Plain English Meaning

A small pump turned by the engine that moves air through the system that spins certain flight instruments. It uses spinning blades that slide in and out to push the air along.

Full Definition

A mechanical air pump mounted on and driven by the aircraft engine, using a rotor with sliding vanes inside an offset chamber to produce the suction or pressure airflow that powers air-driven gyroscopic instruments. As the rotor turns, the vanes slide in and out to maintain contact with the chamber wall, drawing air in on one side and expelling it on the other. It has replaced the older venturi system in most modern aircraft because it works on the ground and at all airspeeds.