Quite simply you cannot. It is widely stated you would need to be at a height of at least 40,000 ft to get even a hint of curvature if earth were round. Commercial aircraft are not allowed to fly this high. They are only allowed to fly just under this altitude. 36,000ft might be typical. In addition, the windows on commercial aircraft are small and heavily curved. Even if they flew high enough for a person to see curvature, it would still not be visible to passengers.
171) NASA claims there are upwards of 20,000 satellites floating around Earth’s upper-atmosphere sending us radio, television, GPS, and taking pictures of the planet. All these supposed satellite pictures, however, are admittedly “composite images, edited in photoshop!” They claim to receive “ribbons of imagery” from satellites which must then be spliced together to create composite images of the Earth, all of which are clearly CGI and not photographs. If Earth were truly a ball with 20,000 satellites orbiting, it would be a simple matter to mount a camera and take some real photographs. The fact that no real satellite photographs of the supposed ball Earth exist in favor of NASA’s “ribbons of composite CG imagery,” is further proof we are not being told the truth.

121) When you observe the Sun and Moon you see two equally-sized equidistant circles tracing similar paths at similar speeds around a flat, stationary Earth. The “experts” at NASA, however, claim your common sense every day experience is false on all counts! To begin with, they say the Earth is not flat but a big ball; not stationary but spinning around 19 miles per second; they say the Sun does not revolve around the Earth as it appears, but Earth revolves around the Sun; the Moon, on the other hand, does revolve around the Earth, though not East to West as it appears, rather West to East; and the Sun is actually 400 times larger than the Moon and 400 times farther away! You can clearly see they are the same size and distance, you can see the Earth is flat, you can feel the Earth is stationary, but according to the gospel of modern astronomy, you are wrong and a simpleton worthy of endless ridicule if you dare to trust your own eyes and experience.