Here is an interesting reason for a delay, then a flight cancellation.
July 6, 2010, DFW. Our AA Flight was first delayed for an hour. Flight then cancelled, and the mad scramble to get on a later flight, which failed.
We later learned what happened. (Or maybe this was a lie, who knows?)
Someone at DFW tower/ATC is reported to have spotted a funnel cloud (yes, it was raining) within some distance of the airport, and they did what SOP required that they do. Abandon the tower until the all clear was given.
That ended up in over 100 flights being cancelled, all airlines.
Was anybody else in DFW on 06 July about the middle of the day with a similar problem? We ended up spending the night on my dime, and AA didn't do as they'd promised when I went to the desk, which was to keep my bags in DFW and let me carry them back on.
Rant, not quite about flight cancellation ...
No, they just sent them on to destination ... even after stating to me, with the little computer bar coded tickets in my hand as I spoke with the desk agent that they'd take them off so we'd have our stuff when we spent the night.
Side issue, but annoying as hell when they lied to my face and it took me two hours of phone calls, beyond the hour of waiting for them at a baggage area for bags that never showed up (me and bout fifty other people who'd been promised the same ... ) to figure out where the hell they were.