How does the Vertical Speed Indicator (VSI) determine altitude changes?

The correct method by which the Vertical Speed Indicator (VSI) determines altitude changes is through a calibrated leak in the case. The VSI operates by comparing the static pressure inside the instrument with the static pressure outside the instrument case. When there is a change in altitude, the external static pressure changes more quickly than the pressure inside the VSI, thanks to the calibrated leak. This pressure differential is used to indicate whether the aircraft is climbing or descending and at what rate, resulting in the vertical speed reading.

The other choices do not accurately describe how the VSI functions. While the pitot tube measures dynamic air pressure for airspeed indicators, this information does not help in determining altitude changes. A barometric sensor compares ambient atmospheric pressure but is not the mechanism used in a traditional VSI. GPS altitude data, while useful for determining altitude, does not play a role in the functioning of a conventional VSI. Such systems typically rely on mechanical pressure measurement rather than electronic or satellite-based methods.