Organization of American States Offensive Air Support Office of Applied Studies Offensive Avionics System Obstacle assessment surface Office of Aircraft Services Old Age Security One-to-All Scatter Option Adjusted Spread Office Automation System Office of Administrative Services Open Application Server Orbiter Aeroflight Simulator Orbiter Atmospheric Simulator Orbiter Avionics System Organisation of American States Obstacle Assessment Surfaces Office of the Assistant Secretary Online Assessment System Operational Areas Operations Applications optical alignment sights Oracle Application Server Orbit Analysis System Orbital Analysis System Orbiter Attachment System O-acetyl-L-serine O-acetylserine oceanic automation system Offensive Avionics Suite