Bush briefed on hijacking threat before September 11 (http://archives.cnn.com/2002/US/05/15/bush.sept.11/index.html), cnn.com, May 16, 2002

According to administration officials,

“President Bush’s daily intelligence briefings in the weeks leading up to the September 11 terror attacks included a warning of the possibility that Osama bin Laden’s al Qaeda network would attempt to hijack a U.S.-based airliner…”

Another official said

“the “chatter” about bin Laden dated back to the Clinton administration but “reached a pitch” in the spring of 2001…”