O&M Operations & maintenance
O2 Oxygen
OAT Outside air temperature
OBIGGS On-board inert gas generating system
oblique wing Wing pivoted at mid-point so that one-half is swept forward, the other half swept backward; aka 'slew wing'
OBOGS On-board oxygen generating system
OBS Omni-bearing selector
also:   On-board simulation
OBST Obstacle
OC Officer commanding
also:   On condition
OCA Obstacle clearance altitude
OCH Obstacle clearance height
OCU Operational conversion unit
also:   Operational capabilities upgrade
OEI One engine inoperative
OEM Original equipment manufacturer
OEU Operational evaluation unit
offset Agreement with a customer nation to contract local workshare; helps to offset purchase costs of aircraft/system aquisition and creates local employment
OG Operations Group (USAF)
OGE Out of ground effect; helicopter hovering performance far above land or water surface
OGMA Oficinas Gerais de Material Aeronautico (Portugal)
OKB Opytno-Kunstruktorskoye Byuro; Russian designation for aircraft or missile design bureau
Omega Long-range radio navigation aid
OMI Omni-bearing magnetic indicator
Opeval Operational evaluation
OPN Open
OPR Operator
OPS Operations
OR Operational requirement (RAF)
OSS Operational Support Squadron (USAF)
OTH Over the horizon
OTHT Over the horizon targeting
OTU Operational training unit
outer marker ILS marker situated on centerline of approach, about 4.5 nm (8.3 km) from runway threshold
OWE Operating weight empty
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Glossary