The arrest of an airline mechanic suspected of being sympathetic with terrorists and charged with sabotaging a jetliner has renewed fear about the “insider threat” to aviation security. Despite security upgrades since the hijacking terror attacks of 2001, breaches including a gun-running operation at the nation’s biggest airport illustrate the possibility that a well-placed airline or airport employee could bring down a plane. “Should people be worried? Hell, yeah,” says Doron Pely, a former aviation security consultant in Israel. “This doesn’t require a suicide bomber. It requires access to an airframe, an aircraft and motivation.” Several experts interviewed for this story said it would be difficult if not impossible to stop every determined criminal or terrorist. They said steps that might beef up defenses against an insider attack – such as requiring aviation workers to go through security checkpoints just like passengers – could add costs and slow down work that goes on at airports. While there have been several cases in recent years of insiders using their special access to board planes without going through security – in one case, even steal a plane – they haven’t harmed passengers, and there hasn’t been clamoring for tougher security. Under federal law, people applying to work in secure areas of an airport must pass a three-part vetting process run by the Transportation Security Administration – a criminal-records check, a “security threat assessment” that includes checking their names against a terrorism watch list, and proof that they are eligible to work in the United States. Abdul Alani, who was born in Iraq and became a US citizen in 1992, passed that test and got a job repairing planes for American Airlines. There were setbacks in his career – Alaska Airlines fired him in 2008 for shoddy work, something that American apparently didn’t know – but there was no criminal history, no other outward signs of problems.