Hi 'under obligation not to discuss the specifics of what I hear in briefings. I can legally and factually say that determined attackers with the means, motivation, and demonstrated intent to do harm, sometimes prefer airports as choice targets, and pass them up in circumstances that have been documented.

You can probably find publicly reported instances if you hunt for them, but I'm not going to do your homework for you. I would check up on terror attacks on non-airport targets, and see if any of them considered airports; any search terms more specific would probably be more obscured by noise.

You are correct that lines are a target. It's one of our concerns at the airport. My personal concern is for firearms rather than explosives, though. For the number of people you have to involve in a bomb plot, you can drag that many people and a tenth of the funding into carrying a bunch of guns into an airport. Airports have a bunch of dead ends, often, or long corridors with only two ways out. A couple of people to watch your back, a couple of people to mow down a corridor, maybe double that for the other end, and then a couple of people at the closest exit points to mow down people crowding up to try to escape.

That's the attack I really fear. Mass casualties in a line are tough with a bomb - a blast wouldn't be compressed, and though you'd think closed packed people would just exponentially increase casualties, in reality each body shields those behind them from the blast wave, and channels force upwards, (high ceilings in most airports,) so fatalities don't increase as fast as you'd expect. Crowding you also reduces the lethal radius a bit, creates blast 'shadows'. Packed shoulder-to-shoulder, I would expect around a dozen fatalities and a bunch of injuries, depending on what they were carrying. We don't expect bombers to prefer detonating in line, though we do look for it.', im DAD.