Definition
A cockpit instrument that displays the amount of suction (negative pressure) being produced by the aircraft's vacuum system, typically measured in inches of mercury (in. Hg). The vacuum system drives the air-driven gyroscopic instruments such as the attitude indicator and heading indicator, and the gauge confirms that suction is within the manufacturer's specified operating range.
Plain English
A small dial in the cockpit that shows whether the suction powering some of the spinning instruments is at the right strength. If the reading is too low or too high, those instruments may not be reliable.
Context Anchor
Seen during the instrument check before flight, especially in aircraft with vacuum-driven attitude or heading instruments.
Derivation
Vacuum' comes from the Latin vacuus, meaning 'empty.' A 'gauge' is simply a measuring device. Together, the term describes an instrument that measures how much the system has emptied (reduced) the air pressure to create suction.
Why Pilots Care
Confirms the gyroscopic instruments receive enough suction to remain reliable; low or zero readings indicate potential pump or system failure before flight.
Grounding Statement
A healthy vacuum gauge reading means the system is pulling enough air through the instruments to keep their internal spinning parts working correctly.
Intuition Check
Vacuum does not mean outer space or a completely empty chamber here. It means suction created by lower air pressure in the aircraft’s instrument system.
Example Sentence 1
During the runup, the pilot checked the vacuum gauge and confirmed the suction was within the green arc before departing.
Example Sentence 2
A dropping vacuum gauge reading in flight prompted the pilot to cross-check the attitude indicator against the turn coordinator.