Secondary barriers, supporters say, would give crews more time -- approximately five seconds -- to react to threats. Prior to opening the cockpit door, flight crews would deploy the barrier, temporarily securing the space directly in front of the cockpit door.
"It's not an impenetrable barrier," Powers said of the device. "If somebody attempted to breach it, that would, one, give everyone an indication of that individual's intent and, two, delay them long enough so one of the flight attendants could shut the flight deck door."
Despite the barriers' perceived benefits, the FAA has yet to mandate them, largely because of the cost of the devices -- about $5,000 to $10,000 per barrier.
"Right now, we don't see a need for it," FAA spokeswoman Alison Duquette said, adding that the post-9/11 security measures the FAA and TSA currently have in place, such as improved screening technologies and increased air marshals, have been sufficient.
This doesn't mean the FAA has dismissed the barriers altogether. In 2008, the administration petitioned to establish a committee that includes representatives from the FAA, airlines, and airline trade associations. Folsom, a co-chairman of the committee, said the group is currently working on a report that will outline minimum performance criteria, installation instructions, and other issues for secondary barriers. Folsom said the committee is on track to complete the report this September, around the 10th anniversary of 9/11.
Although a federal mandate for secondary barriers is nowhere in sight, United Airlines, which designed the devices in-house in 2002, has continued to develop and install them on its fleet voluntarily, a move Duquette says the FAA fully supports.
Meanwhile, in 2007, Northwest (now Delta) began a one-year test program of the barriers on the airline's 747s. But after receiving negative feedback from crews, the airline decided not to move forward with widespread installation. According to Wolfgang Koch, a Northwest pilot at the time, the barriers created noise in pilots' sleeping quarters and made meal and beverage service to the cockpit difficult, as flight attendants were expected to close the barrier while their hands were full. Additionally, the airline estimated that the cost of the barrier would be closer to $100,000 over the life of the airplane.
As a result, Northwest decided not to move forward with the barriers. But Koch maintains that while that particular design wasn't ideal for the 747, the value of the device was clear.
"Some things are feel-good products and other things are substantial products. A secondary barrier is a substantial product," he said, adding that he believes Northwest gave up on the devices too quickly.
In the meantime, U.S. Rep. Steve Israel (D-NY), a longtime advocate of secondary barriers, reintroduced a bill in April calling for mandatory installation of the devices on commercial aircraft.