Understanding Flight Paths: Why Planes Fly Curves and Not Directly Over Mountains

When you imagine a direct path between two distant cities, such as Sydney and London, it seems logical to envision a straight line through the Earth's surface. However, the reality of air travel involves complex considerations that impact flight paths, often resulting in curved routes. We will explore why airplanes often fly in curves, especially when traveling over mountainous terrain. Additionally, we will discuss how some flights can indeed appear to follow a nearly straight line, albeit as a result of the Earth's curvature.

Why Do Airplanes Fly in Curves?

The most fundamental reason for curved flight paths is the shape of the Earth itself. When flying between two distant points on the planet's surface, the shortest distance (geodesic) is not a straight line, but a curve known as a great circle. This curve is the largest circle that can be drawn on a sphere, and the arc on such a circle that has the two points in question as end points is the geodesic, or "shortest distance," between the points.

Practical Considerations

Even though the term "shortest distance" might imply a straight path, airlines and pilots must navigate around practical constraints like altitude, air traffic control rules, and weather patterns. Typically, flights are conducted at higher altitudes, where air is thinner and easier to navigate, and where the curvature of the Earth is more noticeable. This means that the actual flight path may not appear as a straight line on a flat map.

Why Can’t Planes Go Directly Over Mountains?

Traveling over mountains or other elevated terrain poses significant challenges for airplanes. Several factors come into play here:

Fuel Consumption: Flying over mountains requires more fuel due to the increased altitude, reduced air density, and the need to maintain stable flight paths. This is why airlines prefer to take routes that offer the least resistance. Air Quality: The air at higher altitudes is thinner, making it harder for engines to maintain efficiency and speed. Air Turbulence: Mountaintops can create turbulent air patterns, making the flight uncomfortable and potentially hazardous.

However, it’s important to note that sometimes planes do fly directly over mountains. In such cases, the plane flies at an ample altitude where it can handle the turbulence and maintain a stable flight path. This is often seen in transcontinental flights where going around a mountain range might take much longer and consume more fuel.

Do Planes Follow a Straight Line?

Many people assume that flights from Copenhagen to Anchorage, for instance, would follow a straight path. However, this is not always the case. The flight path can appear curved on a flat map because the earth is a sphere. Here’s a detailed explanation:

Actual Flight Path

Consider a flight path from Copenhagen to Anchorage. The shortest path on the Earth’s surface between these two points is a curve rather than a straight line. For a plane that cruises at 80 miles per hour and has a service ceiling of 12,000 feet, flying directly over Mt. Denali (20,000 feet) can be challenging and require more fuel. Instead, pilots often choose a path that follows the Earth’s curvature, which appears to curve on a flat map but represents the shortest distance on the globe.

An actual flight path can be often traced, as shown in a sample route. This route is not random but is chosen based on several factors, including fuel efficiency and safety. The plane’s path can follow the curvature of the Earth, giving the impression of a straight line on a flat map.

Staying on a Straight Path

While the Earth is round, some flights do appear to follow a straight path. Here’s how:

Global Flights: Airlines like SAS, Lufthansa, JAL, KLM, and Air France often follow what appears as a straight path on a flat map due to the curvature of the Earth. This is not because they are flying in a literal straight line, but because they are following a great circle route, which is the shortest path on the globe. Horizontal vs. Plan View: When viewed in a plan view (flat map), the flight path may appear curved. However, if you consider the flight path in a horizontal view (looking from above the Earth), the change in direction becomes more apparent.

In conclusion, the apparent curvature of flight paths is a result of the Earth’s spherical shape combined with practical factors such as altitude, fuel efficiency, and air quality. While some flights may follow a near-straight route on a flat map, they are actually following the curvature of the Earth to achieve the most efficient and safe journey.