Definition
A vertical speed indicator that uses an internal accelerometer-driven pump (called a dashpot or vane pump) to sense the start of a climb or descent the moment it begins, eliminating the lag found in a conventional VSI. It still displays the rate of climb or descent in feet per minute, but it responds to pitch changes almost immediately rather than after several seconds.
Plain English
A climb-and-descent gauge that reacts right away when you start going up or down, instead of taking a few seconds to catch up like a normal one.
Context Anchor
Seen in cockpit instrument panels, especially in instrument flying, climb control, descent planning, and altitude changes where quick vertical movement information matters.
Derivation
Instantaneous comes from Latin instans, meaning at this very moment. The name highlights what makes this instrument different from a standard VSI: it responds at the moment a vertical change begins, not after a delay.
Why Pilots Care
Gives immediate feedback during climbs, descents, and instrument approaches so pilots can make precise corrections without overshooting altitude targets.
Analogy
A standard vertical speed indicator can feel like a scale that takes a moment to settle after you step on it. An Instantaneous Vertical Speed Indicator is more like a scale that reacts almost right away, so you see the change sooner.
Grounding Statement
Pressure changes from climbing or descending reach the instrument almost at once, so the needle moves without hesitation.
Intuition Check
“Instantaneous” does not mean the instrument is perfect or has absolutely zero delay. It means it is designed to remove most of the normal delay so the vertical speed indication appears much sooner.
Example Sentence 1
When she lowered the nose slightly, the instantaneous vertical speed indicator showed a 200-foot-per-minute descent right away, instead of the usual delay.
Example Sentence 2
On the ILS approach the Instantaneous Vertical Speed Indicator showed the exact descent rate needed to stay on the glide path.