Now there's an avenue to explore.
No way to get into the cabin. The cockpit is completely separate from the cabin. The cockpit crew has its own door to get in and out, its own air supply, and its own toilet in there. And its own food cabinet and microwave. Plus cameras and mikes so they know what's going on back there.
And why stop at just one partition? We could separate the passenger area into noncommunicating sections, so a given knife-wielding maniac can only menace a fraction of the passengers. That reduces the risks, and cuts down the amount of gas we have to use. But it won't scale down well to anything less than a jumbo. Remember, each section needs its own toilets and stewardess and kitchen thingy.
We'd have to redesign the terminals a bit, though. More than one ramp per plane.
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