IAS stands for what term used as a standard atmospheric model?

• A. International Standard Atmosphere
• B. Instrument Air System
• C. Intercooler Air Supply
• D. Instrument Approach System

Answer: (A)

A standard atmospheric model provides a defined reference for how air properties change with altitude so calculations remain consistent across different conditions. The International Standard Atmosphere is the official term for this model, setting sea-level values (temperature around 15°C and pressure about 1013.25 hPa) and a standard rate at which temperature decreases with altitude up to roughly 36,000 feet. With those rules, properties like pressure and density can be predicted at any altitude, which aircraft performance charts, engine data, and instrument calibrations rely on to be comparable and meaningful. The other options describe equipment or systems rather than a reference atmosphere, so they don’t fit as the standard atmospheric model.