...and THEN add in factors such as scheduled maintenance and unscheduled maintenance. Only certain locations are equipped to perform certain maintenance. So, let's say an ultra-sound inspection of a wing spar has to be performed every 500 flight hours, and only LAX and MIA are equipped to perform that inspection, the scheduler needs to ensure that every 500 flight hours that plane's last flight of the day ends at LAX or MIA. But let's not forget, there's dozens of other schedulers who are also trying to get their planes inspected...and each base can only accomplish 2 inspections per night. Uh-oh...the ultra-sound equipment in MIA is due for it's annual calibration; it will be down for 2 days until the guy who's certified to do the calibration gets back from vacation..........

And that's just one inspection out of thousands.

It's a breath-takingly complex affair.