High-altitude flights have features that make them different from regular flights. These features include environmental conditions and the speed of jet performance. Flights above 25,000 ft MSL are predominantly high altitude (U.S. Department of Transportation, 2015). However, this figure may be lower, depending on air density, winds, and other external characteristics. Therefore, this paper will explain the phenomena unique to high altitude flying.
A distinctive feature of high-altitude flying is that the true airspeed (TAS) of jet increases with altitude. While indicated airspeed may remain relatively stable or slower, TAS approaches the speed of sound, and the Mach number is 0.7 to 1.2 (Brown & Holt, 2020). Since the air density is lower at high altitudes, the true airspeed buildup is necessary to maintain the pressure difference between the aircraft and the environment. At the same time, as TAS increases, there are significant changes in the control and stability of the aircraft, which makes the jet more difficult to control and may lose its maneuverability. Moreover, during a decrease in altitude, the speed of aircraft continues to increase, which can cause a Mach tuck effect (Brown & Holt, 2020). The airflow reaches supersonic speed, which can cause the nose of the aircraft to tilt forward. Stabilizing this situation requires a gradual reduction in speed and skill from the pilot.
However, modern manufacturers design jets so that their maneuverability characteristics remain unchanged during flights at high altitudes. The aircraft’s weight limits the possible flight altitude, allowing it to maintain its speed between stall buffet and high-speed buffet (Brown & Holt, 2020). However, weather conditions, turbulence, or mechanical problems can cause the pilot to exceed the operating limits of the aircraft. Low air density reduces the ability to control the aircraft and, therefore, the effectiveness of stabilization measures in the event of turbulence or disturbances during flight (Brown & Holt, 2020). Therefore, in most cases for high-altitude flying, it is recommended to use autopilot while the pilot monitors the performance of the jet in order to be able to take the necessary actions manually.
During high-altitude flying, weather conditions must be considered to anticipate the possibility of sudden turbulence due to changes in the wind flow. Turbulence is most often a consequence of wind shear, a sudden change in wind velocity and direction (U.S. Department of Transportation, 2015). In addition, the flight flow is affected by the jet stream and the polar front jet stream, which are often not tracked on circulation charts. Most changes in the direction and speed of wind currents come from sudden changes in temperature at high altitudes (U.S. Department of Transportation, 2015). Therefore, pilots must consider weather conditions to take preventive measures such as lowering altitude and avoiding turbulence in areas where it may occur. Moreover, fluctuations in barometric pressure can adversely affect a pilot’s physical condition, causing breathing difficulties (U.S. Department of Transportation, 2015). While most jets are designed to reduce the potential for collateral problems during flight, the pilot’s health is a key factor in determining whether high altitude flying is possible.
Thus, the main distinguishing feature of high-altitude flying is that flights occur in reduced air density conditions. That requires increasing the jet’s true airspeed to stabilize the pressure difference between the aircraft and the environment. In addition, at high altitudes, unpredictable weather conditions can often lead to turbulence and other disturbances during flights. Therefore, for such flights, it is necessary to consider both the aircraft’s characteristics and external circumstances that may affect the flight process. Moreover, an autopilot is recommended at high altitudes since the aircraft has less controllability and maneuverability in such conditions.
References
Brown, G. N., & Holt, M. J. (2020). The Turbine Pilot’s Flight Manual (4th ed.). Bookmasters Distribution Services. Web.
U.S. Department of Transportation. (2015). Advisory Circular 61-107B, Aircraft Operations at Altitudes Above 25,000 MSL or Mach Numbers Greater Than.75M. Web.