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occulting Flashing, but with illuminated periods clearly
predominant.
OCD 1 Operational concept demonstration.
2 Oceanic clearance delivery.
3 Office of Civilian Defense (US, 1941).
4 On-chip debug.
oceanic airspace Controlled airspace over ocean areas.
oceanic clearance Clearance delivery to enter oceanic
airspace.
oceanic navigation error report Filed when surveillance
monitor observes aircraft exiting oceanic airspace seriously
off track.
ocean spatial spectrum Readout of the topography of
the oceanic surface, measured by a WSOA.
OCF 1 Occluded frontal passage.
2 Operational Conversion Flight (RAF).
OCFNT Operational Conversion Flight (RAF).
Occluded front.
OCH Obstacle clearance height.
OCI 1 Outside of clearance indicator (MLS).
2 Out-of-coverage indicator (navaids).
OCIG Oceanic communications improvement group.
OCIP Offensive capability improvement program.
OCL 1 Obstacle [or obstruction] clearance limit.
2 Optimum cruising level.
OCLD Occlude.
OC level Height [usually in thousands of feet a.m.s.l.] of
overcast.
OCLN Occlusion.
OCM 1 On-condition maintenance.
2 Optical countermeasures.
3 Optimal control model.
4 Organizational control manual.
OCNL Occasional [OCNLY, occasionally].
OCNR Office of the Chief of Naval Research (USN).
Oconus Offshore, or outside, the US.
OCP 1 Onmnidirectional control pattern.
2 Oceanic clearance processor.
OCR 1 Optical-character recognition, or reading.
2 Oceanic control region.
3 On-condition replacement.
4 Office of Commitments and Requirements.
5 Occur.
OCS 1 Optimum-cost speed.
2 Officer Candidate School (US).
3 Oceanic Control System (NZ).
4 Obstacle clearance surface.
5 Operational control segment.
6 Officers Command School (RAF Henlow).
oct Octane (FAA).
octa Unit of visible sky area representing one-eighth of
total area visible to celestial horizon, now okta.
Octagon Trade-name of a range of de-icing fluids,
including potassium and sodium acetates, sodium
formate and propylene glycol.
octal 1 Standard base for electronic device having eight
connector pins.
2 Counting system to base 8.
octane number Standard system for expressing
resistance of hydrocarbon or other fuel to detonation in
piston engine, ranging from 0 (equivalent to n-heptane)
through 100 (iso-octane) upwards to about 150. Measures
are taken with lean mixture and with rich, latter giving
higher values. Also called knock rating (strictly, antiobstruction
clearance surface
joining highest point of object in flightway [ie, approach
path] to nearest point of appropriate runway.
obstruction clearance surface Surface in form of plane or
flat cone sloping at obstruction angle.
obstruction-free zone Free from all fixed obstacles
except light frangibly mounted navaids.
obstruction light Red light visible 360° on top of object
dangerous to moving aircraft in air or on ground.
obstruction marker Object of approved shape or colour
marking obstruction or boundary of hazardous surface
on airfield.
OBT Off-block[s] time.
OBTD On-board training device.
Obtex Off-board targeting experiment[s].
obturator Rigid or flexible body tailored to preventing
escape of gas under pressure from particular orifice or
other leakage path.
obturator ring Piston ring of L-section intended to be
gastight.
OBW 1 On-board wheelchair (for disabled pax).
2 Off-boresight weapon.
OC, O/C 1 O’clock.
2 Officer commanding.
3 Over-current.
4 Obstacle clearance (ICAO panel).
5 Optical communications.
6 Obstruction chart.
7 Officer candidate.
8 Oil consumption.
9 On course.
10 Operational conversion, see OCF, OCU.
11 Overcast.
12 Operational Clearance [followed by number 1 or 2].
OCA 1 Obstacle clearance altitude [suffix H fm , height
for finals and straight missed approach; H ps , height for
precision segment].
2 Oceanic control area.
3 Offensive counter-air.
4 Old Cranwellians Association.
5 Oil-cooler augmentation.
OCALC Oklahoma City Air Logistics Center (Tinker
AFB).
OCAMS, Ocams On-board checkout and monitoring
system.
OCC 1 Operation[s] [or Oceanic] control centre.
2 Occulting.
3 Occupied [telephone line].
4 Operator control console.
Occar Organisme Conjointe de Co-opération en
Matière d’Armément (Int.).
occluded front Warm air mass forced aloft by overtaking
cold front.
occlusion 1 Atmospheric region in which cold front has
overtaken slow or stationary warm front and forced warm
air mass upwards.
2 Trapping of gas bubbles in solidifying material or by
molecular adhesion on surface, esp. removal of gas in
high-vacuum technology by a getter.
OCCM Optical counter-countermeasures.
OCCS Operations control-center software.
occultation Complete disappearance of body, esp.
source of illumination such as star or aircraft lights,
behind another object of much larger apparent size.
octane number
460