With all of the discussion about arming pilots, and having armed officials on airplanes, this needed to be noded.

The Glaser Safety Slug is a frangible bullet. In that, it is manufactured to ricochet less, have comprable stopping-power with standard bullets, and yet not puncture the hull of an aircraft (No ugly de-compression worries.)

Incidentally, the Glaser Safety Slug was utilised by Federal Sky Marshals in the 70s and 80s, specifically because of these properties.