If you've been on steroids for a couple of months a) it's bad and b) you need medical advice about coming off them. Please don't just stop, speaking from experience, it's agony if you do.
You need to consult your DR /consultant about what you you should do.
A couple f years ago, I had to delay a three week holiday by a week for the same reason.
At the mo!ent, I'm on my second five days course of steroids and second seven day course of antibiotics. It's a bugger.
BUt, better safe than sorry. Altitude can affect your btrathimg, let alone walking up the stairs to the aircraft. I hated putting my much needed holiday back, but if that what it taes, that's what is going to happen.
Exacerbation on a plane? You may die, you .do realise that, don't you?