We were both Trustees for Embry Riddle Aeronautical University, which Al strongly supported, and he was a true advocate for Business Aviation as the National Business Aviation Association launched its No Plane, No Gain program in the 1990s.

FORBES: He Brought Safety To The Skies

Chuck Eastlake, a professor of aerospace engineering at Embry-Riddle Aeronautical University in Florida, said the technology for the reinforcements seems to be relatively basic.

CNN: Airlines move swiftly to secure cockpits

"More than 28, 000 flights take off each day in the United States, so if you look at the statistics, they're pretty small in relation to the big picture, " said Kees Rietsema, department chair of business administration at Embry-Riddle Aeronautical University.

CNN: Air rage: Passengers 'quicker to snap'