The flight numbers that were hijacked are 11, 93, 175, and 77.
11 is yesterday's date, 9+3 =12 which is today's date, 1+7+5 =13 which is Thursday's date, and 7+7 = 14 which is Friday's date. I pray that this is only a freak coincidence.
Well, if you keep up the logic, you should have used 1+1 =2, or 10 days ago.
The planes were picked because of their departure times, location, and the fact that they were loaded with fuel. I doubt numerology came into the picture.