Which statement about flight instruments is true?

The statement regarding the heading indicator being a gyroscopic instrument that must be aligned with the magnetic compass is accurate. The heading indicator, or directional gyro, relies on gyroscopic principles to maintain its orientation and provides a stable reference for the pilot to determine the current heading. However, it needs to be periodically aligned with the magnetic compass to account for the precession of the gyro and any drift that might occur over time. This alignment is essential for ensuring accurate navigation, as the magnetic compass provides a reference to the Earth's magnetic field, while the heading indicator can be affected by various factors during flight.

In contrast, the other statements describe functions unrelated to the particular instruments. The altimeter measures altitude based on atmospheric pressure, not airspeed. The airspeed indicator specifically measures the dynamic pressure, which indicates the speed of the aircraft through the air, rather than providing altitude information. The vertical speed indicator tracks the rate of climb or descent by comparing pressure changes in the static system but does not use pitot static pressure directly; it reflects changes in static pressure over time.