Definition
A change in the rate at which the aircraft's nose is pitching up or down. In the context of the vertical speed indicator (VSI), pitch acceleration produces a momentary lag or overshoot in the indicated vertical speed because the instrument senses the rate of pressure change rather than instantaneous altitude change.
Plain English
How quickly the nose is changing its up-or-down movement. If you abruptly raise or lower the nose, that is pitch acceleration, and the VSI will not show your true climb or descent rate until the air pressure inside the instrument catches up.
Context Anchor
Seen when learning why the Vertical Speed Indicator can momentarily lag, lead, or fluctuate during pitch changes.
Derivation
Pitch refers to nose-up or nose-down rotation of the aircraft around its lateral axis. Acceleration, from the Latin accelerare meaning 'to hasten,' refers to a change in rate. Together: a change in the rate of nose-up or nose-down motion.
Why Pilots Care
Allows the VSI to show an initial climb or descent instantly, helping pilots recognize the start of a maneuver without waiting for the instrument to catch up.
Grounding Statement
If you raise or lower the nose quickly, the airplane’s vertical motion changes for a moment before it becomes steady.
Intuition Check
Do not read “pitch” here as propeller blade angle or as throwing something. Here it means the airplane’s nose-up or nose-down motion. Also, “acceleration” does not only mean gaining forward speed; it means a change in motion.
Example Sentence 1
The instructor demonstrated how a sudden pitch acceleration causes the VSI needle to overshoot before settling on the actual climb rate.
Example Sentence 2
The pilot watched the VSI needle jump due to pitch acceleration even before the airplane began a steady climb.