Definition
A flight instrument that displays the rate at which an aircraft state is changing, rather than the current value of that state. Examples include the vertical speed indicator (showing rate of climb or descent in feet per minute) and the turn indicator (showing rate of turn in degrees per second).
Plain English
An instrument that tells you how fast something is changing, not what it is right now. A rate instrument shows movement in progress — how quickly you are climbing, descending, or turning.
Context Anchor
Seen in instrument flying when interpreting the vertical speed indicator during straight-and-level flight, climbs, and descents.
Derivation
Rate comes from the Latin rata, meaning 'a calculated share or measure,' which evolved into the modern sense of 'how much per unit of time.' A rate instrument measures change over time — feet per minute, degrees per second — which is exactly what the word implies.
Why Pilots Care
Enables precise control of climbs, descents, and turns by displaying the speed of change instead of static values.
Analogy
A car speedometer is a rate instrument: it shows how fast your position is changing, not how far you have traveled. The VSI does something similar for altitude.
Grounding Statement
If the instrument answers “how fast is this changing?” it is acting as a rate instrument.
Intuition Check
Do not read “rate instrument” as just “a gauge with a number.” Here, “rate” means change over time, such as feet gained or lost each minute.
Example Sentence 1
The vertical speed indicator is a rate instrument, so it shows how quickly the aircraft is climbing or descending in feet per minute.
Example Sentence 2
Cross-checking the rate instrument with the attitude indicator helped maintain straight-and-level flight in clouds.