How far up do planes fly?

As an expert in the field of aeronautics, I can provide you with a detailed explanation of the altitudes at which commercial aircraft typically operate and the reasons behind these limitations.

Step 1: English Explanation

Commercial airplanes, particularly large passenger planes, are designed to fly within a specific range of altitudes. The cruising altitude for most commercial aircraft is typically between **8,000 to 12,000 meters (26,000 to 39,000 feet)** above sea level. This range is known as the flight level or FL, which is a standard for international aviation that refers to the height of an aircraft above sea level in hundreds of feet.

There are several reasons why aircraft fly within this range:


1. Atmospheric Conditions: Above 12,000 meters, the air becomes too thin for the aircraft's engines to operate efficiently. The engines require a certain amount of oxygen to combust fuel, and at higher altitudes, the reduced air density makes it difficult for the engines to generate the necessary thrust.


2. Oxygen Levels: At high altitudes, the oxygen level in the atmosphere drops significantly. This is why aircraft cabins are pressurized. If the aircraft were to fly much higher, the pressurization systems would have to work harder, and the risk to passengers and crew from reduced oxygen levels would increase.


3. Temperature: The temperature drops as altitude increases. While modern aircraft are designed to withstand cold temperatures, flying too high could lead to issues with the aircraft's systems and materials.


4. Fuel Efficiency: The air is less dense at higher altitudes, which means there is less resistance, allowing the aircraft to fly more efficiently. However, there is a sweet spot in terms of fuel consumption and engine performance, which is typically found within the aforementioned range.


5. Safety and Air Traffic Control: Operating within regulated altitudes allows for better air traffic control and reduces the risk of mid-air collisions. It also facilitates more predictable flight paths and easier communication with ground control.


6. Structural Design: Aircraft are designed to withstand specific pressure differentials. Flying too high could put undue stress on the aircraft's structure.

The International Standard Atmosphere (ISA) model provides a standard set of conditions for sea level, which is used as a reference for aircraft performance calculations. However, the actual conditions can vary, and pilots must adjust their aircraft's performance accordingly.

It's worth noting that some high-altitude aircraft, such as military jets or specialized research planes, can fly much higher, sometimes up to 18,000 meters (59,000 feet) or more. However, these aircraft have different design considerations and are not subject to the same commercial constraints as passenger planes.

Step 2: Divider

Large passenger planes can't fly much higher than about 12 kilometers (7.5 miles). The air is too thin above that altitude to hold the plane up.