alt Hacker NewsFrom his house, no I don't think a consumer mortar could hit a plane. The planes weren't that low.
But the area surrounding the airport is very densely populated. Given all those people, I'm not surprised some dumb kid (or adult) lit fireworks near the airport.
Also, most fireworks are illegal in Illinois. But it's only a 30 minute drive from Chicago to Indiana.
I haven't lived in Indiana in over 20 years, but is the law for mortars still:
Legal to posses
Legal to buy and sell
Not legal to use
That was always a bit silly to me. Stores would even have you sign a waiver that you weren't going to use them in Indiana.