Very nice to think of a Sky Marshall sitting up the front with a uniform and a double barrel. My first thought was one fast acting poison blow dart and he is out of the picture.
And letting ex-cops (or current ones) travel armed? How do you ensure that they are not the bad fellas in disguise?
If you travel El-Al, you won't know who is security until you try some funny business- then you'll wish you hadn't.
Min of two ex-SAS types (that's Special Services- thanks ex-Sim, i had envisioned a large pair of cutting scissors!) trained to operate as a team in an acft cabin. It may be a good "after-Service" job for them, and we know we are getting trained operators who know how to deal swiftly and efficiently with a situation.
It keeps the element of surprise with the good guys.