An intruder was killed on a Denver runway after exploiting a security gap at one of the nation’s busiest airports.

Denver airport workers initially missed a security breach by a man who scaled an 8-foot perimeter fence and crossed a runway where he was hit and killed by a plane with 231 people on board.

Newer airport screening machines that operate like medical CT scanners are better at spotting liquid explosives, but many airports still lack that expensive equipment.

What is going on with aviation security.