Definition
The systems on an aircraft that supply the moving air used to spin air-driven gyroscopic instruments. The two common arrangements are a vacuum (suction) system, which pulls air through the instrument by means of an engine-driven vacuum pump or a venturi, and a pressure system, which pushes air through the instrument from an engine-driven pressure pump. The moving airflow strikes small buckets on the gyro rotor and spins it at high speed.
Plain English
These are the parts of the aircraft that produce the airflow needed to spin the gyros inside certain flight instruments. Some aircraft suck the air through; others blow the air through. Either way, the moving air is what keeps the gyros turning.
Context Anchor
Seen in instrument-system discussions when explaining how some gyroscopic instruments are powered instead of using electricity.
Derivation
Pneumatic comes from the Greek pneuma, meaning breath or air. In aviation, anything called pneumatic is powered by moving air, which fits exactly: these systems run the gyros using airflow rather than electricity.
Why Pilots Care
The attitude indicator and heading indicator on many aircraft depend on these systems. If the pneumatic source fails, those instruments slowly run down and give misleading readings, which is especially dangerous in instrument flying. Knowing whether the aircraft uses vacuum or pressure, and how to check it, is part of safe IFR operation.
Grounding Statement
Air moving through the instrument spins the gyro at high speed so the instrument can sense changes in aircraft attitude.
Intuition Check
Pneumatic does not mean only tires or brakes here. In this context, it means airflow used as a power source for flight instruments.
Example Sentence 1
Before takeoff, the pilot checked the suction gauge to confirm the pneumatic source was producing enough airflow to drive the attitude indicator.
Example Sentence 2
During preflight the pilot checks that the suction gauge shows adequate pressure from the pneumatic sources before relying on the gyro instruments in instrument conditions.