Hey,
If you do a search you'll find LOADS of info on this which is really helpfull.
I'm 18 and I have 4 weeks left doing A-Level, and from my experience when I asked the same question I found this:
A-Levels aren't important to get an airline job. However, if you wanna be sposored by say BA for example, their criteria ask for two or more A Levels. So if you're looking to get sponsored then its a good idea to have the qualifications.
Also, from common sense I would take A Levels. There's thousands of people who want the same job as you, so there's a high chance of not getting that job. In which case you'll need qualifications to fall back on, think of them as a safety net.
Having A Levels will make you stand out from the other CVs aswell, and A levels will allow you to move onto university which again makes you stand out from the crowd and it gives u a more secure safety net.
But all in all, DO A LEVELS THAT YOU ENJOY - Dont do maths because BA wants maths etc.
You'll find A levels hell if you're not enjoying the subjects, I did physics for three weeks!!
Enjoy, good luck and I hope this helps!
Ian