Why do planes fly at 40000 feet?

Planes are *optimized* to fly at certain heights to maximize the efficiency of their engines and their fuel consumption. So jet planes can fly a lot higher than propeller planes, so they do. They fly between 20,000 feet and 40,000 feet because they are designed and optimized to do just that.



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Aerodynamic altitude: If a commercial airliner flies too high, it will encounter less dense air passing over the wings to create lift. This can cause the plane to stall and fall out of control. Depending on the weather conditions and aircraft weight, this can occur anywhere between 40,000 and 45,000 feet.

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At 40,000 feet its only 2.72 PSI. If outside air gets into the mask and is breathed, it contains one-fifth (20 percent) of the oxygen necessary for survival at 40,000 feet. The time of useful consciousness on ambient air only at 40,000 feet is 15 to 20 seconds.

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The maximum height that a commercial airplane is allowed to reach when they fly is 42,000 feet, as this is the universally approved maximum altitude. This max altitude for airplanes is known as the “service ceiling.” Most commercial air jets fly at such a high altitude because it is known to optimize efficiency.

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It refers to altitudes above a certain point where the amount of oxygen is insufficient to sustain human life for an extended time span. This point is generally tagged as 8,000 m (26,000 ft, less than 356 millibars of atmospheric pressure).

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Whether flying at night or during the day, pilots need to see some kind of horizon. They use this to determine the airplane's attitude. At night pilots will turn their gaze from outside to inside and use the artificial horizon. The artificial horizon is normally a simply globe split into two hemispheres.

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Techincally, there is only one way for the aircraft to remain hanging motionless in the air: if weight and lift cancel each other out perfectly, and at the same time thrust and drag cancel each other out too. But this is incredibly rare. To stay in the air and sustain its flight, an aircraft needs to be moving forward.

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All airplanes will be exposed to drag during flight. They must overcome this aerodynamic force to achieve and maintain lift. Otherwise, airplanes would essentially fall out of the sky. Air brakes are control surfaces that increase drag so that airplanes slow down during flight.

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A rough estimate of the probability of an airplane going down due to an emergency is about 1 in 11 million, meaning it would take us quite a few lifetimes before actually experiencing a plane crash. That's a whopping 0.00001% chance that something will go terribly wrong on your flight.

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An overloaded aircraft may not be able to leave the ground, or if it does become airborne, it may exhibit unexpected and unusually poor flight characteristics. If not properly loaded, the initial indication of poor performance usually takes place during takeoff.

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As it turns out, along with being thinner, research suggests people worldwide who live at high altitudes have a lower incidence of both cancer and heart disease than folks who live closer to sea level. Note that these studies were done decades ago. We've known the health advantages of high altitude for a long time.

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One thing that pilots and prospective aircraft dispatchers need to understand is that there is not one universal safe altitude since some terrains or objects may be taller than others. Rather, the accepted metric is that this altitude needs to be at least 500 feet above the terrain or obstacle in question.

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Most flights are intended to spend as little time as possible over water, since storms are more common over the ocean than on land. An aircraft would not be safe to fly over the Pacific Ocean due to the stormy weather and frequent lightning strikes that occur there.

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Technically, no. Day/night has nothing to do with it. If anything, pilots that are flying under Visual Flight Rules (VFR) might opt to fly higher than during the day to improve their odds and better avoid inadvertently flying near terrain or obstructions that are less visible.

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