LGSK has a relatively short runway of approximately 5000 meters.
After loading my passengers, I tried to do a takeoff calculation using the PMDG tablet which promptly threw an error of the aircraft being overweight. I then tried to do a takeoff calculation using simbrief which resulted in the following image:
Hi, this is not a bug, it’s just not something that is currently implemented. SimBrief doesn’t prevent planning to/from an airport or runway that is too short.
You can however run preliminary performance calculations while planning your flight by clicking the provided icons above the runway selection dropdowns: