Mere hours after Germanwings pilot Andreas Lubitz crashed a passenger airplane into the French Alps, killing all 150 people on board, airlines in Europe and North America announced they would change safety regulations so that two people must be present in the cockpit at all times.

What else could airliners be doing to make their flights more secure? Homeland security expert Juliette Kayyem joined Boston Public Radio with Jim Braude and Margery Eagan to discuss. 

"Securing the cockpit door has been absolutely perfect, if the threat is 19 guys or any passenger trying to get into the cockpit," Kayyem said.

"But like all security—and I'm a strong proponent of this—it has to change with the times, change with the risk, change with the threats," she continued.

While it's difficult to anticipate a rogue lone actor—or a "black swan," as security lingo dubs them—there are ways to make systems more foolproof, Kayyem said.

"You never have a single point of failure. Systems have to be built with redundancies and back-up plans," she explained. 

For cockpits, that could mean a system where, if there's a combination of factors like a decrease in altitude and no pilot response, ground control could override safeguards on board. 

"You just have to keep putting up different barriers," Kayyem said.

Want to hear more from Juliette Kayyem? Stay tuned for her new podcast, "Security Mom," which will launch at WGBH mid-April.