I've never successfully picked up a stewardess/flight attendant directly from on board any flights. And haven't really tried, because they are too "professionally polite". I would focus on women sitting next to me, if I got lucky with sitting next to a single and cute one, or when waiting in the terminal for the plane.
I've always met flight attendants accidentally on the train (coming from the airport), in clubs, or online. So it's always been a random surprise treat, versus any planning or targeted pickup on my part. However their schedules tend to be problematic for me, unless they are open-minded about sex and relationships. I've actually had better consistency and relationships with women that worked at the airport, but weren't flight attendants.
I'm with Sinapse on this one. In terms of appearance, most Asian airlines have at least decent looking and tall-ish women. Like when I flew on Korean Air, a few months back, I had no complaints. I didn't see the next Miss Universe in the group, but they were do-able and didn't hurt my eyes.
I was on an American Airlines flight a few years ago, and was treated to the fat-est flight attendant I have ever seen. The woman was so WIDE, that when she turned around between the aisles, she was hitting passengers with the side of her hips. Ridiculous. I was thinking there should be at least some type of weight limit or at least "width limit" for airline attendants for safety and health reasons.