The fact that your CI is 30 suggests marketing might be killing you.
As Schro said, small planes aren't the easiest to run, and your not in the greatest airport for it either. Curfew hurts, flying less means the same overhead but less revenue. There aren't many really short routes, and the available profit on small & slow planes starts to drop quickly with distance.
It's doable, but margins are going to be pretty tight. Good way to learn though, fiddle with price, marketing, etc, see what happens. Have a look at profit/hr for a route, which is explained in the threads Schro linked to.
I've also just started take 3 of a small (& medium) airline experiment. London City just opened, so I just joined there. Will see how big I can get with just those small & medium planes allowed into the place.