RE:
I was wondering what the FARs say about that, but can't find a requirement for a "blade off" test for props.
§25.875Reinforcement near propel-
lers.
(a) Each part of the airplane near the
propeller tips must be strong and stiff
enough to withstand the effects of the
induced vibration and of ice thrown
from the propeller.
(b) No window may be near the pro-
peller tips unless it can withstand the
most severe ice impact likely to occur.
I'm guessing if the procedure is to not stop the props, the Beechcraft folks are quite sure props aren't going to go into the cabin. Just a guess.
The only requirement for consideration of an "uncontained" prop blade is similar to the same for any uncontained bits from inside the engines as well.
in simple terms, the aircraft systems need be designed to be, redundant, or shielded, to a
practical extent, from the debris.
However, it is
not practical, to provide any meaningful protection from a whole prop blade release anywhere in line with the prop swath, end of story.
by-the-way, in the case of props striking the pavement hard enough to break off, their tangential acceleration and hazard to the cabin will be greatly reduced.