the Aviation Dictionary

supporting a fabric gas envelope filled with helium
(early dirigibles used flammable hydrogen). Dirigibles
are propelled by engine-driven propellers and are
capable of being maneuvered as opposed to balloons
that drift with the prevailing wind.
disbond - In composites, the separation of a bond from
one structure to another. Many times this term is used
for referring to the separationof the laminate skin to
the core structure. It is also used for a separation from
a fitting to the skin.
disc area - In rotorcraft, the area swept by the blades of
the rotor. It is a circle with its center at the hub and has
a radius of one blade length.
disbond dissi~ate
enroute/terminal ATC facilities. Discrete frequencies
are listed on Jeppesen charts.
discrimination - 1. In knowledge testing, able to detect
small differences in understanding of material tested. 2.
In a measuring instrument, means being able to detect
small differences in understanding of material between
individuals.
discriminator - In a radio receiver, a demodulator that
derives an audio signal from an incoming frequency- or
pulse-modulated RF signal.
disengage - To break the connection between
mechanical or electronic components.
dish antenna - A parabolic-shaped antenna used For
transmitting and receiving microwave signals.
disc loading - The total helicopter weight divided by the
rotor disc area.
disk area -A description of an area swept by the blades
discharge indicator disk - An indicator disk on the
exterior of an aircraft that indicates the status of the
of a helicopter.
onboard fire protection system. If the system has been disk brake - A brake that achieves brake action with a
discharged normally, a yellow disk is blown out, and if disk or disks attached to the rotating wheel being
the system has discharged because the system squeezed between brake pucks and caliper attached to
overheats, a red disk is blown out.
the aircraft gear structure.
discharge nozzle - The portion of a carburetor that
sprays the fuel into the intake airstream. Serves to
atomize the fuel for best combustion.
disconnect - To remove a load from a source of power
or the removal of one electrical device from another by
the use of a manually-operated switch or an automatic
relay.
discontinuity - In meteorology, a condition where there
is a rapid change from one type of weather phenomena
or air mass to another. A cdld front is an example of a
discontinuity.
discreet - Showing good judgment in conduct or
speech.
discrete - Not linear. A single action rather than action
changing through a range.
disk loading - A ratio of the gross weight of a
helicopter to the disk area.
dispersant - A substance that keeps particles suspended
in solution. An example is ashless dispersant (AD) oil.
It contains a substance that causes ash and other
contaminants suspended in the oil to be filtered out.
displaced threshold -When the landing area begins at a
point on the runway other than the beginning of the
runway.
display tube - An electron tube in which a stream of
electrons (cathode rays) from an electron gun impinges
upon a fluorescent screen, thus producing a bright spot
on the screen. The electron beam is deflected
electrically or magnetically to produce patterns on the
screen. Also referred to as a cathode ray tube (CRT).
discrete beacon code - See discrete code.
dissimilar metal corrosion - Corrosion caused by the
different atomic structures of metals. All metals are
discrete code -As used in the Air Traffic Control Radar listed on a nobility chart from the most vulnerable to
Beacon System (ATCRBS), any one of the 4096
selectable Mode 3/A aircraft transponder codes except
those ending in zero zero; e.g., discrete codes: 0010,
1201, 2317, 7777; non-discrete codes: 0 100, 1200,
7700. Non-discrete codes are normally reserved for
radar facilities that are not equipped with discrete
decoding capability and for other purposes such as
emergencies (7700), VFR aircraft (1200), etc.
discrete frequency - A separate radio frequency for use
corrosion (least noble) to the least vulnerable (most
noble). Magnesium and Zinc are the most vulnerable to
corrosion, while gold and platinum are the least. When
two metals are in contact with each other, the farther
apart they are on the nobility chart, the more likely
dissimilar metal corrosion will occur. All that is
necessary is for an electrolyte (usually water) to
contact the area where they touch for corrosion to
occur.
in direct pilot-controller communications in air traffic dissipate - To lessen in concentration or intensity.
control which reduces frequency congestion by Smoke can dissipate due to mixing with surrounding
controlling the number of aircraft operating on a cleaner air. Electrical power can be dissipated by being
particular frequency at one time. Discrete frequencies changed to heat by a motor, transformer, or resistor.
are normally designated for each control sector in
Aircraft Technical Book Company
P.O. Box 270
Tabernash, CO 80478
http:llwww.ACTechbooks.com