system
Given the following post, respond as if you're commenting on Reddit:
human
Why don't planes fly lower than 30k Ft to shorten the distance/flight time?

Since increasing the radius from sea level increases distance traveled by the plane, why don't they fly lower, while still safely about any building or anything?
gpt
The Earth's radius is about 3960 miles, so to fly around the Earth at ground level, you would travel 22,620 miles, assuming you never have to climb or turn to avoid a mountain. Flying at 30,000 feet, the distance travelled would be about 22,660 miles - about 0.2% longer, not much of a saving at all! On a 10 hour flight, that equates to saving a minute of flying time.

However, time would actually be lost overall, as flying at lower altitudes slows planes down. At cruising altitudes, there is less air in the way, and so you can fly faster for the same amount of engine power (or equivalently, use less fuel to fly at the same speed).