I don't have exact numbers, but less common than the 70s and more common than today. Like I said, they peaked in the 60s and 70s. While the TSA didn't exist u

I don't have exact numbers, but less common than the 70s and more common than today. Like I said, they peaked in the 60s and 70s. While the TSA didn't exist until after 9/11, TSA style screenings were introduced in response to those hijackings. That was at least part of what caused the numbers to drop through the 70s, 80s, and 90s. That is why I'm not willing to completely dismiss those screenings as security theater. Sure, taking off our shoes is almost certainly meaningless from a security perspective. But walking through a metal detector and putting our bags through x-ray machines likely does help. Basically the screenings that still happen for people with TSA Precheck show what security practices are likely the most valuable.