If the air has a net increase in downward momentum, how is
momentum conserved.
...by the air's eventual collision with the earth.
How is it conserved at the air/airplane collison?

(sorry, should have added this to the prevous post)

It is conserved because the wing gets pushed (back) up when the air
molecule gets pushed down.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.