The typical cruising altitude for a commercial airliner is about 31,000 to 42,000 feet. After taking off, pilots will climb to this altitude before leveling off. Pilots, however, take into account many factors when deciding the specific altitude for a flight. Below are some of the most important factors that affect the ideal altitude for a flight.

Fuel Efficiency

Pilots consider fuel efficiency when choosing the altitude for a flight. The air is thinner at higher altitudes, meaning there’s less drag acting against airplanes. And with less drag, airplanes are more fuel efficient. By climbing to a high altitude, pilots can fly longer distances while conserving fuel.

Lift

Pilots consider lift when choosing the altitude for a flight. While flying at high altitudes improves fuel efficiency, it can decrease lift. Air molecules are more spread out at high altitudes than at low altitudes. If an airplane flies too high, it won’t have enough air molecules under its wings to produce a sufficient amount of lift.

Weather

One of the most important factors for pilots to consider when choosing an altitude is the weather. Prior to takeoff, flight planners will analyze the weather along the route. If severe weather is present, they may choose an alternative route, such as going around inclement weather patterns. Alternatively, flight planners may recommend a higher altitude.

Aircraft Weight

The weight of an airplane will affect its ideal altitude. Heavy airplanes may lack the power to climb to a high altitude initially after taking off. As they burn fuel, however, heavy airplanes will become lighter, in which case they’ll be able to climb more easily.

Service Ceiling

All airplanes have a maximum altitude at which they can safely fly. Known as a “service ceiling,” pilots must consider it when choosing the altitude for a flight. Service ceilings can vary depending on the type of aircraft. Large jets, for instance, typically have a higher service ceiling than smaller regional and private airplanes. Regardless, pilots must stay below the aircraft’s predetermined service ceiling.

Restrictions

Pilots must consider restrictions when choosing the altitude for a flight. There are certain areas that pilots must avoid when flying. Cities and residential areas, for instance, often have prohibited flight areas. Pilots can often still fly over these areas, but they must adhere to the altitude requirements. Low-altitude flights may be prohibited because it creates noise and poses a safety risk.