Microburst2002:
The question is "How the heck I know the airplane is unflyable?"
Short answer: You probably don't.
TWA lost a 707 at KCVG in 1967 because after V1 the F/O mistook as an engine failure the momentary noise and buffeting from passing through the engine wake of a DAL DC-9 that was stuck in the mud and trying to power his way out.