Why is the altimeter setting important in METAR/TAF data for runway operations?

• A. Ensures correct vertical separation measurements for en-route navigation only.
• B. Determines weather type recorded.
• C. Ensures correct altitude readings for approaches and altitude separation, affecting minima and vertical guidance reliability.
• D. Only used for calibrating altimeters on the ground.

Answer: (C)

Setting the local altimeter pressure in METAR/TAF is essential to translate atmospheric pressure into accurate altitude readings. For runway operations, precise altitude information is critical during instrument approaches and for maintaining the required vertical separation. The altimeter setting supplied in METAR/TAF (the local QNH) ensures your altimeter reads height above mean sea level correctly, so you can accurately determine your height at key points in an approach, preserve the published minima, and rely on vertical guidance systems like ILS to function as intended. If the setting is incorrect or not updated, your displayed altitude could be too high or too low, which risks undershooting or overshooting minima and can undermine the reliability of vertical guidance. The weather data provide this setting so pilots and air traffic controllers share an accurate, current reference for altitude.