I find "Sir" is sufficient
Back in the real world I use first names with all of the crew and expect the crew to do likewise with me. And I regularly take a stroll back to the L/R4 doors to say hi on boarding and have a bit of banter before I get locked away in my box for 8 or 10 hours
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Possible cultural differences in the Far East and Middle East may dictate C/C having to use the term "Captain". I know that first Officers in a large Dubai based airline are known as 'an yoo's' as in "would you like a drink Captain..........? An yoo?" (whilst looking with disdain at the poor F/O)
