If you're planning to fly on American, Delta, or United, and carry a piece of luggage on board, better check the size. All three airlines have announced plans to reduce the acceptable maximum size to 22 inches long, 14 inches wide, 9 inches high.
JetBlue, Southwest, and other domestic carriers still permit bigger carry-ons up to most 24 inches long, 16 inches wide and 10 inches high.
Just before actually getting to the TSA agent's podium, a red-jacketed person (who I believe was hired by American Airlines as a subcontractor but not an actual employee) insisted that I put my suitcase in a bag sizer. Keep in mind that I was flying in business class, and that I've taken this same 21-inch four-wheeled suitcase all around the world on almost every major airline and quite a few not-so-major ones.
To make a long story short, it was rejected as "too big." What I didn't realize, because it's never been an issue before, is that American (as well as Delta and United) has updated their carry-on bag policies, including a 14-inch maximum width, and my Rimowa is 15 inches wide, as are many carry-ons. Even though it's an inch shorter than the 22-inch length limit, and an inch below the official 9-inch depth limit, back to check-in, I went. And the line was so long, I almost missed my flight. I was then told that this is a new "FAA regulation," a questionable claim given that not all airlines have the same allowances.