Brian Jenkins says there are roughly 100,000 airport workers in the United States alone – baggage handlers, grounds crews, maintenance crews, caterers, cleaners, and more – who have access to an aircraft. Every day.

“Now,” says Jenkins, an aviation security expert and a senior adviser to the RAND Corp., “you tell me. Are we still vulnerable to the insider threat? Yes, we are.”

Jenkins told TravelPulse.com today the ‘inside guy’ theory is becoming more and more plausible in light of the hijacking this week of an Ethiopian Airlines jet bound from Addis-Ababa to Rome. The plane was taken over by a co-pilot who was seeking asylum in Switzerland. The flight landed safely in Geneva and the co-pilot was taken into custody.

Nonetheless, it showed just what one person with access to the aircraft can do and also showed the flaw in the current security system. Security, short and sweet, is designed to keep the bad guys out.

What happens when one of the bad guys is already in?

Jenkins, who in 1996 was appointed by President Clinton to the White House Commission on Aviation Safety and Security and served as adviser to the National Commission on Terrorism from 1999-2000, said the TSA and FAA and the airports have done an admirable job on background screening and security measures. But there’s nothing to account for the worker who goes rogue for whatever reason.

“We simply don’t have a security measure in place for that,” he said. “We have no security mechanism for looking into a man’s soul.”

Doug Landau agreed. Landau is a Virginia attorney specializing in aviation security and litigation, and said it’s a sobering thought.

“We’ve all been through the lines to get into the sterile area, meaning it’s clean of weapons and bombs and bad things. But what about the people in the Air Operations Area (AOA)?” he said. “They do have an ID card system but sometimes after they’re hired and after that initial background check, they’ve done some bad things, or their former homeland splits from the motherland, or they change their thinking, and they’re angry at the big American devil. And what do they have? A pass to get them through to where jet fuel is kept, or to other vulnerable parts of the airport.”

Landau is advocating for airport police, local police, even air marshals to not only sweep the airport, but also what he calls the dark, dank places, the underbelly of the airport, where a lot workers have access to the AOA.

Both Jenkins and Landau said there should be more periodic background and security checks of workers, no matter how much tenure they have.

It has become feasible to funnel passengers through security checkpoints and keep them in a secure area and board them one by one, yes. But it is not feasible to monitor at all times the actions of all of those who have legitimate access to the aircraft.

“From there are you relying on that community of workers in the airport to notice any anomalies,” Jenkins said. “You ultimately depend on the integrity of that population. But you do so knowing that even with those who have highest security levels in the country, you still have the vulnerability.”