Last July, John Dean's column at Findlaw.com pointed to this footnote in the Report of the Joint Congressional Inquiry Into The Terrorist Attacks Of September 11:
"National Security Advisor Condoleeza Rice stated in a May 16, 2002 press briefing that, on August 6, 2001, the Presidents Daily Brief (PDB) included information about Bin Ladins methods of operation from a historical perspective dating back to 1997. One of the methods was that Bin Ladin might choose to highjack an airliner in order to hold passengers hostage to gain release of one of their operatives. She stated, however, that the report did not contain specific warning information, but only a generalized warning, and did not contain information that al-Qaida was discussing a particular planned attack against a specific target at any specific time, place, or by any specific method."
--From pdf page 79 of "Part Two -- Narrative -- The Attacks of September 11, 2001" {297 KB PDF} at
http://news.findlaw.com/hdocs/docs/911rpt/Dean says in his Findlaw column,
"What exactly did {the August 6th Presidential Daily Brief} say? We cannot know. But the Inquiry's 9/11 Report lays out all such threats, over that time period, in thirty-six bullet point summaries. It is only necessary to cite a few of these to see the problem: In September 1998, the {Intelligence Community} obtained information that Bin Laden's next operation might involve flying an explosive-laden aircraft into a U.S. airport and detonating it.
In the fall of 1998, the {Intelligence Community} obtained information concerning a Bin Laden plot involving aircraft in the New York and Washington, D.C. areas. In March 2000, the {Intelligence Community} obtained information regarding the types of targets that operatives of Bin Laden's network might strike. The Statute of Liberty was specifically mentioned , as were SKYSCRAPERS, ports, airports, and nuclear power plans.
In sum, the 9/11 Report of the Congressional Inquiry indicates that the intelligence community was very aware that Bin Laden might fly an airplane into an American skyscraper. ..."
--From
http://writ.news.findlaw.com/dean/20030729.htmlThe 36 bullet points Dean refers to are also in the online Joint Inquiry Report at the URL given above, in pages 71-80 of "Part Two -- Narrative -- The Attacks of September 11, 2001"