A levels will help you get noticed in the job market and will open up opportunities at the entry level that you might otherwise not be eligible for. However, they're not much of a backup in life unless of course you lose your medical you are able to go to university mid-career to change direction.
If you get into aviation and land a job, do your A-levels part time if you have to at an adult college. Education in NEVER a waste. I remember doing all sorts of stuff at school and university and it really does broaden your horizons and make you a bit more intellectually agile. IMHO.