Definition
The component or system that produces the suction (lower-than-ambient pressure) needed to drive air-powered gyroscopic flight instruments such as the attitude indicator and heading indicator. Common vacuum sources include an engine-driven vacuum pump, a venturi tube mounted in the slipstream, or, in some installations, a pressure pump that supplies pressurized air rather than suction.
Plain English
It is whatever the airplane uses to suck air through certain flight instruments so the spinning gyros inside them keep turning. Without it, those instruments stop working properly.
Context Anchor
Seen in discussions of pneumatic systems, vacuum-driven gyroscopic instruments, and instrument failure checks.
Derivation
Vacuum comes from the Latin vacuus, meaning 'empty.' In aviation it does not mean a true empty space — it means air pressure that has been reduced below the surrounding air, so outside air rushes in to fill the gap. That moving air is what spins the gyros.
Why Pilots Care
A failed vacuum source leaves the pilot without reliable attitude and heading information in clouds or at night.
Intuition Check
Do not think of a vacuum source as creating a perfect empty space. In this context, it creates a pressure difference that makes air flow through the instruments.
Example Sentence 1
During the runup, the pilot checked the suction gauge to confirm the vacuum source was producing normal pressure for the gyro instruments.
Example Sentence 2
Before flying into instrument conditions the crew confirmed the vacuum source was producing normal pressure.