I seems the Transportation Security Administration (TSA) are unable to detect loaded firearms:
After reports of two loaded guns making it past airport screeners and on to passenger flights this week, one congressman says “hundreds” of prohibited items get past screeners every day, a situation he calls “intolerable.”
In one of the incidents last week, Transportation Security Administration screeners allowed a New Orleans Hornets executive to board a plane from New Orleans to Newark, N.J., with a loaded handgun in his baggage.
[…]
Just one day earlier in Orlando, TSA officers missed another loaded gun. This time, a firefighter had mistakenly left the gun in her purse and carried it right through security screening and on to her plane. The firefighter realized on her own what had happened and alerted authorities.
This isn’t an entirely bad things mind you. If would be hijackers knew that travelers could be armed they would probably be less inclined to make an attempt to take the plane. Unfortunately this news is being treated almost exclusively as a bad thing because people who lack imaginations don’t see the upside of armed travelers.