The Effect of Atmospheric Pressure on High Altitude Living and Aviation

The relationship between atmospheric pressure and altitude is inverse. As altitude increases, air pressure decreases, and vice versa. Humans living at high altitudes face unique challenges, particularly when atmospheric pressure drops further. This article will explore the relationship between atmospheric pressure and altitude, how a decrease in atmospheric pressure would affect humans and aviation, and the impact on altimeter accuracy.

Understanding Atmospheric Pressure and Altitude

Air pressure decreases with increasing altitude. Approximately two-thirds of the atmosphere lies below 18,000 feet, while the remaining portion extends to over 200,000 feet. The weight of the air above a point creates the air pressure. At sea level, the atmospheric pressure is 14.7 pounds per square inch.

The decrease in air pressure follows an approximately exponential relationship with altitude. The air becomes less dense, roughly by a factor of 10 for every 20 kilometers increase in altitude. The exact rate can vary due to temperature changes.

The Impact of Lower Atmosphere Pressure

Humans living at high altitudes already experience lower atmospheric pressure. Adaptation is possible up to a certain point, but below certain levels, the low air pressure becomes dangerous. For example, if the atmospheric pressure decreased by 25%, humans could not live at 4,000 meters above sea level (AMSL) as they do now. This drastic change would reduce the 'death zone' from 8,000 meters to 6,000 meters.

Altimeters and Atmospheric Pressure Measurement

All airplanes use barometric altimeters to measure altitude. These altimeters sense the static pressure outside the aircraft and convert it to an altitude reading using a fixed table and the baro-setting selected by the pilot. Historically, sensitive altimeters were called sensitive altimeters, but now they are simply called altimeters.

Paul Kollsman invented the sensitive altimeter and is still referred to as the 'Kollsman window' by old pilots. The built-in table assumes a standard atmosphere (ISA) and a baro-setting of 1003 millibars or 29.92 inches of mercury. In reality, the atmospheric conditions rarely match ISA, leading to a display of pressure altitude. This means that if all aircraft are set to the same baro-setting, they will show an equal error in true altitude, crucial for maintaining safe separation in Instrument Flight Rules (IFR) conditions.

The Evolution of Altimeter Accuracy in Aviation

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The primary goal of a barometric altimeter is to maintain separation between aircraft in IFR conditions. However, this approach has limitations. Modern GPS technology allows for precise position fixing, leading to the introduction of Reduced Vertical Separation Minimums (RVSM). RVSM was first implemented over the North Atlantic in 2000, allowing aircraft to fly only 1000 feet apart above Flight Level 290 (29,000 feet).

Under RVSM, aircraft must pass a rigorous ground test and fly over a precision radar to measure their actual height. Modern autopilots and electronic air data computers are used to achieve precise altitude control. Altimeter errors, especially in older jets, were significant, leading to the development of sophisticated systems to minimize these errors.

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The shift from altitude-based separation to position-based separation aligns with the evolving technology in aviation. GPS technology now offers greater precision, making it possible to maintain separation without relying solely on barometric altimeters. The accurate position fixing from GPS could potentially reduce the need for the current 1,000-foot separation in IFR airspace.

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The future of aviation safety and airspace management looks promising as new technologies continue to evolve. As GPS becomes more reliable and precise, the reliance on barometric altimeters may diminish, leading to safer and more efficient airspace operations.

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Conclusion

The relationship between atmospheric pressure and altitude is crucial for understanding the challenges faced by individuals living at high altitudes and the aviation industry. As technology advances, the dependence on barometric altimeters is being reconsidered, paving the way for safer and more efficient aviation operations.

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Keywords: atmospheric pressure, high altitude, altimeter accuracy