They [airliners] would also have to be constantly climbing to keep from being caught by the earth while it is accelerating at 9.8 m/s.
Here's another scenario I have not seen addressed as yet. The earth accelerates upward. Do all objects associated with the earth, or in the vicinity of the earth, accelerate similarly? The sun, moon and planets which circle above the earth remain in place (save for the curious vertical variations in their orbits required to explain seasons, eclipses, etc.), relative to the earth, causing one to infer that they are under the influence of the same "unknown force".
Well, it's generally accepted by the Round Earthers here that UA is not the breaking point of this site's FE model(s).
1. Airplanes really do continuously "climb". They don't float.
2. Air is being accelerated just like we are because it and we are pressed against the earth.
3. There's no discernible difference for us between gravity and UA
4. As for celestial objects, it's not a real stretch to believe that UA affects them or doesn't affect them. I don't think anybody has gone so far as to create a model for how they actually move.
As ludicrous as UA seems, it doesn't break any rules. What are more egregious are things like:
1. The sun, moon, stars, ships, mountains, and buildings do not really appear to rise and set at the horizon. They simply fade or shrink.
2. The distances between any four trapezoidal remote world points are not known (admitting they are known would prove they cannot geometrically be represented on a flat figure).
3. Mountains can cast shadows on the underside of clouds from a sun 3000 miles above it all.
4. The time and location of equinox sunset all over the world are not known.