All the respondents are correct, but there's more to the story. At the present time, "flight attendant" is far more prevalent than either of the other options, "air steward" or "air hostess." The phrase "air stewardess" was never popular in English. Nevertheless, at one time, "stewardess" was the predominant term for women employed in that position. Before the 1970s, men employed in service aboard passenger airlines were known as "pursers." I don't believe that refering to them as "air stewards" ever was commonplace.
http://airandspace.si.edu/exhibitio...e/pan-am-clippers/what-was-it-like-to-fly.cfm "Four pursers looked after passenger needs and converted the lounge into a dining room at mealtime."
If you view this
Google ngram comparison, you can see that it was in 1975 that "flight attendant" became more common than "air hostess," and you can also see that "air hostess" has always been more common than "air stewardess."
"Air stewardess" would have been viewed as redundant. "Stewardess" was pretty much only used in the context of on-airplane flight service. So if we
change the ngram to omit the "air" before "stewardess," you can see that the ascendancy of "flight attendant" over "stewardess" is much less extreme and much more recent.
I would say from this evidence that "stewardess" is still in fairly common use, but it is marked as old fashioned and, especially, inappropriate for business use, where "flight attendant" is the more standard term.
https://airandspace.si.edu/exhibitions/america-by-air/online/jetage/jetage11.cfm "Reflecting the social changes of the 1960s and '70s, the term "stewardess" evolved into gender-neutral 'flight attendant.' Conservative uniform styles reappeared due to new laws that prohibited discrimination in hiring based on age, appearance, and gender. Men now returned to the profession as well."