Aviation Glossary - O

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o/r - on request.

o/t - other times.

OAT - outside air temperature. The temperature of the air outside an aircraft measured by a probe with a cockpit gauge readout. OAT affects the measurement of indicated airspeed and its value is needed to calculate true airspeed. At high speeds kinetic heating demands correction to the indicated OAT for true outside air temperature.

OATS - Oxford Air Training School, a large commercial pilot training school at Oxford Airport, UK.

OBS - omni-eighth of the sky is covered.

obst - obstruction.

OCH - obstacle clearance height. The lowest height above the elevation of the runway threshold or above aerodrome elevation used to establish compliance with obstacle clearance criteria in an instrument approach. Also OCA, obstacle clearance altitude, and OCL, obstacle clearance limit.

OCU - Operational Conversion Unit.

OEM - original equipment manufacturer.

okta - a measurement of cloud cover. One okta means one eighth of the sky is covered.

Omega - high accuracy, very-low frequency (VLF) long range navigation system of the hyperbolic type, covering the entire earth down to the surface from eight ground based transmitters. Used principally by airliners, military aircraft and intercontinental business aircraft.

OTU - Operational Training Unit.