Horizontal stabilizers and elevators keep a plane flying straight/level.
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Jets flying level/straight would be a fair test for a curved earth.
Elevators would have to be adjusted to follow the curve and not adjusting them would keep the plane flying straight. The difference between a plane climbing to a higher elevation and having a curved earth drop away from it is if the elevators were adjusted or not.
You all know this anyway, so without a doubt, planes favor a flat earth.
What I would say in public (small group or person to person) would be pretty much what I say here, if the topic comes up. The existence of God as the personal Trinity is always the main topic, evolution is second to that. The rules of rational thought are the means of proving God's existence and his nature. The rules of rational thought prove creation and refute evolution. Don't be upset with me for wanting a rational cosmology that does not violate these rules. This is mainly personal for me, not a public matter and I'm not ashamed to question this.
--Dave