Any period of time during an aircraft's flight when its altitude decreases
In
aeronautics
, a
descent
is any time period during
air travel
where an
aircraft
decreases
altitude
, and is the opposite of an
ascent
or
climb
.
Descents are part of normal procedures, but also occur during emergencies, such as rapid or
explosive decompression
, forcing an emergency descent to below 3,000 m (10,000 ft) and preferably below 2,400 m (8,000 ft), respectively the maximum temporary safe altitude for an
unpressurized
aircraft and the maximum safe altitude for extended duration.
[1]
[a]
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
.
Normal descents
[
edit
]
Intentional descents might be undertaken to
land
, avoid other air traffic or 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.
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
.
Rapid descents
[
edit
]
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
.
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).
Tactical descent
[
edit
]
A tactical descent is a maneuver typically used only by military aircraft. It consists of a steep angle dive to lose altitude rapidly, with the use of
thrust reversers
to prevent excessive speed.
[2]
[3]
Dives
[
edit
]
Ju 87B "Stuka" dive bomber
A
dive
or
nosedive
[4]
[5]
[6]
is "a steep descending flight path".
[7]
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 flying
to build speed for the performance of stunts, and by
dive bombers
to approach a target quickly while minimizing exposure to enemy fire before the dive, and in order to increase accuracy of the bombing. 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 4,600 m (15,000 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 (270 to 320 kn; 310 to 370 mph), until it had gone some 90% of the way to the ground, releasing its bombs at a minimum height of 450 m (1,480 ft).
[8]
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.
[8]
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.
See also
[
edit
]
Notes
[
edit
]
References
[
edit
]
- ^
Manager, FAA Transport Airplane Directorate, Aircraft Certification Service, ANM-100 (March 24, 2006).
"Interim Policy on High Altitude Cabin Decompression (Reference Amendment 25-87)"
(PDF)
. U.S. Federal Aviation Administration. p. 5. Archived from
the original
(PDF)
on 2017-03-08
. Retrieved
2011-04-02
.
The primary means to ensure occupant survivability rests in quickly bringing the occupants to a cabin pressure where they can survive (i.e., a lower cabin pressure altitude as given in the table below). Airplane DAH should use design features that facilitate rapid airplane descent from high altitudes to ensure that the occupants will not be subjected to pressure altitudes for durations longer than those given in the following table.
{{
cite web
}}
: CS1 maint: multiple names: authors list (
link
) CS1 maint: numeric names: authors list (
link
)
- ^
Cenciotti, David (2019-08-21).
"This Is What A Tactical Descent In A C-17 Globemaster III Cargo Aircraft Looks Like"
.
The Aviationist
. Retrieved
2024-01-29
.
- ^
Newdick, Thomas (2021-08-03).
"Watch This C-17 Engage Its Thrust Reversers In Mid-Air To Make An Extremely Rapid Descent"
.
The Drive
. Retrieved
2024-01-29
.
- ^
Newman, John G.; Łodej, Sylwester (2013-12-01).
Token: A Journal of English Linguistics (Volume 2): Volume 2
. Jan Kochanowski University.
- ^
"nosedive | Definition of nosedive in English by Oxford Dictionaries"
.
Oxford Dictionaries | English
. Archived from
the original
on August 30, 2018
. Retrieved
2018-08-29
.
- ^
"nosedive Meaning in the Cambridge English Dictionary"
.
dictionary.cambridge.org
. Retrieved
2018-08-29
.
- ^
Crane, Dale:
Dictionary of Aeronautical Terms, third edition
, page 168. Aviation Supplies & Academics, 1997.
ISBN
1-56027-287-2
- ^
a
b
Griehl, Manfred.
Junker Ju 87 Stuka
. London/Stuttgart: Airlife Publishing/Motorbuch, 2001.
ISBN
1-84037-198-6
.
External links
[
edit
]
|
---|
Main phases
| |
---|
Related topics
| |
---|