Instead of trying to build a carbon emission estimate from the bottom up, which is fraught with missing data and uncertainty, why not approach this problem top down? Rather than inputting origin and destination airports, worrying about load factors, radiative forcing, seating class, aircraft models, holding patterns, what if we just average it all out?
Within a few minutes of googling you can find these figures for air travel in 2018:
Normalising: 918E9 kg CO2 / 4.3E9 passengers = 213 kg CO2 / passenger
This is an extremely reasonable sounding result. The atmosfair calculator suggests that a one way economy class flight ORD-SFO generates 211 kg CO2 emissions (accessed 2019-10-29). Of course, some flights will be shorter and some longer, but some will be empty and some full, some will use brand new planes with next generation engines and some planes will be decades old, and all of this information is usually missing from the emission calculation. Without going into serious detail, it’s pretty hard to estimate emissions significantly different from this average value.
Every time you get on a plane, you are responsible for 213 kg CO2 emissions.