A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

OACOceanic area control centre
OASObstacle assessment surface
OATOperational air traffic
OBSObserve or observed or observation
OBSCObscure or obscured or obscuring
OBSTObstacle
OCAObstacle clearance altitude
OCAOceanic control area
OCHObstacle clearance height
OCLObstacle clearance limit
OCNLOccasional or occasionally
OCSObstacle clearance surface
OCTOctober
OFZObstacle free zone
OHDOverhead
OLDIOn‚ąíline data interchange
OMOuter marker
OPAOpaque, white type of ice formation
OPCThe control indicated is operational control
OPMETOperational meteorological (information)
OPNOpen or opening or opened
OPROperator or operate or operative or operating or operational
OPSOperations
O/ROn request
OTLKOutlook (used in SIGMET messages for volcanic ash and tropical cyclones)
OTPOn top
OTSOrganized track system
OUBDOutbound
OVCOvercast
(C) 2012-18 Jan Hrkal