I agree with what Madman says. Much more can be done besides putting a gun on a plane. There are many disarming techniques that are fast and effective. Unless the pilot is a navy seal he would lose the gun. As much as the terrorists train for an event if they knew a gun was on the plane they would work it into the plan and it would be theirs. I carry a gun everyday and am a master firearms instructor but still would not want to have to place a bullet center mass of a terrorist in a plane with upwards of 200 people yelling and screaming.

The problem lies on the ground plain and simple. Secure the doors to the cabin profile the people who actually commit the crimes against us. A friend of mine just went to Germany and back. She is 501 100 pounds white female. She was searched both times she went through the gate coming and going. They said it was random. It is nuts.