Loaded technically isn't a problem, made ready is! That is when the round is in the chamber. loaded simply means the magazine is in it's housing. But still it shouldn't be allowed. That said the myriad of CCTV that exists in the bag lines and sort system and loading bays makes it hard for employees to tamper. Plus the fact that PECs keep a track of bags positions on the belt. If a bag is moved or 'fondled' the system rejects the bag and sends it back to square one for level one screening.