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Encyclopedia > Descent (aircraft)

A descent during air travel is any portion where an aircraft decreases altitude, and is the opposite of an ascent. Descents are an essential component of an approach to landing. Other intentional descents might be to avoid traffic, poor flight conditions (turbulence, icing conditions, or bad weather), clouds (particularly under visual flight rules), to see something lower, to enter warmer air (see adiabatic lapse rate), or to take advantage of wind direction of a different altitude, particularly with balloons. Involuntarily descent might occur from a decrease in power, lift (wing icing), an increase in drag, or flying in an air mass moving downward, such as a terrain induced downdraft, rotor, near a thunderstorm, in a downburst or microburst. Landing is the last part of a flight, where a flying animal or aircraft returns to the ground. ... In aviation, icing conditions are those atmospheric conditions that can lead to the formation of water ice on the surfaces of the aircraft, or as carburetor icing within the engine. ... Visual flight rules (VFR) are a set of aviation regulations under which a pilot may operate an aircraft, if weather conditions are sufficient to allow the pilot to visually control the aircrafts attitude, navigate, and maintain separation with obstacles such as terrain and other aircraft. ... The adiabatic lapse rate is the rate of temperature change that occurs in an atmosphere as a function of elevation, assuming that air behaves adiabatically. ... For a solid object moving through a fluid or gas, drag is the sum of all the aerodynamic or hydrodynamic forces in the direction of the external fluid flow. ... A downdraft is downward moving air, usually the direct result of air convection within the thunderstorm. ... A roll cloud associated with a heavy or severe thunderstorm over Enschede, The Netherlands. ... A downburst is a column of sinking air that is capable of producing damaging straight-line winds over 100 mph, similar to, but distinguishable from tornadoes. ... A photograph of the surface curl soon after an intense microburst impacted the surface A microburst is a very localized column of sinking air, producing damaging divergent and straight-line winds at the surface that are similar to but distinguishable from tornadoes which generally have convergent damage. ...


Rapid descents relate to dramatic changes in cabin air pressure—even pressurized aircraft—and can result in discomfort in the middle ear. Relief is achieved by decreasing relative pressure by equalizing the middle ear with ambient pressure ("popping ears") through swallowing, yawning, chewing, or the valsalva maneuver. Air pressure can refer to the pressure of air environmentally, as in atmospheric pressure, or to the pressure of air in an inflatable or other sealed object, as might be read by a tire-pressure gauge. ... For an alternative meaning, see ear (botany). ... Relative pressure is pressure as compared to atmospheric pressure, or the average pressure of air and Earths sea level — 101. ... A Valsalva maneuver is any attempted exhalation against a closed glottis or against a closed mouth and nose. ...


Normal descents take place at a constant airspeed and constant angle of descent (3 degree final approach at most airports). The pilot controls the angle of descent by varying engine power and pitch angle (lowering the nose) to keep the airspeed constant. Unpowered descents (such as engine failure) are steeper than powered descents but flown in a similar way as a glider. If the nose is too high for the chosen power the airspeed will decrease until eventually the aircraft stalls, or loses lift. The pitch angle of a charged particle is the angle between the particles parrallel motion the local magnetic field. ... Gliders are heavier-than-air aircraft primarily intended for un-powered flight. ... In aerodynamics, a stall is a condition in which an excessive angle of attack causes loss of lift due to disruption of airflow. ...


Helicopters which lose power don't simply fall out of the sky. In a maneuver called autorotation, the pilot configures the rotors to spin faster driven by the upward moving air, which limits the rate of descent. Very shortly before meeting the ground, the pilot changes the momentum stored in the rotor to increased lift to slow the rate of descent to a normal landing (but without extended hovering). Autorotations are used in helicopters to perform power off landings from altitude in the event of an engine failure. ...


See also

A Ryanair Boeing 737 takes off from Bristol International Airport, England Takeoff is the phase of flight where an aircraft transitions from moving along the ground (taxiing) to flying in the air (see flight), usually from a runway. ... Boeing 747 in cruise at roughly 35000 feet, showing contrails from the four engines. ... Landing is the last part of a flight, where a flying animal or aircraft returns to the ground. ...

References

  • FAA terminal procedures index
  • Flight school ground course on landing
  • A helicopter school autorotation guide
  • FAA rotorcraft pilot testing standards
  • FAA airplane pilot testing standards

  Results from FactBites:
 
CFI Insights "The Descent" (1821 words)
As with climb, the weight of the aircraft, the location of its centre of gravity, density altitude and humidity, use of carburetor heat, deployment of flaps and landing gear, turbulence and the pilot’s accuracy and skill in maintaining correct angle of attack and airspeed all affect an aircraft’s descent.
Centre of gravity location affects descent in the sense that an aircraft with a more forward centre of gravity is, effectively, a heavier aircraft resulting from the increase in down-force developed by the tail-plane which acts on the aircraft as though it were weight.
With the aircraft bouncing all about the sky, it may be a bit more challenging to maintain constant airspeed and angle of attack than when operating in still air.
  More results at FactBites »

 
 

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