Definition
On the vertical speed indicator (VSI), a stable indication is a steady, unchanging reading that accurately reflects the aircraft's current rate of climb or descent in feet per minute, occurring after the brief lag period required for the instrument to settle following a pitch change.
Plain English
It's when the VSI needle stops moving and holds still on a single number, showing the true rate at which the aircraft is climbing or descending.
Context Anchor
Seen when interpreting the vertical speed indicator during straight-and-level flight, climbs, and descents.
Derivation
Stable comes from a Latin word meaning “standing firm.” Indication comes from a Latin word meaning “to point out.” Together, the phrase points to a reading that is firm enough to rely on, not one that is still settling.
Why Pilots Care
Confirms the aircraft has settled at a steady vertical speed so the pilot can trim or adjust pitch without overcorrecting.
Intuition Check
Stable does not mean the aircraft is perfectly safe or that the reading will never change. Here, it means the displayed reading has settled enough to be useful.
Example Sentence 1
After leveling off at 6,000 feet, the pilot waited a few seconds for a stable indication on the VSI before fine-tuning the pitch attitude.
Example Sentence 2
The VSI gave a stable indication of 400 feet per minute climb once the power and attitude were set.