Ramzi Yousef bombs Phillippine Airlines Flight 434
On December 11, 1994, Ramzi Yousef planted a small bomb aboard a Phillippines Airlines airplane.
He assembled the bomb from components that he had snuck aboard the airliner. Yousef set the timer for four hours and then hid the bomb below his seat. He got off the plane at a stopover and the bomb exploded once the plane was back in the air. One person was killed, several more injured, but the pilot was able to land the plane. Yousef used this as a trial run for future terrorist attacks that he and his uncle, Khaled Sheikh Mohammed hoped to initiate.
Khaled Sheikh Mohammed met with bin Laden in Afghanistan at told him of plot to train pilots to crash airplanes into buildings.