| Company | Search On | Records | Category | Sub category |
| Oxford Air Training School |
OATS |
120 | Training | Classroom |
| O-Cedar Ltd | OCedar | 1 | Chemicals | Cleaning Agent |
| Oddie Bradbury & Cull Ltd | Oddie | 19 | Fasteners | Panels |
| Oddy & Co. W.D. | Oddy | 9 | Components | Propellers |
| Oerliken Machine Tool Works | Oerliken | 1 | Weapons | Armaments |
| Oil Engines (Coventry) Ltd | OilEngines | 5 | Maintenance | Stationary Engines |
| OK Supreme | OKSupreme | 1 | Aeronautical Engineers | |
| Old Bleach Linen Co Ltd. The | OldBleach | 1 | Materials | Fabrics |
| Oldham & Son Ltd | Oldham | 39 | Components | Batteries |
| Olley Air Services Ltd | Olley | 1 | Air Transport | Airlines |
| Olympic Airways | OlympicAirways | 2 | Air Transport | Airlines |
| Omes Ltd | Omes | 17 | Manufacturing | Forging |
| Omnipol | Omnipol | 94 | Aircraft Manufacturers | Non UK |
| Omnium Central | Omnium | 6 | Suppliers | Spare Parts |
| Optical Measuring Tools Ltd | OpticalTools | 3 | Engineering Equipment | Test Equipment |
| Orbit Motors Ltd | OrbitMotors | 1 | Components | Pumps |
| Orcene Products Ltd | Orcene | 1 | Chemicals | Cleaning Agents |
| ORD Engineering Co |
ORD | 2 | Fabrication | Sheet Metal Work |
| Orenda Engines Ltd |
Orenda |
27 | Engine Manufacturers | Non UK |
| Organisations (Misc) | Organisations | 5 | Organisations | Professional |
| Oriental Tube Co Ltd | OrientalTube | 5 | Manufacturing | Tubing |
| Ormerod Engineers Ltd | Ormerod | 1 | Manufacturing | Turned Parts |
| Ormond Engineering Co Ltd | Ormond | 3 | Manufacturing | Machining |
| Osborne Aircraft Components Ltd | OsborneAircraft | 1 | Aircraft | Engineering |
| Otter Controls Ltd | OtterControls | 2 | Components | Controls |
| Oval School Of Flying | OvalSchool | 3 | Training | Flying School |
| Overhaul Activities Overhaul Services Ltd | OverhaulActivities | 1 | Engineering | Maintenance |
| Overseas Aviation (C.I.) Ltd | OverseasAviation | 1 | Air Transport | Airlines |
| Owen Bros & Co Ltd | OwenBros | 1 | Finishes | Paints |
| Owen Davies Engineering Co Ltd | OwenDavies | 1 | Manufacturing | Sheet Metal Work |
| Owen Organisation. The | OwenOrganisation | 1 | Manufacturing | Components |
| Oxford Aviation |
OxfordAviation | 0 |
Aircraft Sales | |
| Oxley Developments Ltd | OxleyDevelopments | 1 | Components | Electronics |
| Oyler & Co Ltd | Oyler | 3 | Components | Seating |
| Ozalid Company Ltd | Ozalid | 1 | Engineering Equipment | Drafting |
