Definition
A portable or stationary external electrical power source used to supply an aircraft with electrical power while it is on the ground, typically through a connection to the aircraft's external power receptacle. It allows aircraft systems to be operated, and engines to be started, without drawing on the aircraft's own battery.
Plain English
A power cart or trolley that plugs into the airplane on the ground so the airplane can run its electrical systems and start its engine without using its own battery.
Context Anchor
You may see or use a ground power unit during preflight, maintenance, cockpit setup, battery charging, or engine-start procedures on the ramp.
Why Pilots Care
Using a GPU avoids draining the aircraft battery and reduces stress on the starter and engine during ground operations.
Analogy
It is like plugging a device into an outside power source instead of running it only on its internal battery.
Intuition Check
A ground power unit is not power used to move the airplane on the ground. It is electrical power supplied to the airplane while the airplane is on the ground.
Example Sentence 1
Before engine start on a cold morning, the lineman connected a ground power unit to the aircraft so the battery would not be drained during the start.
Example Sentence 2
With no GPU available, the crew performed the preflight on battery power alone.