Airport security screeners reportedly missed a vast majority of concealed guns and bombs in a recent test at one of the busiest airports in the country, and one expert tells ABC News there’s a simple explanation: Not enough people working the checkpoints. The Newark Star-Ledger reports 20 out of 22 weapons got past screeners at Newark Liberty International Airport checkpoints. ABC News aviation consultant John Nance says that while screening has improved since 9/11, "One of the reasons it’s not perfect is that they haven’t given us enough people." THE BLOTTER RECOMMENDS Seized at the Airport, Sold Online: Bureaucrats Get Creative Dress Code Dropped for Undercover Air Marshals Click Here to Ask Brian Ross a Question He says training is also a problem. "They failed these tests, and that means more needs to be done with training." The airport’s Federal Security Director Mark Hatfield Jr. agrees "training is the path to improved performance," and he told the Star-Ledger, "We can do better." But training has been a consistent problem in the past. The Government Accountability Office (GAO) says covert tests — like the one in Newark, where weapons are hidden to test airport screeners — have shown "weaknesses and vulnerabilities continue to exist" at airports of all sizes. A GAO report in April stated that part of the problem was "attracting, hiring and retaining" an adequate pool of screeners and that staffing shortages make it difficult for screeners to attend mandatory training. It also said screeners at some airports have trouble using the TSA’s online training resources because they lack high-speed Internet connections. TSA officials would not comment on the recent Newark Airport test results, but a spokeswoman told the Star-Ledger that concealed weapons tests have a "high level of difficulty" and that TSA uses those results "to adapt and improve upon our screening protocols and training regimens." TSA has been phasing in new explosive detection systems, which scan bags automatically and reduce the potential for human error, but the upgrade is projected to cost $22.4 billion over 20 years, and at the current rate, the new systems won’t be fully operational until 2024. Airport screening isn’t the only area where aviation security has run into problems. Read about trouble with the Federal Air Marshal program.