Definition
An engine-driven pump that uses self-lubricating carbon vanes to move air without internal oil, creating the suction (vacuum) needed to drive gyroscopic flight instruments such as the attitude indicator and heading indicator.
Plain English
A small pump on the engine that sucks air through certain flight instruments to make them work. It is called 'dry' because it doesn't need oil to lubricate its inner parts.
Context Anchor
Seen in aircraft systems, maintenance records, and accident reports involving vacuum-powered flight instruments.
Derivation
Dry' refers to the absence of oil lubrication inside the pump, distinguishing it from earlier 'wet' pumps that used engine oil. 'Vacuum pump' describes its function: it removes air to create a pressure difference (a partial vacuum) that spins the gyros.
Why Pilots Care
Loss of this pump removes attitude and heading information, a common factor in loss-of-control accidents in instrument conditions.
Intuition Check
Do not read “vacuum” as outer-space emptiness here. In this aircraft system, it means suction made by lower air pressure. Do not read “dry air” as weather-related dry air; here, “dry” means the pump is not oil-lubricated inside.
Example Sentence 1
The accident report noted that the dry air vacuum pump had failed shortly before the pilot lost control in cloud.
Example Sentence 2
The NTSB report noted that the dry air vacuum pump had failed, leaving the pilot without reliable attitude reference.