How airplanes would fly on earth?

Hello,

Sorry for the Brazilian English, I am busy and no time to practice. 

I became interested in the idea and came a doubt...

If the earth is flat, gravity would be the acceleration of itself in relation to space at 10m / sē, how airplanes would fly on earth?

Hello,

Sorry for the Brazilian English, I am busy and no time to practice. 

I became interested in the idea and came a doubt...

If the earth is flat, gravity would be the acceleration of itself in relation to space at 10m / sē, how airplanes would fly on earth?

I'm not sure I understand the question.
The equivalence principle states that the two forces (UA and gravity) would be indistinguishable, and I see no reason lift would be diminished.

If the earth is flat, gravity would be the acceleration of itself in relation to space at 10m / sē, how airplanes would fly on earth?

Wings provide lift as air flows over them.  This lift is a force on the airframe of the aircraft.  F=ma.  If the acceleration is equal to 9.8m/s^2, then the airplane maintains altitude above the FE.