Altitude has a significant effect on both aircraft performance and human physiology. As altitude increases, atmospheric pressure and air density decrease, influencing how an aircraft performs and how the human body functions during flight.
Altitude and Flight
Altitude affects every aspect of flight, from aircraft performance to human performance. At higher altitudes, where atmospheric pressure is lower, takeoff and landing distances increase while climb rates decrease.
When an aircraft takes off, lift is created by the flow of air around the wings. If the air is less dense, a higher true airspeed is required to generate sufficient lift for takeoff; therefore, the ground run is longer. An aircraft that requires 745 feet of ground run at sea level requires more than double that at a pressure altitude of 8,000 feet. [Figure 1]
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| Figure 1. Takeoff distances increase with increased altitude |
At higher altitudes, aircraft engines and propellers are less efficient due to the decreased density of the air. This leads to reduced rates of climb and a greater ground run for obstacle clearance.
Altitude and the Human Body
Nitrogen and other trace gases make up 79 percent of the atmosphere, while the remaining 21 percent is life-sustaining oxygen. At sea level, atmospheric pressure is great enough to support normal growth, activity, and life. By 18,000 feet, the partial pressure of oxygen is significantly reduced, adversely affecting the normal activities and functions of the human body.
The reactions of the average person become impaired at an altitude of about 10,000 feet, but for some people impairment can occur at an altitude as low as 5,000 feet. The physiological effects of hypoxia, or oxygen deprivation, are insidious and affect people in different ways. These symptoms range from mild disorientation to total incapacitation, depending on body tolerance and altitude. Supplemental oxygen or cabin pressurization systems help pilots fly at higher altitudes and overcome the effects of oxygen deprivation.