The first indication that something was amiss on Wizz Air Flight W9 4452 from Tel Aviv to London Monday was a hulking passenger who kept walking back and forth the entire length of the airplane, from the cockpit to the rear emergency exit and then back again. The plane’s engineer recalled: “I saw him going up and down, maybe looking for weak points on the aircraft… checking seat numbers… It was a very scary situation.” It got a lot scarier. Repeatedly screaming “Allahu akbar,” the suspicious passenger punched a crew member and tried to open an emergency exit door, which...