Definition
An engine-driven air system that spins the gyros inside certain flight instruments — typically the attitude indicator and heading indicator — by moving air through them. A suction (vacuum) system pulls air through the instruments using a vacuum pump, while a pressure system pushes air through them using a pressure pump. Both achieve the same purpose: keeping the gyros turning fast enough to provide accurate attitude and heading information.
Plain English
A system that uses moving air, either sucked or blown by an engine-driven pump, to keep certain cockpit instruments running. If the airflow stops, those instruments stop working correctly.
Context Anchor
Seen in analog instrument failure discussions, especially when checking why an attitude indicator or heading indicator may become unreliable.
Derivation
‘Suction’ comes from Latin sugere, ‘to suck’ — pulling air. ‘Pressure’ comes from Latin pressura, ‘a pressing’ — pushing air. The two words simply describe the two directions air can be moved to drive the same gyros.
Why Pilots Care
Failure removes attitude and heading information, forcing partial-panel techniques or use of backup instruments.
Intuition Check
Do not read “pressure system” here as cabin pressurization, and do not read “suction” as a loose everyday idea. In this context, both refer to controlled airflow used to power specific flight instruments.
Example Sentence 1
During the climb the pilot noticed the suction gauge reading low and suspected a failure of the suction or pressure system.
Example Sentence 2
The pilot checked the suction or pressure system gauge before takeoff to confirm the gyros would operate.