Why does the A300 start without flaps (and i think even without slats)?

Answer 1

They aren't required to start the engines...If that's what you mean. If it isn't......What DO you mean?

Answer 2

All civil aircraft start with the wings clean because they are left that way when they are shut down. About the only aircraft I know that don't are Panavia Tornados after they have been on ground power, they shut down with everything extended or the hydraulic system ends up under full. Civil aircraft don't tend to run their hydraulics off external systems.