Definition
On a vertical speed indicator (VSI), the trend indication is the immediate movement of the needle that shows whether the aircraft is beginning to climb or descend, and how quickly that change is occurring, before the instrument settles on the actual rate of climb or descent.
Plain English
It is the early movement of the VSI needle that tells the pilot a climb or descent is starting, and roughly how strongly, before the instrument shows the steady, accurate rate.
Context Anchor
Seen when using the vertical speed indicator during climbs, descents, and level-offs in instrument flying.
Derivation
Trend comes from an old word meaning to turn or roll in a direction. In flight instruments, it captures the idea of a needle starting to swing toward a new value, showing the direction the aircraft's vertical motion is heading before the final number arrives.
Why Pilots Care
Gives an immediate heads-up on altitude changes so the pilot can correct before the situation grows larger.
Intuition Check
Do not read trend indication as a perfectly exact number. It is mainly showing the direction of change first; the exact rate may take a moment to settle.
Example Sentence 1
As she lowered the nose slightly, the trend indication on the VSI showed an immediate downward movement before settling on a 500 foot-per-minute descent.
Example Sentence 2
During the climb, the trend indication showed an immediate nose-up movement even though the rate needle had not yet settled.