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auto-separation
and collective, but cannot grossly alter steep ‘glide path’.
Rate of descent may exceed design ROD for landing gear,
but is reduced just before ground impact by sudden
increase in collective pitch; this increases lift, trading
stored rotor kinetic energy for increased aerodynamic
reaction by blades, and should result in gentle touchdown.
3 In aeroplane, descent in stalled condition, with
general direction of airflow coming from well beyond
stalling angle of attack but in grossly asymmetric condition
(see spin).
4 In aeroplane, descent in unstalled condition under
conditions apparently not greatly different from straight
and level but with stabilized spiral flight path (see spiral
dive, spiral stability). Distinct case of * which purist might
argue is incorrect usage.
5 In helicopter flying training, range of manoeuvres
designed to increase confidence and remove fear of power
failure; all power-off descents, but differ in whether they
are NPR (no power recovery) or terminated at height well
above ground by restoring at least partial power. In latter
case * terminated either by run-on-landing (running *),
run-on climb-out or moderate-flare climb-out.
auto-separation Automatic (often barometric) release of
occupant from ejection seat.
Autosevocom Automatic secure-voice communications
(DoD).
autostabilizer Loose term for autopilot, esp.. with
authority on pitch axis only.
Autosyn Trade name for remote-indicating system in
which angular position of indicator needle precisely
follows rotary sensing device moved by fluid level,
mechanical displacement or other parameter which must
be remotely measured. Sensor and indicator are essentially
synchronous electric motors.
autosynchronization Automatic synchronisation.
autothrottle Power control system for main propulsion
engines linked electro-mechanically to AFCS and
automatic-landing system so that thrust is varied automatically
to keep aircraft on glide path and taken off at
right point in autoflare; in general * will also call for
reverse thrust at full power in conjunction with automatic
track guidance (roll-out guidance), though this may be left
to discretion of pilot.
autotracking Signal processing technique that enables a
target to be automatically acquired and tracked by means
of its own image, which can be received at any operating
wavelength (usually microwave or optical).
autotrim Aircraft trim system automatically adjusted by
autopilot or other stabilising system to alter or maintain
aircraft attitude according to pilot demand or changed
distribution of weight or aerodynamic load. Usually
governs pitch only, the autopilot commanding the
elevator and the autotrim the tailplane (stabilizer).
Autovon Automatic voice network (USAF
Communications Service).
AU2GN French designation of R.R.58 alloy.
AUVS Association for Unmanned Vehicle Systems
[I adds International] (Washington, DC US).
AUW, a.u.w. All-up weight; actual aggregate weight of
particular laden aircraft at moment of weighing. For
generalized equivalent, more precise term should be used
(MRW, MTOW, etc), but AUW has advantage of being
not explicit and thus can be used to mean ‘total weight of
aircraft, whatever that happens to be’. Should never be
avalanche
used to mean MRW or MTOW. If latter are not known,
preferred term meaning ‘maximum allowable weight’ is
gross weight.
AUWE Admiralty Underwater Warfare Establishment
(UK).
AUWG Airspace Users Working Group.
AUX Auxiliary.
auxiliary bus Secondary electrical bus serving one or
more devices and often maintained at voltage different
from that of main bus.
auxiliary fin Generally, small additional fixed fin
carried, not necessarily to enhance directional stability,
well outboard on tailplane.
auxiliary fluid ignition In rocket engine, use of limited
supply of hypergolic fluid(s) to initiate combustion of
main propellants.
auxiliary inlet, auxiliary intake Extra inlet to [invariably
gas-turbine] engine to admit extra air when needed
[normally only on takeoff]. Also called supplementary air
inlet and, most commonly, suction-relief door.
auxiliary parachute Pilot parachute.
auxiliary power unit, APU Airborne power-generation
system other than propulsion or lift engines, carried to
generate power for airborne system (electrics, hydraulics,
air-conditioning, avionics, pressurization, main-engine
starting, etc). In general, term restricted to plant deriving
energy from on-board source and supplying constantspeed
shaft power plus air bleed. This would exclude a
RAT or primitive windmill-driven generator. Some ***
can provide propulsive thrust in emergency (see MEPU).
auxiliary rigging lines Branching from main parachute
rigging lines to distribute load more evenly around
canopy.
auxiliary rotor In a classical helicopter [one main rotor],
the rotor provided to counter drive torque and control
fuselage azimuth. This is preferably called the tail rotor.
auxiliary tank Fuel tank additional to main supply, esp.
that can readily be removed from aircraft (see reserve
tank, external tank, drop tank).
AV 1 Air vehicle.
2 Audio-visual.
3 Aft vectoring (nozzle mode).
AVA 1 Automatic voice advice.
2 Applied vector analysis.
3 Aeropark Volunteers Assocation [Derby DE24 0ED]
(UK).
AVAD Automatic voice alert[ing] device.
AVADS Autotrack Vulcan air-defense system (USA).
aval, Aval Available.
availability 1 Symbol A, proportion of time aircraft is
serviceable and ready for use, expressed as decimal fraction
over period or as number of hours per day or days per
uptime
month. Also expressed as –––––––––––––––– .
uptime + downtime
2 Period which must elapse between purchase of
aircraft, usually second-hand, and handover to customer.
avalanche 1 Any of several processes involving ions or
electrons in which collisions generate fresh ions or electrons
which in turn go on to have their own collisions. In
* tube electrons or other charged particles are accelerated
in electric field to generate additional charged particles
through collisions with neutral gas atoms or molecules. In
semiconductor devices * effect occurs when potential in
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