Hey Manni!
I’ve had issues with this as well. At first, my planes left with only 50-60% of the total number. A lot of the time, passengers get delayed due to badly designed passenger flow. And in my experience, it turned out that my airport design was not the most efficient. So, I made a few changes. Please refer the post mentioned below, and if possible, the whole thread. I was able to eliminate 95% of the delays (some delays are inevitable and that’s okay as airports face delays in real life as well) that occurred for me. Alpha 31 - Delays - #25 by ilios21 Also, remember to hire the best security officers as it will improve the efficiency of your security system.
After you’ve implemented these suggestions, do let us know if it works or if you still have problems. 