Plain English Meaning

A tiny hole made to an exact size so that air flows through it at a specific, predictable rate — not too fast, not too slow.

Full Definition

A small, precisely sized opening built into a pneumatic instrument or system that allows air to escape or enter at a known, controlled rate. In gyroscopic instruments such as the turn coordinator, a calibrated leak meters the airflow that drives or returns from the gyro, ensuring it spins at the correct speed.

Context Anchor

Seen in the pitot-static instrument section when learning how the vertical speed indicator shows or .