I have been in the cockpit on a couple of take offs and landings in the last 10 years - it still happens - and of course it helps if you fly enough and start knowing crews. The captain has a fair amount of authority - there are some specific rules, for example in LHR (maybe all UK airports - don't know) - pax are not allowed in the cockpit for take off - but the same captain who told me that allowed me to be in the jump seat landing at a different airport. The flight crew is supposed to give you a "sterile cockpit" briefing. My first went something like this: "in the unlikely event something goes wrong, just stay quietly in your seat and let us work. You'll notice if something goes wrong - and if we start screaming, you can scream too - it won't be long then"