Definition
Direct current is electrical current that flows steadily in one direction through a circuit, at a constant voltage polarity. In aircraft, it is the form of electrical power supplied by the battery and, in most light aircraft, by the alternator or generator after rectification. DC powers the majority of onboard electrical systems including lighting, avionics, starter motors, and instruments.
Plain English
Electricity that flows one way only, like water moving steadily through a pipe in a single direction. It comes from the battery and powers most of the airplane's electrical equipment.
Context Anchor
Seen in aircraft electrical system discussions, especially when describing batteries, generators, alternators, and 14- or 28-volt aircraft power.
Derivation
From Latin directus meaning 'straight' or 'in a straight line.' The current moves in one direction only, as opposed to alternating current (AC), which reverses direction many times per second.
Why Pilots Care
Aircraft batteries and rectified alternator output deliver DC power to instruments, radios, and flight controls; loss of DC can disable critical systems.
Analogy
DC is like traffic on a one-way street: the flow keeps moving in one direction. That is different from a street where traffic direction keeps switching back and forth.
Intuition Check
Direct does not mean “shortest route” here. It means the electrical flow keeps the same direction through the circuit.
Example Sentence 1
The aircraft battery supplies 24-volt direct current to the starter motor during engine start.
Example Sentence 2
The alternator produces alternating current that is converted to direct current before reaching the avionics.