Firstly,
a bullet hole in the fuselage of a plane will not depressurize the cabin. It won't do much but make an annoying noise that can be easily "patched"
with something as simple as a pillow. The plane's pressure regulator, which is automatically activated any time there is a change in ambient air
pressure (such as with a high or low pressure weather front), will handle the minimal pressure difference caused by such a small hole.
Secondly,
Sky Marshals are equipped with a special kind of bullet called
frangible
ammunition. The link will explain in detail what frangible ammunition is, but in brief it is designed to fragment on impact with little
ricochet. It won't penetrate the fuselage or the cabin windows. Specifically, US Sky Marshals use
Glaser Safety Slugs, which are a type of frangible ammo.
Between the frangibles, bean bag ammo, and rubber bullets, the Sky Marshals have many options other than your standard full metal jacket shell.
Yes, there are risks and hazards. But the
training and qualification a Sky Marshal is
required to have makes "accidents" less likely. In the interest of security & safety, I really think they've made the best choices possible.
-B.
