O Oscar

obscuration - Any phenomena in the atmosphere, excluding precipitation, that reduces horizontal visibility. According to the National Weather Service, some of the obstructions to visibility include blowing and widespread dust, fog (including freezing fog and patchy fog), haze, mist, sand and blowing sand, smoke, blowing spray, and volcanic ash. It is reported as "X" in an observation and on the METAR.

operations - The takeoffs and landings at an airport.

opposing forces - Forces that are pushing or pulling in the opposite direction. For example, lift is perpendicular to the airflow around an aircraft. If the aircraft is flying straight and level, the lift force (which is pulling up) will be opposing the weight force (which is pulling the aircraft toward the earth).

Oscar - Designator for the letter "O" in the International Phonetic Alphabet.

outages - An interruption in operations as of electrical power.

outer marker - A marker beacon at or near the glideslope intercept altitude of an ILS approach. It is keyed to transmit two dashes per second on a 400 Hz tone, which is received aurally and visually by compatible airborne equipment. The OM is normally located four to seven miles from the runway threshold on the extended centerline of the runway.

outlook briefing - A weather briefing requested by a pilot six or more hours prior to departure, that provides the pilot with weather information pertinent to the proposed flight that serves to help the pilot determine the feasibility of the flight.

over flights - A flight over a given area, especially a flight of military aircraft over foreign territory.

overcast - A weather description for clouds depicting a low ceiling of continuous clouds.

ozone - O3, a triatomic form of oxygen; a pungent, unstable blue gas that in the upper atmosphere forms a protective layer against excess ultraviolet radiation, and is also an ingredient of photochemical smog in the lower atmosphere; it is used in purification of drinking water and as an oxidizing agent. The layer of the upper atmosphere, from about 8 to 30 miles, where most atmospheric ozone is concentrated; it is now regarded as subject to depletion by industrial pollutants, such as fluorocarbons from aerosol sprays.