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BACEA
BACEA British Airport Construction and Equipment
Association.
Bacimo Battlespace atmospheric and cloud impacts on
military operations (USAF).
back 1 Of drag curve, aeroplane flight below VIMD, in
which reduction in speed results in increased drag.
2 Of propeller or rotor blade, surface corresponding to
upper surface of wing.
3 Rear cockpit of tandem two-seat aircraft, especially
combat type (hence GIB).
back beam In any beam system, especially ILS localizer,
reciprocal beam on other side of transmitter.
back bearing Direction observed from aircraft holding
steady course of fixed object over which it has recently
passed; reciprocal of track.
backboard 1 Multilayer circuit board.
2 Specially narrow stretcher (litter) for carrying injured
passengers along aisles.
back burner To be on * = not urgent, temporarily shelved.
back contamination Contamination of Earth by
organisms introduced by spacecraft and crews returning
from missions.
back course Course flown along back beam, on
extended centreline of runway away from airfield.
backdrive Where controlled device drives control input,
eg thrust levers in Autothrottle mode, or when active
motor [e.g. for tailplane] drives failed unit.
backed-off Jet engine slid out of fuselage on rails for
maintenance, ready to be at once re-installed.
backfire Premature ignition of charge in piston engine
cylinder such that flame travels through still-open inlet
valve(s) and along induction manifold.
backfit Retrofit (US usage).
background Ambient (usually supposed steady-state)
level of intensity of a physical phenomenon against which
particular signal is measured. If signal amplitude never
exceeds that of background, it cannot be detected. Thus:
* clutter (radar), * count (radiation), * luminance, * noise
(this has two meanings: noise in electronic circuit, and
ambient level of aural noise at airport or elsewhere). See
microwave *.
background check Post – 9/11 investigation of personnel
(US Dept. of Justice).
backing 1 General effort by hardware manufacturer to
support his products after they reach customer.
2 Change in direction of prevailing wind in counterclockwise
direction viewed from above; thus, from S to
SE.
backing up Rearwards taxiing of freight aircraft to
loading dock, using reverse thrust.
backlash In any mechanism, lost motion due to loose
fitting or wear.
backlobe Radiation lobe from an antenna in the reverse
direction to the main beam.
backlog In manufacturing programme, items sold but
not yet delivered
backout Any reversal of countdown, usually due to technical
hold or fault condition.
backpack 1 Personal parachute pack worn on back
(usually thin enough for wearer to sit comfortably).
2 Any life-support system worn on back of user.
backpacker Passenger in cheapest seat(s).
backplane Standard STD or STE bus mounting board
on which computer boards and other modules are
BAD
attached by multiple push-in connectors. Most * accommodate
10 boards and have 20 edge connectors.
backplate Fixed disc behind single-sided centrifugal
compressor.
back porch In electronic display, esp. TV, brief (eg 6 μ)
interval of suppressed video signal at end of each line scan.
back-pressure 1 Pressure in closed fluid system opposing
main flow.
2 Ambient pressure on nozzle of rocket or other jet
engine or any other discharge from fluid system.
backscatter 1 Backward scatter.
2 Signal received by backward scattering.
back-shop In manufacturing plant, first shop to close on
rundown of programme.
backside Moon face turned away from Earth.
backstagger Backward stagger.
backswept Swept.
backswing Linking manoeuvre between tailslide from
zero airspeed with fuselage vertical and start of [upright
or inverted] down-45 line.
backtell Transfer of information from higher to lower
echelon.
backtrack 1 In aircraft operation, to turn through about
180° and follow same track in reverse direction (as
allowance must be made for wind, not same as turn on
reciprocal).
2 Having landed on runway in use, to turn through 180°
and proceed along runway in reverse direction.
back-up 1 Complete programme, hardware item or
human crew funded as insurance against failure of
another.
2 Type of hardware item which could, even with
degraded system performance, replace new design whose
technical success is in doubt.
3 System funded to augment one already in operation
(thus, BUIC).
4 Information printed on reverse of map or other sheet
to supplement marginal information.
backward compatibility The ability of a new or modified
system to operate in old [precursor] system.
backward extrusion Extrusion by die so shaped that
material being worked flows through or around it in
reverse direction to that of die.
backward scatter Electromagnetic energy (eg, radio,
radar or laser) scattered by atmosphere back towards
transmitter. In some cases whole hemisphere facing
towards transmitter is of interest; in radar, attention
usually confined to small amount of energy scattered at
very close to 180° and detected by receiver.
backward stagger Stagger such that the upper wing of a
biplane is mounted further back than the lower.
backward tilt Tilt such that blade tips are to rear of plane
of rotation through centroids of blade roots.
backward wave In a TWT, any wave whose group
velocity is opposite to direction of electron travel.
backwash Slipstream.
BACM Bootstrap air-cycle machine.
BACN Battlefield airborne communications node.
Bacon cell Hydrogen/oxygen fuel cell.
BAC (1/1) Open signal modulation used by Galileo
navsats (EU).
BACS Bleed-air control system.
BAD 1 Boom-avoidance distance; thus * (A) is boom-
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