DENVER -- The foiled Christmas Day terror attack aboard an airliner bound for Detroit has renewed the debate about airport security, raising questions about everything from how tickets are sold to how passengers are screened.

By many accounts, suspect Umar Farouk Abdul-Mutallab should never have even made it to security. The Nigerian man purchased his ticket with cash. He bought a one-way ticket. And he had no luggage. Aviation experts said those three items were red flags and should have prevented the suspect from flying.

"We need better education to people selling tickets, and I'm advocating the elimination of selling tickets for cash," said Steve Cowell, an aviation analyst.

But Cowell said that is only one change he suggests to make the skies safer. He said interagency communication also must improve.

Abdul-Mutallab was on an advisory list but, despite his father's warnings to U.S. Embassy officials, he never made it onto more restrictive lists that would have caught the attention of U.S. counterterrorist screens. The United Kingdom had banned the suspect from flying.

"Terrorism is not just a Denver problem, not just a United States problem. It is a worldwide problem, and this database integration needs to be addressed worldwide," Cowell said.

But the no-fly lists are not accurate, and the Transportation Security Administration said they are working to correct that with a new program called "Secure Flight." It should solve some misidentifications and other problems with the list.

American Airlines is already involved in the "Secure Flight" program. All airlines must be involved by November of next year.

Additional security measures, such as the full body scanner that can see through clothing, also are in place at some airports. Six airports in the U.S. use the devices for primary screenings. Denver is one of 13 airports that use the high-tech body scanners for secondary screenings, typically for people who have set off the metal detectors.

And there is renewed debate about using profiling as a way to ferret out terrorists. Proponents say profiling works, but others say it makes suspects out of innocent people.

"Profiles have worked to a certain extent, and then common sense really has to be integrated in there," Cowell said.

But, he said, in the failed Christmas Day attack, "Common sense wasn't even a part of this equation."

A spokeswoman for Delta Airlines said they followed all FAA requirements.

"That wasn't good enough," Cowell said. He said the pre-screening process needs to change. Abdul-Mutallab should have been red-flagged in the pre-screening process, he said.

"This person met every single criteria," Cowell said, "and they were able to board that airplane. Why did it not work?"