O
- observation balloon
- observational network
- obstacle
- obstacle-free zone
- obstacle clearance surface
- obstacle free zone
- obstacle identification surface
- obstacle light
- obstacle limitation surface
- obstacle protection surface
- octant
- off-airport landing
- oil control valve
- oil cooler
- oil dilution system
- oil filter
- oil pan
- oil radiator
- oil resistance
- omnidirectional beacon
- on-condition maintenance
- on-scene
- on-the-job training
- one stop security
- open-water winching
- open fracture
- open skies agreement
- opening
- operating characteristic
- operating empty weight
- operating Mach number
- operating time
- operating weight
- operational accident
- operational ceiling
- operational check
- operational control
- operational incident
- operational personnel
- operational readiness
- operational wind shear warning system
- operations specifications
- operator
- operator of aircraft
- optimal search area
- optimum visibility and surface conditions
- ornithopter
- orographic cloud
- orographic rain
- orographic thunderstorm
- orographic turbulence
- orthometric height
- orthotropic
- oscar
- oscillator
- oscillatory spin
- out of ground effect
- out of ground effect hover
- outboard
- outbound leg
- outer cover
- outer marker
- outer marker beacon
- outer packaging
- outer ridge-girder
- outside air temperature
- outward relief valve
- over-run excursion
- overbooking
- overcast
- overdue
- overflight
- overflow groove
- overhang
- overhaul
- overlay sheet
- overload
- overpack
- overpressure height
- overrun excursion
- overshoot
- overspeed condition
- overtemperature
- overthrow straps
- overtorque
- oxigen meter
- oxygen