I'm not sure aircraft weight in flight increases atmospheric pressure (weight) on the ground. But using the analogy of the weight of people in a building increasing the pressure the total building + people puts on the ground...
1) Only aircraft in flight at a given instant count. That would be on the order of 10000 aircraft at any one instant. Could range from 8000 to 12000 depending on time of day (and where "day" is at any instant - U.S.? EU/Africa? Asia?).
2) Weight of those aircraft - C150 to A380? Let's take the 739ER as a reasonable average: MTOW = 71350 kg
x 10000 = 713500000 kg or 7.135 x 10ˆ8 kg
3) Weight of the atmosphere = 5.1 x 10ˆ18 kg
4) aircraft weight adds a bit over one 10-billionth (or ten 1000-millionths) to the total.
5) In millibars, average atmospheric pressure with no planes flying = 1013.25 millibars
- with planes included: 1013.25000017418 millibars
A microscopic difference, in other words....
(Assumptions and math open to criticism).
Last edited by pattern_is_full; 3rd Sep 2017 at 12:36.
Reason: spelling