On a recent KLM flight from Cape Town to Amsterdam via Johannesburg there was a crew change at Jo'burg. The cockpit door was left wide open and a number of us passengers, me included, wandered up to (but not inside) the cockpit to gawk at all the gadgets etc. Fascinating to this PPL, but I did wonder at the time how come no-one challenged us. We could easily have got inside had we so been inclined. A member of the ground crew pushed past us at one point to complete a check list in the cockpit but didn't seem bothered by us. Most of the one hour stop-over time we were the only occupants of the entire area!
Security risk?