1994: Senior al-Qaeda member Khalid Sheikh Mohamed and others develop a plan to place bombs aboard up to 12 flights - an attack codenamed Operation Bojinka that is disrupted when Filipino authorities raid the plotters' apartment.

September 11, 2001: 19 al-Qaeda members hijack four passenger jets, flying two directly into the World Trade Centers in New York and a third into the Pentagon building in Virginia. Passengers on a fourth flight overwhelm the hijackers, forcing the aircraft to crash into a field in Pennsylvania. Nearly 3,000 people are killed.

December 22, 2001: An attempted attack by British citizen Richard Reid on an American Airlines Boeing between Paris and Miami is thwarted by the crew and passengers. Reid, who allegedly trained with al-Qaeda, hid the explosives in the soles of his shoes and tried to light them mid-flight.

2003: Al-Qaeda plans to hijack jets leaving London Heathrow airport and to crash them back into the airport and into a highrise building in London's Canary Wharf business district.

August 10, 2006: British police raids result in the arrest of 21 people accused of plotting to blow up airliners flying between the US and Britain over the Atlantic Ocean using explosives made from liquids. The plot results in new restrictions on what passengers can carry on board.

December 25, 2009: Passengers aboard a Northwest Airlines flight from Amsterdam to Detroit overwhelm a Nigerian man who set off an explosive device as the flight came in to land. The device was quickly put out and no one was harmed.