Hi,

I would go with

1) Number of people in the world 7.5B

2) Segment them into (non flyers ~85%, occasional flyers 14%, frequent flyers 1%)

3) Multiply with number of flights (no flyers, occasional flyers 4, freqeunt flyers 10)

4) Multiply with hours per flight (5 hours)

5) Divide by hours per year (365 *24= 8760)

6) Multiply with share of flight time that you are actually not in the air (i.e. on the runway) - let's say half an hour out of 5 - so multiply with (4.5/5)

So the the whole equation looks like:

7,5 * (0,14*4*4/8760+0,01*10*4/8760) * (4.5/5) = 2,542,808-> ~2.5 Million people in the air right now.

You will note that it is quite hard to come up with very accurate estimates in 2) 3) and 4) but probably easier than trying to estimate number of airports and number of flights per airport.

Hope this helps.

John

(editiert)