Definition
Vertical Speed Indicators that incorporate accelerometer-driven pumps to sense vertical acceleration at the moment a climb or descent begins, eliminating the 6-to-9-second lag found in conventional VSIs and displaying the rate of climb or descent almost immediately.
Plain English
A type of vertical speed indicator that shows how fast you are climbing or descending right away, instead of taking several seconds to catch up like older versions.
Context Anchor
Seen on instrument displays and VSI tapes when learning to hold straight-and-level flight, climb, descend, or level off smoothly.
Derivation
Instantaneous comes from the Latin instans, meaning 'at this moment.' The name describes what sets these instruments apart: they respond at the moment vertical motion begins, rather than after a delay.
Why Pilots Care
Enables quicker detection and correction of unintended altitude changes, improving precision and safety in instrument conditions.
Intuition Check
Instantaneous does not mean perfectly delay-free here. It means the VSI responds much faster than a standard VSI, so the pilot sees the climb or descent trend sooner.
Example Sentence 1
Because the aircraft was equipped with instantaneous VSIs, the pilot saw the descent rate develop the moment she lowered the nose.
Example Sentence 2
During turbulence, the instantaneous VSIs helped the pilot make small pitch corrections before altitude deviations grew large.