ASI and DASI are instruments used to measure what at a terminal facility?

• A. Air pressure
• B. Humidity
• C. Temperature
• D. Wind speed

Answer: (A)

The main idea is that these instruments operate based on air pressure differences. An air speed indicator uses the pressure of moving air (dynamic pressure) via a pitot tube and compares it to the ambient static pressure, while a differential air speed indicator uses pressure differences to derive its reading. Because both rely on sensing air pressure to produce their indications, they are measuring air pressure in the environment at the terminal facility. Humidity and temperature are detected by different sensors, and wind speed is measured with an anemometer, not these pressure-based devices. So air pressure is the correct measurement.