It's a numbers game and the terrorists have the initiative at every point. That's why active preventative measures won't be too effective. A silly toner cartridge from Yemen almost brought down planes over the US. Before it was underwear, shoes, boxknives.
It's always going to be something we haven't thought of because they have the ability to look for the weaknesses before they hit. The only way you have no weakness is to have a police state and even then, you'll fail.
It is a numbers game, and it's one that defensive measures are going to lose EVERY SINGLE TIME.
Screw locking the cockpit door. Stop designing planes with access between the cockpit and the cabin. Seperate the cabin with a wall and only allow access through a small window to the cabin.
Yes yes, all you anecdotal fools will go "OMG what happens when the pilot has a heart attack and the co-pilot an aneurism". Just shut up and go tell me the last time that happened, m'kay?
Next - US Marshals on more flights. Fire nearly every TSA screener and replace them with Martials.
Let's get something else straight. If I want to blow up a plane, I'm going to blow it up. That's the simple truth - learn to deal with it.
One could put a bomb with a cell phone trigger in the the luggage. What's that, you're going to jam cell phones? I'll put it on a digital watch as the timer. EMP pulse it before loading the luggage? I'll put a wind-up alarm clock on it. Enforce no luggage? I'll bring a small plastic pressure container with propane in it. Perhaps the size of a pill bottle. I'll release it by unscrewing the cap, then light a match and blow out the side of the plane.
Anyone who thinks they can be safe is an idiot. You can be stabbed in the back at the supermarket, shot in a driveby, accosted in your home, blown up on a plane, I could go on for ever. Those same idiots who think that someone just one more safety measure will make them safe are some of the jackwagons that are destroying this country and taking away our freedoms. Once they finally get to the point they feel safe, someone will drive a vehicle filled with aerosolled gasoline into a daycare and start the same cycle all over again.
You ARE NOT SAFE. You never will be. Now go the fuck away if you can't accept it, because it's the simple truth. Stop trying to take my freedom and liberty away because you're a scared little nancy boy (or girl) who wants mommy to come save them in the form of big government.