Last fall, as he had done hundreds of times, Iranian-American businessman Farid Seif passed through security at a Houston airport and boarded an international flight.
He didn't realize he had forgotten to remove the loaded snub nose "baby" Glock pistol from his computer bag. But TSA officers never noticed as his bag glided along the belt and was x-rayed. When he got to his hotel after the three-hour flight, he was shocked to discover the gun traveled unnoticed from Houston.
"It's just impossible to miss it, you know. I mean, this is not a small gun," Seif told ABC News. "How can you miss it? You cannot miss it."
But the TSA did miss it, and despite what most people believe about the painstaking effort to screen airline passengers and their luggage before they enter the terminal, it was not that unusual.
Experts tell ABC News that every year since the September 11 terror attacks, federal agencies have conducted random, covert "red team tests," where undercover agents try to see just how much they can get past security checks at major U.S. airports. And while the Department of Homeland Security closely guards the results as classified, those that have leaked in media reports have been shocking.
According to one report, undercover TSA agents testing security at a Newark airport terminal on one day in 2006 found that TSA screeners failed to detect concealed bombs and guns 20 out of 22 times. A 2007 government audit leaked to USA Today revealed that undercover agents were successful slipping simulated explosives and bomb parts through Los Angeles's LAX airport in 50 out of 70 attempts, and at Chicago's O'Hare airport agents made 75 attempts and succeeded in getting through undetected 45 times.
Despite the results, there is no sign that the numbers have changed as the screeners have been tested year after year, former Department of Homeland Security Inspector General Clark Kent Ervin told ABC News.
"Those reports were classified but it's sufficing to say that reports, both classified and unclassified, are concerning. Too often guns and knives and fake explosives get through the checkpoint," Ervin said. "And what is particularly concerning is that nine times out of 10 the checkpoint is the most critical layer of aviation security."
Ervin said a combination of factors is likely to blame for the persistent failures on the part of screeners. Low pay, poor training, and the monotony involved in watching bags pass through x-ray machines are a recipe for trouble, Ervin said.
"To be fair to screeners, it's very difficult work," he said. "After so many hours of seeing things that are innocuous, there's really a limit for the human brain to process something anomalous."
Last month, TSA Chief John Pistole told ABC News that the poor performance during undercover tests helped convince him that airport screening needed to get that much tougher -- and a desire to do better helped give rise to the controversial new regimen that includes enhanced pat-downs and back-scatter machines that can see beneath a traveler's clothing.