Descent (aircraft)
Encyclopedia
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 rapid or explosive decompression
, forcing an emergency descent to below 10000 feet (3,048 m) and preferably below 8000 feet (2,438.4 m), respectively the maximum temporary safe altitude for an unpressurized
aircraft and the maximum safe altitude for extended duration.
An example of explosive decompression is Aloha Airlines Flight 243
. Involuntary descent might occur from a decrease in power, decreased lift (wing icing), an increase in drag
, or flying in an air mass moving downward, such as a terrain induced downdraft, near a thunderstorm
, in a downburst
, or microburst
.
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.
—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
.
Helicopters which lose power do not 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 increase lift to slow the rate of descent to a normal landing (but without extended hovering).
to build speed for the performance of stunts, and by dive bomber
s to approach a target quickly while minimizing exposure to enemy fire before the dive. A dive may also be used as an emergency maneuver, for example to extinguish an engine fire.
Pilots of the World War II dive bomber known as the Stuka
particularly noted the effects of the dive. Beginning at a height of 4600 metres (15,091.9 ft), the Stuka would roll 180°, automatically nosing into a dive. The aircraft would then dive at a 60-90° angle, holding a constant speed of 500 to 600 km/h (310.7 to 372.8 mph), until it had gone some 90% of the way to the ground, releasing its bombs at a minimum height of 450 metres (1,476.4 ft). Once the pilot released the bomb and initiated an automatic pull-out mechanism by depressing a knob on the control column, the aircraft automatically began a six g
pullout. The tremendous g-forces to which pilots were subjected during this maneuver could lead to momentary blackouts, necessitating the inclusion of mechanisms to automate pullout from the dive while the pilot was unconscious.
Climb
thumb|right|An [[Embraer ERJ 145]] climbingIn aviation, the term climb refers both to the actual operation of increasing the altitude of an aircraft and to the logical phase of a typical flight following take-off and preceding the cruise, during which an increase in altitude to a predetermined...
. Descents are an essential component of an approach to landing
Landing
thumb|A [[Mute Swan]] alighting. Note the ruffled feathers on top of the wings indicate that the swan is flying at the [[Stall |stall]]ing speed...
. Other intentional descents might be to avoid traffic, poor flight conditions (turbulence, icing conditions
Icing conditions
In aviation, icing conditions are those atmospheric conditions that can lead to the formation of water ice on the surfaces of an aircraft, or within the engine as carburetor icing. Inlet icing is another engine-related danger, often occurring in jet aircraft. These icing phenomena do not...
, or bad weather), clouds (particularly under visual flight rules
Visual flight rules
Visual flight rules are a set of regulations which allow a pilot to operate an aircraft in weather conditions generally clear enough to allow the pilot to see where the aircraft is going. Specifically, the weather must be better than basic VFR weather minimums, as specified in the rules of the...
), 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 rapid or explosive decompression
Decompression
Decompression has several meanings:* Decompression , the release of pressure and the opposition of physical compression* Decompression sickness, a condition arising from the precipitation of dissolved gases into bubbles inside the body on depressurization* Decompression , a procedure used to treat...
, forcing an emergency descent to below 10000 feet (3,048 m) and preferably below 8000 feet (2,438.4 m), respectively the maximum temporary safe altitude for an unpressurized
Cabin pressurization
Cabin pressurization is the pumping of compressed air into an aircraft cabin to maintain a safe and comfortable environment for crew and passengers when flying at altitude.-Need for cabin pressurization:...
aircraft and the maximum safe altitude for extended duration.
An example of explosive decompression is Aloha Airlines Flight 243
Aloha Airlines Flight 243
Aloha Airlines Flight 243 was a scheduled Aloha Airlines flight between Hilo and Honolulu in Hawaii. On April 28, 1988, a Boeing 737-200 serving the flight suffered extensive damage after an explosive decompression in flight, but was able to land safely at Kahului Airport on Maui. The only...
