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overall pressure ratio
excluding pitot or instrument probes, static wicks etc). See
length.
overall pressure ratio OPR, ratio of total pressure at
delivery to combustion chamber to that at engine inlet [the
latter taken as unity, so OPR 26:1 can be written as 26]; in
a turbofan OPR = FPR × compressor PR.
overbalanced Provided with excessive balancing mass,
aerodynamic area or other source of control-surface
moment assisting pilot, so that control surface has little
feel (and in extreme case can move by itself to hard-over
deflection).
overboard bleed From compressor to assist starting, not
used in normal running.
overbooking Practice of selling more tickets for a particular
flight than there are seats, to compensate for
(1) no-shows and (2) individual pax or agents making
multiple reservations for one journey.
overbuilt Made stronger than necessary, usually to allow
for future development.
overburn Operation of rocket or other space propulsion
system for too long a period (0.1 s can be significant),
resulting in incorrect cutoff velocity and/or trajectory.
overcast Means 0.9+ cloud cover except IWC = ⅞+
[= 0.875+]. One authority insists “8 oktas”, = 100%.
overcontrol To apply more control deflection than
necessary, commonly resulting in succession of excursions
on each side of desired flight condition.
overdesigned 1 Stronger than necessary to meet requirements.
2 More refined than necessary, usually resulting in
lighter structure at expense of high cost and complexity.
overexpanded nozzle One in which jet leaves at below
ambient pressure.
overfin Fin added above high [T-type] horizontal tail.
overflight Flight over particular route, esp. across
unfriendly territory.
overflight top attack Class of missiles which detonate
shaped charges downwards as they pass over armoured
vehicle.
overfly To fly over.
overhang 1 Spanwise distance from junction of wing and
bracing struts to tip; length of cantilever mainplane.
2 Spanwise distance to tip of upper wing of biplane
from point vertically above tip of lower wing.
3 See next.
overhang balance Mass distributed along leading edge of
control surface, as distinct from horn balance.
overhaul Regularly scheduled procedure of dismantling
(the extent varying with which *), inspection, replacement
of parts if necessary and return to service. For large
aircraft a major * can take weeks and involve refurnishing
and exterior repaint.
overhaul period Also called TBO, the time between
consecutive overhauls. For aircraft or engine or other
functioning item * is actual operating time in hours. For
missile and some other items such as ejection seat it is total
elapsed time.
overhead 1 Apart from normal meanings, involving the
use of one or more satellites.
2 As a noun, a panel for controls and instruments
mounted above the windscreen or in the cockpit roof.
overhead approach Landing procedure in which pilot
flies downwind over point of touchdown and then makes
overshoot
descending circular pattern centred on extended landing
centreline; also called 360° landing.
overhead camshaft In upright cylinder, above the head;
thus, beyond horizontal cylinder, below an inverted
cylinder.
overhead stick Control column pivoted to cockpit roof.
overhead stowage Provision in passenger transport for
hand baggage and other rigid or heavy items to be stowed
in latched bins above seats.
overhead suspension Docked rigid airship hung from
roof of shed.
overhung 1 Cantilevered beyond last point of support,
esp. applied to fan, compressor or turbine stages mounted
at extremity of shaft system beyond nearest bearing.
2 Projecting beyond tip of fixed surface, adjective
normally applied to aileron or elevator.
overlap 1 Percentage of photograph duplicated on next
frame of same film (see lap).
2 See overlap zone.
overlap tell Transfer of information to adjacent airdefence
facility of (normally hostile or unidentified) tracks
in latter’s region.
overlap zone Designated area on each side of boundary
between adjacent tactical air control or defence regions
wherein co-ordination and interaction are required.
overlay Upper (exoatmospheric) layer of layered
defence system (SDI).
overload report Filed by ATC controller when workload
could lead to safety being compromised.
overload response Procedures designed to enable an
inadequate ATC system to handle traffic at peak periods
(UK).
overload weight 1 Alternate MTO weight authorized
only in unusual circumstances.
2 Any takeoff weight exceeding permitted maximum.
overpressure 1 Limiting values reached above and below
normal atmospheric pressure during passage of blast
wave of explosion (nuclear or conventional).
2 Peak positive pressure reached during passage of
boom from supersonic aircraft.
override Facility for bypassing or overcoming normal
limit on command action to obtain exceptional response,
usually in emergency (eg * boost).
override boost Emergency higher boost pressure available
in exceptional circumstances such as overload
takeoff or in combat.
overrun 1 To fail to stop within available landing
distance.
2 Control facility causing camera to continue operating
for preset number of frames or seconds after cutoff of
control.
overrun area Paved area beyond end of runway which
for any reason is not in use; usually marked with herringbone
pattern.
overrun barrier Layer of material beyond end of runway
provided to arrest overrunning aircraft with minimal
damage; PFA is preferred to gravel.
overrunning clutch One allowing driven member (eg helicopter
rotor) to run ahead of drive system.
overseer Common term for software used in managerial
role in large system.
overshoe Externally attached de-icer of pulsatingrubber
mechanical type; also called boot.
overshoot 1 To abandon landing and make fresh
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