You don't need A levels to begin training to become an airline pilot - the very basic requirement is GCSEs. Having said that, you will no doubt need A levels if you apply for any of the "sponsorship" opportunities out there and the selectors may ask for science subjects. Having a degree may also make you more attractive on these schemes.
All the answers you need are in the posted link above - it might take a few days of reading to get through it though!