Use the weight of fuel needed to operate the route with an assumption of average weight added per passenger both added to a planes operating empty weight to just make an assumption as to what the aircrafts weight would be and then base the % difference between that and MTOW as the % difference in runway length needed - making adjustments obviously if necessary.
It would be a lot more complex than anything we've seen with CA, but it would be the most realistic and would only require you to find one extra number (an OEW) for each airplane to make it work.
It would be a lot more complex than anything we've seen with CA, but it would be the most realistic and would only require you to find one extra number (an OEW) for each airplane to make it work.