Do planes fly in a straight line or follow the curvature of the Earth?
Do planes fly in straight lines or follow the curvature of the Earth below?
When I began to learn how to fly, during my first lesson, my instructor told me to maintain a ‘straight and level’ flight at 3000 feet. Heck, I was struggling to perform this exercise not knowing whether I was actually flying on a flat Earth or on a curved one.
Ajay Rim who asks this question is probably thinking out of the box. He wonders whether the plane would maintain a straight line as if the Earth is flat or that it would follow the curvature of the Earth.
Well, the plane would definitely fly into Outer Space if indeed it was flying in a three-dimensional straight line.
In reality, this is not possible because a plane’s engines can only operate at lower altitudes in the atmosphere where there is oxygen and air to keep the engines running and plane flying. It is helpless in Outer Space because there is no air to produce lift and propulsion.
If I were to fly from Stockholm to Kuala Lumpur on a Boeing 777 at 39,000 feet in the cruise, it would not end up at a higher altitude than at the start. Hypothetically, if the plane did fly on a straight line, it would start to “fly” into Outer Space because it would fly along a tangent to the Earth’s curved surface.
Therefore, the Boeing 777 does not fly in a straight line but follows the curvature of the Earth. In fact, it continues to descend imperceptibly at 8 inches per mile squared.
This is achieved by the autopilot or manually by maintaining the planned altitude of 39,000 feet (or even higher when the plane becomes lighter) all the way to Kuala Lumpur.
The plane maintains 39,000 feet because it is the atmospheric pressure that determines this altitude. During the cruise, the autopilot will hold this altitude by constantly moving very subtly the flight controls in order to maintain the altitude.
So, whether the pilot or the autopilot is flying the airliner, it is the altitude on the altimeter that ensures the plane is following the curvature of the Earth strictly.
This is analogous to, say an ocean liner sailing across the Atlantic Ocean from New York to Southampton in England. No matter where you are on the surface of the ocean, you are at the same distance above the center of the Earth.
For navigation purposes, pilots do take into account the curvature of the Earth. They fly by what is called a Great Circle route. It is just like how a crow flies in a straight line. It cuts corners to get to your destination in the fastest time and with the least fuel burnt.
To answer to Ajay Rim’s question, a plane will always maintain a constant height and follows the curvature of the Earth when it flies at a particular level. Thanks to gravity, the altimeter and the autopilot or the aviator if he was flying the plane manually.
View a video explaining the Curvature of Earth – 8 inches per square mile here