (other than "the furthest one from the fuselage") then I'd be laughed out of the room, and rightly so.