Click or tap on the ad to reveal the answer.
How to guess it?
Just like the February 2000 advertisement, the font was an important clue. Although this airline stopped using this font for a couple of years, it is easily recognizable.Also, you could take a while looking on the Internet to find out what was the first U.S. airline to offer nothing but no smoking flights worldwide. At the time, it was quite recent but today, all U.S. domestic flights are non-smoking and the trend is scattering on airlines worldwide.
Finally (and this is quite obvious), everyone who saw this ad or one of its variants some time during the last 6 years recognized the airline immediately!