You simply can't make money in this game with 19 pax planes.
The routes will show profitable, but in reality they are not. This is because overhead costs aren't displayed on your profit figures, only the direct costs of lease/labor/fuel. All the overhead of all the salaries of your employees outside of the Pilot/Crew aren't figured in. Nor are the fixed maintenance costs. And since this game requires the same number of overhead employees whether you're opening a route for 747s, or a route for 9 pax Cessnas, you simply can't do it. You can't make enough money with 19 pax to pay the salary of all the other personnel you had to hire to run that route -- not unless it's a short route and you can run it 10 times a day or something. Even that's not a big help since some overhead personnel are hired based on how many flights a day you operate.
Throw in the fact that these planes are running at 50% occupancy and there's no way you can make enough money moving 8 people to make a net profit.