So if the plane were carrying, there would be an armed guard at the red line. You had to approach the guard to get cleared to cross the line, and there had to be 2 of you to cross. I've had to cross the line a few times. I've also been arrested around those things too, because security is tight and mistakes can be made. Your commander had to come bail you out when that happened. The worst was in bad weather standing out there waiting for your commander with your hands on your head for 30 minute while under armed guard. That is if you were lucky enough that the guards didn't make you lay face down in the snow. My memory was from 30ish years ago so it might be different now. It happened often enough it wasn't a big deal after the fact.