Inertia reel seat belts in cars are designed to lock only when
braking/stopping do to impact. Airplanes need support in multiple axis.


Check into that. I don't think it's true.

Cars roll over!



I just checked in my 2006 Honda Ridgeline. Slam on the gas and lean
forward no lock up of the inertia reel.

Tried to produce about the same but opposite "feel" braking and the reel
locked up.

So maybe I'm wrong but it is at least more effective in one vector than
it is in the other.

Having fixed cars over the years I have seen plenty of auto seat belt
reels in various stages of disassembly.

There WAS an early design I saw that used a suspended weight. Decelerate
in any lateral direction and the weight would move and lock the reel.
Newer designs appear to have done away with that system, but they may
still be around. That one would likely not work well in a rolling auto
or airplane.

Newer designs use spinning weights driven outward by centrifugal force.
Does not matter what the attitude of the mechanism. Pull the belt out
quickly enough and it will lock. Many Pipers (including my 74 Cherokee
140) use this system.

Try your experiment in the Ridgeline slightly differently. Instead of
leaning forward, give the belt a quick tug when stepping on the gas.
Likely it will lock then. Who knows, maybe it is of a design that needs
physical deceleration of the locking unit (as opposed to the motion of
the belt).

Good Luck,
Mike