Definition
An altimeter inaccuracy caused by the static ports sensing slightly higher or lower air pressure than the true ambient pressure when the aircraft is pitched up or down. Because the static system is sensitive to the angle at which air strikes the static ports, changes in pitch attitude can momentarily distort the pressure reading and produce a small altitude error on the altimeter.
Plain English
A small altimeter reading error that shows up when the nose is pitched up or down, because the airflow over the static ports changes and feeds the altimeter a slightly off pressure.
Context Anchor
Encountered when using the altimeter to help hold altitude during straight-and-level instrument flight.
Derivation
Pitch' here means the nose-up or nose-down angle of the aircraft, from the old idea of something tipping forward or back. 'Error' simply means a deviation from the true value. Together: an error caused by the aircraft's pitch attitude.
Why Pilots Care
During steep climbs, descents, or rapid pitch changes, the altimeter may briefly indicate an altitude that isn't quite right. Knowing this prevents chasing a momentarily false reading and helps the pilot trust the instrument once the aircraft is stabilized.
Intuition Check
Do not read pitch error as an altimeter malfunction. In this context, it means the airplane’s nose attitude is wrong for level flight, and the altimeter is showing the result.
Example Sentence 1
After leveling off from a steep climb, the instructor pointed out that the altimeter settled by a few feet as the pitch error worked itself out.
Example Sentence 2
Maintaining a constant pitch attitude minimizes pitch error and keeps the altimeter reliable during instrument flight.