Definition
Sensing devices that detect and measure changes in velocity (acceleration) along one or more axes. In a Vertical Speed Indicator that uses Instantaneous Vertical Speed Indicator (IVSI) technology, accelerometers sense the initial vertical acceleration of the aircraft when a climb or descent begins, allowing the instrument to display vertical speed almost immediately rather than waiting for the slower pressure-based response.
Plain English
Small sensors that feel changes in motion. In some vertical speed indicators they pick up the moment the airplane starts to climb or descend, so the needle moves right away instead of lagging.
Context Anchor
Seen in discussions of vertical speed indicators, especially systems designed to reduce the normal delay in the instrument indication.
Derivation
From Latin 'accelerare' (to hasten, speed up) plus the suffix '-meter' (a measuring device, from Greek 'metron'). Literally, a 'speed-up measurer' — a device that measures changes in speed.
Why Pilots Care
They remove the several-second lag of a conventional VSI, allowing a pilot to see the start of a climb or descent at once.
Analogy
A phone that knows when it has been tilted or moved uses the same basic idea: a small sensor feels motion changes and turns them into useful information.
Intuition Check
Do not think of accelerometers as measuring only higher speed. They measure changes in motion, including slowing down or changing direction.
Example Sentence 1
The IVSI uses accelerometers to show a climb the instant the pilot pulls back on the controls, rather than waiting for the pressure system to catch up.
Example Sentence 2
During a rapid level-off, the accelerometers in the instrument immediately register the reduction in vertical acceleration.