US Told Saudis of Qaeda Plane Threat Pre-9/11
The cable, from the U.S. Embassy in Riyadh to U.S. government officials, said three U.S. officials had met with Saudi officials at Riyadh's King Khaled International Airport on June 16, 1998, "to discuss the Osama bin Laden threat, and press for enhanced vigilance by Saudi security screeners and police patrols around the airport."
...The cable is the latest of several signs made public that U.S. officials had concerns, long before the 2001 hijacked airplane attacks on New York and Washington, that al Qaeda might be targeting aircraft.
Others include a highly classified President's Daily Brief report to former President Bill Clinton dated December 4, 1998, which was titled "Bin Ladin Preparing to Hijack US Aircraft and Other Attacks."
The CIA has also said it had told the Federal Aviation Administration in 1999 that "Osama bin Laden remains interested in targeting U.S. interests including on U.S. territory. He is well prepared to consider kidnappings and hijackings as well as bombings."
On August 6, 2001, President George W. Bush's daily intelligence brief said the FBI had detected "patterns of suspicious activity in this country consistent with preparations for hijackings or other types of attacks, including recent surveillance of federal buildings in New York."