# 200 Proof: Airplanes Fly Parallel to Earth

15) If the Earth were truly a sphere 25,000 miles in circumference, airplane pilots would have to constantly correct their altitudes downwards so as to not fly straight off into “outer space;” a pilot wishing to simply maintain their altitude at a typical cruising speed of 500 mph, would have to constantly dip their nose downwards and descend 2,777 feet (over half a mile) every minute! Otherwise, without compensation, in one hour’s time the pilot would find themselves 31.5 miles higher than expected.

This is quite a silly concept to me. Remember that gravity is a force that acts on every object perpendicular to the surface of Earth. Please see my discussion on gravity for more detailed discussion.

Essentially, there are two issues. First, if a airplane is moving with a certain velocity forward and no additional lift; gravity will change the direction of velocity:

The problem with the author’s supposition is that too much energy would be required. Energy is required to move away from the Earth. Elevation is determined by position from the center of ball Earth, not where an object starts. If a plane noses down continually, it will crash into the ground.