The fragmentation bullets that are to be used by former military personelle ,trained as sky marshalls, disintegrate in tissue like powdered clay. Even if a person is not hit in the brain as preferred in training exercises there is so much damage that infection is often the killer. If the bullet hits the plane it explodes in a cloud of dust and makes no penetrating hole.

20 years ago I submitted an invention to the FBI in Buffalo NY of a hijack prevention technology with the combination of knock out gas and an automatic pilot landing of the plane. Guess what. They are dusting off this old technology and are in the process of perfecting it.