O
- o-ring
- observation balloon
- obstacle
- obstacle-free zone
- obstacle identification surface
- obstacle light
- obstacle limitation surface
- obstacle/terrain data collection surface
- octane rating
- octant
- ohm
- oil-pressure gauge
- oil pressure indicator
- oil temperature indicator
- omnidirectional beacon
- omnidirectional radio beacon
- on-scene
- on-the-job training
- one stop security
- open fracture
- open skies agreement
- opening time
- operating time
- operating weight
- operational ceiling
- operational control
- operational flight plan
- operational incident
- operational planning
- operational wind shear warning system
- operations manual
- operator
- operator’s maintenance control manual
- opposed-piston engine
- optimal search area
- original equipment manufacturer
- ornithopter
- orographic cloud
- orographic rain
- orographic thunderstorm
- orographic turbulence
- orthometric height
- oscar
- out of ground effect
- outboard
- outbound leg
- outer main gear wheel span
- outer marker
- outflow valve
- outside air temperature
- overbooking
- overcast
- overdue
- overflight
- overhaul
- overpack