Devils advocate,...sky marhsals make some sense, but only if we assume all the would-be hijackers get up at one time and reveal themselves.
What happens when all but one or two of the hijackers gets up, so they can see who the sky marhsal is. All that one or two have to do is wait for the marshal to turn his back and boom.
Ok,..the hijackers now have the passenger cabin undr control. Now to the pilots unbreachable door.
They tell the pilot to open the door or they will start executing all members in the passenger cabin.
So the pilot maydays the situation in and lands. Probably a best case scenario, but by that time most of the passengers will have been executed.
The plane is safe, the pilots and engineers are safe, and if the intention of the terrorists were to run into a building, that event has been stopped.
Sigh,..either way all the passengers and most of the flight crew are dead.
Deterrents are meant to keep sane people from trying something stupid. The insane terrorist is not going to be hampered by what we are suggesting.
The public outcry from all or most of the passengers being murdered because the pilot did not open the door would be very high. We would all specualte what the intention of the terrorist(s) were, and possibly lambast the pilots for not allowing the plane to be taken to save the lives of the ones murdered.
I have said it before and I will say it again. You cannot stop terrorism at the gate, it has to be stopped long before then.
Better security measures at airports is a good start. D/FW airport has enough security wholes to drive a truck of dynamite through.
The exits to the baggage area can easliy allow entry from the baggage area. There is no security at the those revolving doors.
At the entrance to the terminals, where you are supposed to be scanned, there are walkaround paths, intended for exits, but again, all you have to do is have one person distract the scan folks at the belts and anyone can walk right on through.
The items it takes to make a small, crude bomb can be carried onboard, without any trouble whatsoever.
You don't stop a child from being harmed on a defective playground toy by putting a band-aid on the wound each time he gets hurt. You remove or repair the toy that is causing the injury.
I am not stating we should not do what has been suggested. I think it is a start. But for any security measure to be effective, the whole path a passenger takes to get to the plane needs to be reviewed and look for ways to improve security.
Some added suggestions:
1) Immediately stop allowing carryons, except those required for medical purposes.
2) Secure entrance and exits in the airports better. This requires a wide range of ways and personnel to be looked into.
3) Cameras in the passenger cabin to allow the pilots to see what is going on.
4) Chemical scanners at the airport entrance. Metal detectors cannot detect plastic explosive.
5) Credential security for airline employees need to be completely rethought.
6) Collision detection could be implemented to have a plane circumvent the pilot to avoid collisions.
I am sure there are more. It is all about money. How much will it cost? How much more would you spend on an airline ticket? How long will it take to implement? How much to support it?
Anyway,..just some thoughts.