The hijacking of four jets on September 11, 2001, made airline security a top priority in the United States. Now, more than four years later, American lawmakers are asking why airlines - and not the government - are still responsible for checking passenger names against terrorist watch lists. Some new security initiatives have not yet taken off.
Among the security programs that have stalled is one called Secure Flight.
Secure Flight would involve airlines collecting limited information about a passenger traveling within the United States and giving it to the U.S. Transportation Security Administration, or TSA. That information would then be compared to a terrorist watch list. If a name similar to that passenger's is found on the list, the passenger could undergo additional security or, in some cases, may not be allowed to fly.
Nearly $200 million has been spent to develop Secure Flight, and Thursday on Capitol Hill, members of the Senate committee that oversees transportation issues heard from government officials about why the program is still in the developmental stages.
Republican Party Senator Trent Lott from Mississippi expressed the frustration of several committee members.
"We want you to succeed. This is very important work you do," he said. "We want secure flights, but we want some common sense applied in how people are screened and what the conditions are for flying. Let's do some of these programs or forget them. But quit fumbling around with them."
TSA Assistant Secretary Edmund Hawley defended the long time it is taking his agency to launch Secure Flight, saying passenger privacy and data security issues must first be resolved.
"My priority is to ensure that we do it right, not just that we do it quickly," he said.
Cathleen Berrick of the Government Accountability Office says the TSA has made some progress on Secure Flight, but questions remain, including deciding what passenger information the TSA will require air carriers to provide and how it will protect that information.
"Secure Flight required documentation does not fully explain how passenger privacy protections will be met," she said. "And TSA has not yet issued privacy notices that describe how it will protect passenger data for an operational system. As a result it is not possible for us to fully assess how TSA is addressing privacy concerns."
Another program the Transportation Security Administration is developing is Registered Traveler. This program is designed to expedite the security screening process by having travelers voluntarily provide information about themselves that the TSA would verify. If the person qualifies, they would pay for and receive a so-called "smart card," complete with their biometric eye and fingerprints, that would help speed them through airport security. Hawley, of the TSA, said this program is on track to launch by mid-June.
Senators heard from industry executives and civil liberties advocates who had mixed opinions about whether Secure Flight and Registered Traveler should be implemented.
"We absolutely support the concept of Secure Flight, or whatever name you want to give to passenger pre-screening. It's the concept that we support. We don't support at this time Registered Traveler, we think it takes the focus away from where we really ought to have it," said James May, the head of the Air Transport Association of America (ATA), which is the country's largest airline trade association.
Tim Sparapani of the American Civil Liberties Union said his organization thinks both programs should be scrapped.
"It's time for Congress to decide enough is enough. Secure Flight and Registered Traveler will not make us any safer and they will certainly make us less free," he said.
Passenger privacy concerns have slowed the implementation of these programs, but legislators and the aviation industry say they are continuing to work to find ways to enhance security, while causing as little inconvenience to the traveling public as possible.