Definition
An electrical current that flows in one direction only, at a steady voltage, through a circuit. In aircraft systems, DC is supplied by the battery and by generators or alternators (after rectification) and powers most of the airplane's electrical loads, including avionics, lighting, and engine starting.
Plain English
Electricity that moves through a wire in one direction, the same way a battery delivers power to a flashlight. It does not switch back and forth.
Context Anchor
Seen in airplane electrical system discussions, especially when describing batteries, generators, electrical buses, and equipment powered by DC electricity.
Derivation
The word 'direct' comes from the Latin directus, meaning 'straight' or 'in a straight line.' It describes electricity that flows straight one way through the circuit, without reversing — which is what distinguishes it from alternating current (AC).
Why Pilots Care
Aircraft batteries supply DC power for engine starting, essential instruments, and avionics; understanding it is required for system operation and failure management.
Analogy
DC is like water flowing through a pipe in one direction. The important idea is not the amount of electricity, but the direction of its flow.
Intuition Check
Do not read “direct” as meaning stronger, simpler, or more reliable. In DC, “direct” means the electrical flow stays in one direction.
Example Sentence 1
The airplane's battery supplies 24-volt DC power to start the engine and to run essential avionics if the generator fails.
Example Sentence 2
After alternator failure the aircraft continues on DC battery power until landing.