[mikegi]

b) The hijackers might have had a small bomb.

The hijackers probably said they had a bomb to discourage a passenger revolt.

[eno_]

AQ previously experimented with improvised explosives, like peroxide-acetone bombs and killed a Japanese passenger on an airliner over the Pacific with such a a bomb.

Then we caught the shoe bomber.

In this case, a bomb would have ejected debris far from the main crash site, which is what incontrovertably happened here. So a bomb is one way to explain what happened. A shoot-down would also explain it.

But there is no possible way that just flying the plane into the ground would have resulted in small debris, including human remains, miles from the main crash site.

[Pukka Puck]

"The hijackers probably said they had a bomb to discourage a passenger revolt."

Bingo!