Planes generally don't fly much higher than 40,000 feet due to a combination of factors including pilot oxygen requirements and diminishing returns on efficiency.
Factors Limiting Flight Altitude
Several factors contribute to the altitude ceiling for commercial and other aircraft:
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Oxygen Availability for Pilots: Above 40,000 feet, even with pure oxygen, the air pressure is so low that pilots are operating at the limit of their physiological performance. At this altitude, the air pressure is around 5 inHg (inches of mercury), meaning even breathing pure oxygen only provides an equivalent of 4-5 inHg of oxygen. This is considered the limit for maintaining optimal pilot function.
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Aircraft Design and Performance: Aircraft are designed to operate most efficiently within a specific altitude range. While some aircraft can fly higher, doing so might not be economically viable.
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Atmospheric Conditions: Higher altitudes can experience more extreme weather, including stronger winds and turbulence. While jet streams at higher altitudes can aid in ground speed, they aren't always beneficial and can be unpredictable.
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Cabin Pressurization: Maintaining a comfortable and safe cabin pressure becomes more challenging and energy-intensive at higher altitudes. While planes are pressurized, extreme altitudes would require even greater pressurization systems, adding weight and complexity.
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Diminishing Returns: While higher altitudes offer reduced air resistance, there is a point where the benefits of less drag are offset by the increased fuel consumption required to reach and maintain that altitude, as well as increased stress on aircraft systems.
In summary, while some aircraft are capable of flying above 40,000 feet, a combination of human physiological limitations, engineering constraints, and economic considerations generally keeps commercial flight altitudes below this level.
