What instrument would indicate whether the aircraft is stalling?

The Stall Warning System is designed specifically to alert the pilot when the aircraft is approaching a stall condition. This system typically includes a warning light and an audible alert, triggered by the angle of attack reaching a critical threshold where the wings can no longer generate sufficient lift. Therefore, it provides a direct indication that the aircraft is at risk of stalling, allowing the pilot to take corrective action before an actual stall occurs.

While the airspeed indicator can provide clues about the aircraft's performance and whether it is approaching a stall cloud, it does not give a direct stall indication like the stall warning system. The attitude indicator shows the aircraft's orientation relative to the horizon, which is essential for coordinated flight and for assessing the flight path but does not indicate stall conditions. The vertical speed indicator, on the other hand, measures the rate of climb or descent but has no relevance to stall warnings.

Understanding that the Stall Warning System is tailored specifically for this purpose helps pilots to recognize its importance in maintaining safe operations, particularly in flight maneuvers where stalls are more likely to occur.