. Involuntary descent might occur from a decrease in power, decreased lift (wing icing), an increase in drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
, or flying in an air mass moving downward, such as a terrain induced downdraft, near a thunderstorm
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
, in a downburst
Downburst
A downburst is created by an area of significantly rain-cooled air that, after reaching ground level, spreads out in all directions producing strong winds. Unlike winds in a tornado, winds in a downburst are directed outwards from the point where it hits land or water...
, or microburst
Microburst
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. There are two types of microbursts: wet microbursts and dry microbursts...
.
Normal descents
Normal descents take place at a constant airspeed and constant angle of descent (3 degree final approachFinal approach (aviation)
A final approach is the last leg in an aircraft's approach to landing. In aviation radio terminology, it is often shortened to "final".In a standard airport landing pattern, which is usually used under visual meteorological conditions , aircraft turn from base leg to final within one to two miles...
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
Glider (sailplane)
A glider or sailplane is a type of glider aircraft used in the sport of gliding. Some gliders, known as motor gliders are used for gliding and soaring as well, but have engines which can, in some cases, be used for take-off or for extending a flight...
. If the nose is too high for the chosen power the airspeed will decrease until eventually the aircraft stalls
Stall (flight)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...
, or loses lift.
Rapid descents
Rapid descents relate to dramatic changes in cabin air pressure—even pressurized aircraftCabin pressurization
Cabin pressurization is the pumping of compressed air into an aircraft cabin to maintain a safe and comfortable environment for crew and passengers when flying at altitude.-Need for cabin pressurization:...
—and can result in discomfort in the middle ear
Middle ear
The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...
. 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
Valsalva maneuver
The Valsalva maneuver or Valsalva manoeuvre is performed by moderately forceful attempted exhalation against a closed airway, usually done by closing one's mouth and pinching one's nose shut...
.
Helicopters which lose power do not simply fall out of the sky. In a maneuver called autorotation
Autorotation
In aviation, autorotation refers to processes in both fixed-wing and rotary-wing aircraft. The term means significantly different things in each context....
, 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 increase lift to slow the rate of descent to a normal landing (but without extended hovering).
Dives
A dive may technically be described as "a steep descending flight path". While there is no specific definition for what degree of steepness transforms a downward trajectory into a dive, it is necessarily a rapid, nose-forward descent. Dives are used intentionally in aerobatic flyingAerobatics
Aerobatics is the practice of flying maneuvers involving aircraft attitudes that are not used in normal flight. Aerobatics are performed in airplanes and gliders for training, recreation, entertainment and sport...
to build speed for the performance of stunts, and by dive bomber
Dive bomber
A dive bomber is a bomber aircraft that dives directly at its targets in order to provide greater accuracy for the bomb it drops. Diving towards the target reduces the distance the bomb has to fall, which is the primary factor in determining the accuracy of the drop...
s to approach a target quickly while minimizing exposure to enemy fire before the dive. A dive may also be used as an emergency maneuver, for example to extinguish an engine fire.
Pilots of the World War II dive bomber known as the Stuka
Junkers Ju 87
The Junkers Ju 87 or Stuka was a two-man German ground-attack aircraft...
particularly noted the effects of the dive. Beginning at a height of 4600 metres (15,091.9 ft), the Stuka would roll 180°, automatically nosing into a dive. The aircraft would then dive at a 60-90° angle, holding a constant speed of 500 to 600 km/h (310.7 to 372.8 mph), until it had gone some 90% of the way to the ground, releasing its bombs at a minimum height of 450 metres (1,476.4 ft). Once the pilot released the bomb and initiated an automatic pull-out mechanism by depressing a knob on the control column, the aircraft automatically began a six g
G-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
pullout. The tremendous g-forces to which pilots were subjected during this maneuver could lead to momentary blackouts, necessitating the inclusion of mechanisms to automate pullout from the dive while the pilot was unconscious.