Ed Ballinger, a flight dispatcher for United Airlines, is continuing to send messages one by one to the 16 transcontinental flights he is covering, warning them of the first WTC crash. He is handling both Flights 175 and 93, and 175 has failed to respond to his message. A few minutes after 9:00, he sends a message to Flight 93. The exact content of the message is not known, but apparently it doesn’t advise the pilots to bar the cockpit door. [Pittsburgh Post-Gazette, 10/28/2001; New York Observer, 6/17/2004]
http://www.observer.com/node/49415

Another flight controller at the Cleveland tower in charge of Flight 93 at the time later recalls, “I saw controllers step up to the plate and start warning flight crews. This was totally by the seat of their pants. It’s not because they’re directed to by anybody. It’s just, OK, everybody’s on alert right now.” [MSNBC, 9/11/2002]

Ballinger later says, “One of the things that upset me was that [the FAA and United Airlines headquarters] knew, 45 minutes before [Flight 93 crashed], that American Airlines had a problem. I put the story together myself [from news accounts]. Perhaps if I had the information sooner, I might have gotten the message to [Flight] 93 to bar the door.” [New York Observer, 6/17/2004] Ballinger will send Flight 93 a second, more detailed warning that does warn to bar the door. It will reach Flight 93 at 9:24 a.m., shortly before the flight is hijacked.