Airports share a number of variables with (rail) stations. The common variables are documented on a separate page
For other 80+x variables confer the TTD station structure. Note that you have to subtract 0x10 from the offsets there, or else the facility bit mask and construction date would not be accessible; instead you lose access to variables 00..0F which are meaningless anyway.
WARNING: Please do not use variables 8C..EB directly. The meaning of these variables changes if the newcargos switch is on. Use the variables 60..64 instead (common stations variables). Those always work correctly.
Airport layout (40)
This variable returns the layout number of the airport