When I want to speak of a woman who serves food and drinks to passengers on a plane, should I use 'air hostess' or 'stewardess'? What's the difference? And when I take a plane, how should I address her?
In the US at least, both have fallen out of favor in recent years for a couple of reasons: because there are more men working in the field than there used to be, and because of a general trend towards less gender-specific occupation titles. The more widespread term now is flight attendant, for both men and women.
They are called flight attendants, and you must not assume it will be a woman.
Other terms, such as “air host/hostess” and “steward/stewardess” are quite dated. I would advise against using them. And if you were to use them to address a flight attendant, you will be lucky if you get any service at all, because of the offense they would cause.
Furthermore, since it is generally considered pretty rude to address a person by their occupation—many servers in restaurants, for example, hate being called “waiter” or “waitress”—I would advise addressing a flight attendant with “sir” or “ma'am” if you need to use an address at all. “Excuse me” should be sufficient to get a flight attendant’s attention when necessary.
I agree with phenry's answer (and those of the others) about both terms being offensive of late, and obsolete as well. But given the fact that the question was asked from China, I thought I might as well put forth my opinion.
I believe there was a major difference between a stewardess and an air hostess.
I remember being taught that a stewardess is the lady who is in charge of preparing and distributing food in the aeroplane.
An air hostess on the other hand is the lady who is in-charge of welcoming you onto the aircraft, providing you with your pillows and blankets, in charge of your safety (remember the original air hostess served as medical nurses abroad international flights) and any other enquiries you might have.
However, like everyone pointed out, this is pretty obsolete now (as has the system of unwed airhostess) and everyone is known as a flight attendant or cabin crew nowadays. And they usually end up taking care of both the activities mentioned above.
You could always call her a "waitress in the sky".
It depends who is doing the speaking. If you're writing a story, and it's a lecherous salesman type, you might use "stew".
I usually use "Miss" to address "younger" female flight attendants, and avoid the issue with the others "Excuse me, ... ".
A woman who serves food and drinks on a plane (as in the original question) is probably:
A drunken air hostess
However, a woman who serves food and drink on a plane is called simply an air hostess. You need not be overly concerned about her title — I would suggest that you address her as “Miss” or “Madam” depending on her age.