Definition
An engine-driven pump that removes air from the instrument system to create suction, which spins the gyros inside air-driven flight instruments such as the attitude indicator and heading indicator.
Plain English
A pump on the engine that sucks air through certain flight instruments to keep their internal spinning wheels turning. Those spinning wheels are what make the instruments work.
Context Anchor
Seen in instrument flying when discussing pneumatic system failure, especially in aircraft that use suction-powered flight instruments.
Derivation
Vacuum comes from the Latin vacuus, meaning empty. The pump doesn't create a true emptiness, but it lowers the air pressure inside the system enough that outside air rushes in to fill the gap, and that moving air is what spins the gyros.
Why Pilots Care
Failure disables the attitude indicator and heading indicator, forcing immediate use of partial panel procedures or backup instruments.
Analogy
It is like using a straw to create suction. You are not making a perfect empty space; you are lowering the pressure so air wants to move through the straw.
Intuition Check
A vacuum pump does not create a perfect vacuum. In this aircraft system, it creates enough suction to run certain instruments.
Example Sentence 1
When the vacuum pump failed in cruise, the attitude indicator slowly tilted off true and the pilot transitioned to partial-panel flying.
Example Sentence 2
A sudden loss of vacuum pressure warned that the vacuum pump might have failed.