How many aeroplanes do airlines use?

The airline will add two more A320s, to be based at Avalon, to its fleet of nine aircraft currently operating in Australia.

via theage.com.au

I’d never considered this question before. How many planes does it take to run an airline with a reasonable reach across (mostly Eastern) Australia?

Nine.

To me, someone who knows very little about the airline industry, that seems awfully small. There doesn’t seem to be much margin for error there - if one of the planes is defective, do they have a “spare” they can fly in to solve the problem? Can they afford a spare, given their rock-bottom fares?

Nine planes, soon to be 11. I’m sure similar numbers are available for other airlines, but I’m not enough of a planespotter to care. Idly interesting. Isn’t that what the Internet is for?