Those expensive new doors are suppose to prevent that, are they not?
I go back to my human shield example. First guy comes in and lunges on the pilot with the gun...the others storm in and kill the crew members. They now also have a gun to take care of other people that may try to rush the cockpit to take the plane back (like what may have occurred on the United 757).
The only real way to secure the cockpit would be to have a secondary cockpit entrance from the outside only. Similar to another cargo door on the bottom of the plane, it would simply be a set of stairs that allows the crew to enter the plane and go directly up into the flight deck through an isolated compartment. Only opening to the cabin could be through a small door to slide meals to the crews. You get the idea...far more expensive, and current planes can't be retrofitted...but with the right layout - could work quite well.
dfw79,
I agree with the last part of your post, especially the part about being expensive. Therefore, that's just not going to happen. As far as your human shield theory, I think you need to become a little more familiar with aircraft and use some common sense. First of all, the doorway to the cockpit is very narrow. Only one at a time can come through. It acts like a funnel and would make them easier to shoot. On the MD-80, the plane that I am currently assigned to, the jump-seat can be lowered (I do it all of the time) to block direct access to the cockpit. To get in you would have to climb over the seat and that would give me even more time. At this point, the bad guy would be 2 or 3 feet from the end of a gun. One shot to the the head will send him on his way to collect his just reward. Now you have a narrow door, blocked by a jump-seat with a dead guy lying over it. The next guy to try to come in will have an even tougher time getting through that narrow door and climbing over his dead companion. After he's dead, his body will add to the already tight space and make it even more difficult. Need I continue? I hope you get the picture.
Now let's take a look at what you want. The bad guy gets in. I turn and look at him and wish I had my gun because even at 6'3" and 225 lbs I am in a very bad position to fight anyone. Especially a trained terrorist. Shortly thereafter, we are all dead.
Given the choice between the two, I think I like my scenario better. At least I (and everyone else in the plane) have a fighting chance.