Which instrument can function as a navigational aid by providing heading information?

The heading indicator is the instrument that provides critical heading information for navigation. This tool is essential for pilots as it displays the aircraft's current magnetic heading, allowing them to maintain a specific course during flight. It is especially useful in poor visibility conditions, where a visual reference may be limited.

In contrast, while the airspeed indicator measures how fast the aircraft is moving through the air, it does not provide directional information. The altimeter measures altitude, which is vital for maintaining proper flight levels but does not indicate the direction of travel. The clock, while important for timing purposes and managing flight durations, does not serve any navigational function in terms of providing heading information. Thus, the heading indicator is key for navigation as it ensures pilots can navigate accurately by maintaining a specific heading.