Maximize casualties by blowing up an aircraft over an urban area.
In slummy Detroit in a high noise zone (constantly incoming aircraft)? I don’t think ground damage was the point.
On another thread, Fivecatsandadog advised that there’s not much density around Detroit Metro. A DC-9 flying out of there crashed just after takeoff and only killed 2 people on the ground, even though the crash killed 154 passengers and broke the plane up so badly that only the flight recorders were of any use in the investigation.
But then, the spectacle of a crash on Christmas with hundreds of deaths would be more than enough for Al Qaida’s purposes.