Whether you get access to the flight deck is down to the CAA of that country, company policy and the Commander.
I think if you make yourself known to the FO or the Captain, they will be more than happy to answer any questions you have, I know I am more than happy to help, and quite enjoy it when people show an interest. It is such a shame that we cannot grant access to the flight deck anymore on British Reg aircraft, as it is great to share your enthusiasm with like minded people.
Dont be shy to express an interest, nine times out of ten you will find most guys or girls are willing to chat with you. Sometimes it is tricky with tight turn arounds but I always try to find the time
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