What does an airspeed indicator display?

The airspeed indicator displays the aircraft's speed relative to the surrounding air, which is crucial for various aspects of flight performance, including lift, drag, and overall aircraft control. This speed, referred to as indicated airspeed (IAS), is displayed in knots and is essential for safe takeoff and landing as well as for maintaining proper flight attitudes during maneuvers.

Understanding this concept is fundamental to piloting, as it helps the pilot make informed decisions regarding aircraft performance and safety. For instance, if a pilot knows their speed is too low, they can take corrective action to avoid stalling. The indicator uses the principles of pressure differential to measure airspeed by comparing the dynamic pressure of the air impacting the aircraft with the static pressure surrounding it.

The other options focus on unrelated metrics. Altitude is assessed using altimeters, distance to an airport is typically calculated using navigation systems, and wind speed is measured with an anemometer or inferred through weather data, rather than being displayed on an airspeed indicator. Hence, the correct understanding is that the airspeed indicator specifically relates to the aircraft's speed through the air.