Just How Secure Is Airline Security?

April 12, 2005 — -- Picture airline security since 9/11 as slices of Swiss cheese.

No, you haven't stumbled into a gourmet discussion. Bear with me, because there's a very good reason for creating this picture in your mind.

Swiss cheese is noted for its holes, and as much as 30 percent of the surface area of each slice may be taken up by those holes. Just as any security measure we take in aviation has some "holes" in it. Not a 30 percent failure rate (we hope), but some flaws and some ability to fail.

Now, imagine airline passenger screening before 9/11 as a single slice of hole-riddled Swiss cheese, and imagine a type of bullet that cannot penetrate the cheese unless it flies through one of the holes. If that single slice of Swiss cheese security is all you've got standing between the bullet (which represents a terrorist), and seizing control of an airplane or destroying it (which is the bullet's target), as much as 30 percent of the time the bad guys will win.

That's where we were before 9/11.

But what if you add more slices of our imperfect Swiss cheese between the bullet and the target? If each new slice represents a new method of denying a terrorist access, then slice by slice the chances of getting all those holes to line up goes down. Soon -- with enough new slices -- you're close to 99 percent secure, even though each and every Swiss cheese security measure remains flawed and has holes!

This is where we are today with airline security against another 9/11-type attack.

We've added layer after layer of new defensive measures in the airport and the aircraft and on the ramp to prevent a terrorist from ever taking control of a commercial airplane again, and the efforts have been highly effective. (The Swiss Cheese model, by the way, comes from the work of Dr. James Reason of Manchester, England, and is also used in strengthening medical safety against patient injuries.)

So what's changed? Well, first, we got rid of what was clearly a sham of a passenger screening system before 9/11 and replaced it with a reasonably disciplined, standardized, courteous force of federal workers under the Transportation Security Administration. That gave a new, imperfect, but vastly improved slice of security cheese.