Acronyms
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O
| Acronym | Meaning | Source |
| O/R | On Request | |
| OAR | Office of Airspace Regulation | CASA |
| OAT | Outside Air Transport | |
| OAT | Outside Air Temperature | |
| OBS | Observe, Observed, Observation | |
| OBS | Omni Bearing Selector | |
| OBSC | Obscure, Obscured, Obscuring | |
| OBST | Obstacle | |
| OBSTR | Obstruction | |
| OC | Operating Certificate | |
| OCA | Obstacle Clearing Altitude | |
| OCA | Oceanic Control Area | |
| OCC | Occulting (light) | |
| OCH | Obstacle Clearance Height | |
| OCNL | Occasional, Occasionally | |
| OCT | October | |
| OCTA | Outside Control Area | AIS |
| OCTR | Outside Control Zone | |
| OEI | One Engine Inoperative | |
| OEM | Original Equipment Manufacturer | |
| OFZ | Obstacle Free Zone | |
| OHD | Overhead | |
| OHSMS | Occupational Health and Safety Management Systems | |
| OIS | Obstacle Identification Surface | |
| OLC | Office of Legal Counsel | |
| OLD | Office of Legislative Drafting (replaced by OLDP) at the Attorney-General's Department | |
| OLDI | On-line Data Interchange | |
| OLDP | Office of Legislative Drafting and Publishing (previously OLD) at the Attorney-General's Department | |
| OLS | Obstacle Limitation Surface | |
| OM | Operations Manual | |
| OM | Outer Marker | |
| OPA | Opaque, white type of ice formation | |
| OPC | Office of Parliamentary Counsel | |
| OPMET | Operational Meteorological | |
| OPN | Operational Notification Message (message type designator) | |
| OPN | Open, Opening, Opened | |
| OPR | Operator, Operate, Operative, Operating, Operational | |
| OPS | Operations | |
| ORR | Office of Regulation Review (at the Productivity Commission) | |
| ORS | Online Response System - a CASA online form for consultation documents such as DPs, NPRMs, NPCs, draft ACs and draft CAAPs | CASA |
| OSIP | Overhaul and Special Inspections Periods | |
| OT | Other Times | |
| OTAC | Overseas Territories Aviation Circulars - developed by ASSI, a wholly-owned subsidiary of the UK Civil Aviation Authority. ASSI oversees aviation safety in the UK's overseas territories. | Air Safety Support International (UK) |
| OTAR | Overseas Territories Aviation Requirements - developed by ASSI, a wholly-owned subsidiary of the UK Civil Aviation Authority. ASSI oversees aviation safety in the UK's overseas territories. | Air Safety Support International (UK) |
| OTLK | Outlook (used in Sigmet messages for volcanic ash and tropical cyclones) | |
| OTP | On Top | |
| OUBD | Outboard | |
| OVC | Overcast | |
| OW | Over Water |