I havent made it to the airlines (yet) but in my current field we are TDY about 1-2 weeks out of the month, so in a way it's similar.
You have to accept that while you're on the road, you are going to lose gains, but the key is to stay focused and work to maintain what you built up while at home, or at least to limit the gains lost on the road. To do this, I make sure that I adjust my caloric intake accordingly. This is essential, because if you eat like you just got done squatting 405 or deadlifting 495 when you really didn't do anything that day, you're just going to balloon up. It's really easy to get caught up in the whole I'm away from home mentality, especially after a long day and when your co-workers suck you into Outback or Olive Garden. You just have to resist and stay true to your goals.
For this, meal prep helps a lot. If you can get a fridge and microwave in your room, then you can go to Walmart and buy some macro-appropriate food to stage. If you know in advance that you are going to have a fridge and a way to heat up your food, you could bring some chicken breast pre-made with you in a small cooler on ice for the week, along with broccoli and some rice. Bring a small rice cooker or Crock pot with you to make fresh sides. Don't forget protein power. I take mine out of the tub and put them into gallon freezer bags to save space. It kind of looks like cocaine, but I haven't had a problem yet.
As far as the workouts, this part can be easy to skip. I've been tired after a 12 hour day, but you have to get in there to work out. Find a national gym chain, like LA Fitness or 24 Hour and join that if you find yourself in cities. If you're really serious, and can afford it, why not have multiple gum memberships to make sure that you always can get a workout in? If you're unfortunate and have to fly into small areas where there are no gym chains, it sucks, but you should still pony up for the temp membership to whatever moms and pops gym they have in the area. The key is consistency. It all pays off in the end, just don't quit.