The most notable attempt was a FedEx DC-10 in 1994,
where a disgruntled worker who was going to be fired attempted to kill
all three crew members and crash the plane into FedEx headquarters

IIRC that was motivated not by any overt act of terrorism but by the
wacko's plan that his kids would collect on his life insurance policy
if he died in a company acft. Of course, this wouldn't matter to the
people on the ground where the plane came down..