Definition
A trim setting in which the elevator trim tab is adjusted so that the airplane's natural tendency, with the control yoke released, is to pitch the nose downward. It relieves the pilot of having to hold forward pressure on the controls to maintain a lower pitch attitude.
Plain English
The airplane is set up so that, hands off, the nose wants to drop rather than climb. The pilot doesn't have to keep pushing the controls forward to hold that attitude.
Context Anchor
Used in pitch control, especially when the pilot needs to reduce a climb, begin or hold a descent, or manage the airplane after a problem with the normal up-and-down control.
Derivation
Trim comes from old sailing use, where it meant arranging sails so a boat was balanced and handled properly. In aviation, trim has the same basic idea: adjusting the airplane so it stays balanced with less force from the pilot.
Why Pilots Care
In an elevator-control emergency, proper nose-down trim helps the pilot maintain a stable descent and safe airspeed with minimal control input.
Intuition Check
Do not think of trim as a command that instantly points the nose down. Nose-down trim changes the airplane’s balance so it tends to lower the nose or need less force to keep the nose down.
Example Sentence 1
After leveling off from the climb, he rolled in a touch of nose-down trim so the airplane would hold cruise pitch without constant forward pressure.
Example Sentence 2
Applying a small amount of nose-down trim reduced the forward yoke pressure needed after the simulated elevator failure.