Descent (aeronautics): Difference between revisions
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A '''descent''' during air travel is any portion where an aircraft decreases altitude, and is the opposite of an ascent or [[climb]]. 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. As well what may require an aircraft descent is during emergencies, such as a sudden [[decompression]] forcing an emergency descent to below 10,000ft, the maximum safe altitude for an [[Cabin pressurization|unpressurized]] aircraft. An example of this is [[Aloha Flight 243]]. Involuntarily descent might occur from a decrease in power |
A '''descent''' during air travel is any portion where an aircraft decreases altitude, and is the opposite of an ascent or [[climb]]. 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. As well what may require an aircraft descent is during emergencies, such as a sudden [[decompression]] forcing an '''emergency descent''' to below 10,000ft, the maximum safe altitude for an [[Cabin pressurization|unpressurized]] aircraft. An example of this is [[Aloha Flight 243]]. '''Involuntarily descent''' might occur from a decrease in power or lift (e.g. due to wing [[icing conditions|icing]]); an increase in [[Drag (physics)|drag]]; or flying in a downward-moving [[air mass]], such as a terrain induced [[downdraft]], near a [[thunderstorm]], or in a [[downburst]] or [[microburst]]. |
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Rapid descents relate to dramatic changes in cabin [[air pressure]]—even [[Cabin pressurization|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]]. |
Rapid descents relate to dramatic changes in cabin [[air pressure]]—even [[Cabin pressurization|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]]. |
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Revision as of 02:19, 15 June 2010
 | This article includes a list of references, related reading, or external links, but its sources remain unclear because it lacks inline citations. (August 2009) |
A descent during air travel is any portion where an aircraft decreases altitude, and is the opposite of an ascent or climb. 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. As well what may require an aircraft descent is during emergencies, such as a sudden decompression forcing an emergency descent to below 10,000ft, the maximum safe altitude for an unpressurized aircraft. An example of this is Aloha Flight 243. Involuntarily descent might occur from a decrease in power or lift (e.g. due to wing icing); an increase in drag; or flying in a downward-moving air mass, such as a terrain induced downdraft, near a thunderstorm, or in a downburst or microburst.
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.
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.
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).