I am a 32 year old with CF and have done a lot of traveling by plane. I had only one experience when it was difficult to breath. Check the air carrier you chose on their policy about the percent of recycled air during flight.
Airlines save a bundle in recycling air.
Ask to change seats if you suspect that you are sitting next to someone with a cold. The airline usually has a department they can refer you to answer medical questions. After innumerable flights overseas, this most recent one was the first smoke-free flight I've been on.