Just as a reminder. As the calculations have been tuned you will see results that are not similar to previous games, if you've played them.
The company & route image variables are more dominant now, and so is the seat config effect.
In short - when you start your airline the company is unknown and all the routes are new and unknown to public. This means that you CAN NOT attract full planes right from the start unless your pricing is very low. So with near-deafult pricing you can except some 30-50% load factors, depending a bit on how large route you operate.
To cope with this (see manual) there are three main ways .. 1) let the time go by & fly the route, this raises the route image (awareness). 2) marketing (raises company image, and route images), 3) lower prices (lowering prices will attract more people). If you lower prices, remember to pump them up again then you're company and route are more known.
The seat config effects have also been improved. So flying longhaulers with high density seating doesn't give very good results anymore.