Much is made about pre-9/11 reports of al Qaeda's plans to hijack US airliners, and the Clinton and Bush administrations' lack of response. Hindsight is wonderful, but the fact is that US airport security was excellent before 9/11 -- so good that there had only been one fatal US hijacking between 1970 and 2001.
7 December 1987; Pacific Southwest Airlines BAe146-200; near San Luis Obispo, CA: A recently fired USAir employee used his invalidated credentials to board the aircraft with a pistol and apparently killed his former manager and both pilots (USAir had recently purchased PSA). All five crew members and the 37 other passengers were killed.Additionally, there had been exactly 3 fatal hijackings involving US carriers overseas (Rome, Athens and Karachi) in that period. So, even foreign security of US carriers was pretty good regarding hijackings, and Rome and Athens, at least, were unlikely to see a repeat.