(0.7 + 0.3 * loadfactor)
This explains a lot of the balancing issues and why all routes need to be at 100% load factor. It needs re-balancing as a plane at 50% load is using only 15% less fuel, coupled with the random swings in passengers this is making the game a chore.
For dealing with the passenger swings, pay attention to the "Overall Quality" of the route. Route quality is determined by three factors:
- 30% based on the number of stars you assign (1 star gives 6 points, 5 starts gives 30 points)
- 50% based on your global service quality (100 global service quality gives 50 points)
- 20% based on airplane condition (a 100% condition airplane gives 20 points)
So at 40% autorenew you will naturally see the route quality drift downward across a 12 point band.
Each point of route quality is worth
about a 0.5% increase in price, within a certain range. If your route quality is too low for the type of route (domestic routes only really need you to be in the 30s, intercontinental want the 50s-60s) then you will actually take a more severe pricing penalty. If your route quality is too far above what passengers want for the type of route, it doesn't give any further advantage. (You can get about 25% increase in pricing power total from route quality, IIRC.)
So either you can pretty regularly fiddle downward your prices, OR you can leave money on the table and calibrate them for your lowest airplane condition. Or you could try something fancy to try to balance out planes (e.g. assign one new plane and one old plane to a route so that the
average condition stays in a narrower band).
This isn't the only source of randomness but it is the primary cause of "my route that was just fine earlier is now all jagged and gross", alongside new competition on the route showing up.