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Sec[s]
Sec[s] 1 Second[s] (contrary to SI but still ICAO).
2 Secondary.
Secad SEC (10) algorithm development (NAWC).
Secam Safety, efficiency and capacity of ATM (7)
methodologies (Euret).
Secant Separation and control of aircraft, nonsynchronous
techniques.
secant modulus E, slope of stress/strain curve to any
point; thus equal to modulus of elasticity up to limit of
proportionality, thereafter varying with applied stress to
point of rupture.
SECBM Seventeen-sixty [MIL-Std 1760] enhanced
conventional bomb-module (USAF).
SecDef Secretary of State for Defense (US).
SECL Symmetrical emitter-coupled logic.
Seco, SECO S-IVB engine cut-off (Apollo).
second 1 SI unit of time, symbol s, = 9,192,631,770
transitions between two ground states of Cs-133 atom.
2 Unit of plane angular measure, symbol " = 4.848 ×
10 -6 .rad.
secondary Small area of low pressure on periphery of
large cyclone.
secondary airflow That used to dilute and cool flame in
gas-turbine combustor.
secondary airport Smaller airport at city possessing hub
airport.
secondary battery Electric battery rechargeable by
reverse DC current.
secondary bending In a beam or column whose chief
applied stress is transverse, that bending moment due to
axial load.
secondary controls See secondary flight controls.
secondary depression See secondary.
secondary display Simplified display of flight instruments
enabling aircraft to be safely flown following
failure of primary.
secondary electron emission Flow of electrons from
metal surface under bombardment by high-energy electrons
or protons.
secondary emission Ejection of subatomic particles
and/or photons from atoms or particles subjected to
primary radiation, eg cosmic rays.
secondary explosion Explosion at surface target caused
by air attack but additional to explosions of air-dropped
ordnance.
secondary fan airflow Airflow through fan which does
not pass through engine core.
secondary flight controls Those used intermittently to
change lift or speed but not trajectory; eg flaps, slats,
Krügers, airbrakes, droops and, except in DLC, spoilers.
secondary frequency Assigned to an aircraft as standby
in air/ground.
secondary front One formed within an air mass.
secondary glider Not defined, but training glider more
advanced than primary and with enclosed cockpit.
Generally any glider intermediate between primary and
Standard Class sailplane.
secondary great circle See meridian.
secondary heat-exchanger That which rejects heat to
atmosphere from secondary circuit heated by primary
heat-exchanger.
secondary holes Those admitting secondary air to
combustor.
secondary instruments 1 Those giving information
second segment
unconnected with gross flight trajectory, ie not a primary
flight instrument.
2 Those whose calibration is determined by comparison
with an absolute instrument.
secondary members See secondary structure.
secondary modulus Modulus of elasticity for composite
of other two-component material (esp. two-metal components)
beyond point at which weaker material yields.
secondary nozzle Annular nozzle surrounding primary
nozzle of jet engine through which may pass cooling
airflow, inlet excess and various other flows around
engine.
secondary power system Mechanical power system on
board aircraft other than main engines, eg shaft-driven
accessories, gearboxes, gas-turbine starter, APU, EPU or
MEPU, inter-engine cross-shafting and major bleed
ducting with air-turbine drives if fitted.
secondary radar Radar in which interrogatory pulse is
sent to distant transponder which is triggered to send back
a different pulse code to originator. Examples are
airborne DME triggering ground DME facility and
ground SSR triggering airborne transponder.
secondary radiation Usually synonymous with
secondary emission.
secondary stall Rotating stall [engine].
secondary stress That resulting from deflection under
load, eg of end-loaded column in bending.
secondary structure Structural parts of airframe whose
failure does not immediately imperil continued safe flight.
secondary surveillance radar Ground radar which interrogates
air traffic with identifiable codes of pulses,
triggers distinctive response from each target, extracts
plots and assigns identity to each, normally presented as
flight number, altitude and other information beside
target on radar display [Mode A provides coded target
identiy, C altitude and S selective interrogation]. Aerial
normally slaved in azimuth to main surveillance (primary)
radar and may be on-mounted.
secondary winding That of transformer, magneto or
other electrical device from which output is supplied.
second buy See option (1); originally Lockheed term for
option with paid deposit.
second day In all-out war, assumption that enemey’s
long-range air defences are destroyed.
second dicky Co-pilot (UK, colloq.).
second-line servicing That carried out over planned
period when aircraft is out of line service, sometimes at
special off-base facility.
second moment of area Moment of inertia of a structural
section whose mass is unity; SI m 4 = 115.86183 ft 4 , cm 4 =
0.024025 in 4 .
second pilot 1 Person designated as second pilot in flight
crew to assist PIC; in commercial crew usually has rank of
First Officer. In ASCC definition: ‘not necessarily qualified
on type’.
2 Unofficial term for passenger who has completed
short [usually 8–10h] flying course to enable him or her to
land light [12,500lb] aircraft following incapacitation of
pilot.
second segment Second segment of normal takeoff for
large or advanced aerooplanes beginning at gear
retraction at V 2 and maintaining this speed in climb to top
of climb at end of segment when aircraft is levelled out, or
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