I don't know how much faith I'd put into your hypothetical.
I'm not implying the terrorist threat is large – it's really, super small. But just because they haven't done THAT yet, doesn't mean they won't. So far, in the US, what they've done is sneak explosives onto planes.
So far what muslim terrorists have done a couple of times is to sneak explosives onto a few planes and fail miserably (shoebomber etc.), or storm the cockpit, or blow up bomb far away from airports (Boston bomber, '93 WTC bombing etc.). The storming the cockpit scenario was rendered totally pointless to try again after 9/11, and the explosives attempts have been rather weak.
Overall, bombs and shoot-outs not related to planes at all has been responsible for the vast majority of the most lethal terrorist attacks in the US apart from 9/11, both if you look at muslim terrorists separately, and other attacks in recent history.
I'm not implying the terrorist threat is large – it's really, super small. But just because they haven't done THAT yet, doesn't mean they won't. So far, in the US, what they've done is sneak explosives onto planes.