Definition
An electrical current in which the flow of electrons reverses direction at a regular rate, typically expressed in cycles per second (hertz). In aircraft electrical systems, AC is generated by alternators or inverters and is used to power equipment such as instruments, avionics, and certain motors that require alternating current to operate.
Plain English
Electricity that rapidly switches direction back and forth instead of flowing one way. It is the kind of power that runs many of the airplane's instruments and avionics.
Context Anchor
Seen in airplane electrical system descriptions, especially when comparing what different generators, alternators, buses, or pieces of equipment need for power.
Derivation
From Latin alternare, meaning 'to do by turns,' and the everyday word current, meaning the flow of electricity. The name simply describes what the electricity does: it takes turns flowing one way, then the other.
Why Pilots Care
Aircraft systems such as avionics, lights, and instruments depend on stable AC power; failure to understand the distinction from direct current can delay troubleshooting of electrical faults.
Analogy
Think of AC like a person pushing a swing back and forth. The motion keeps reversing direction, but energy is still being delivered.
Intuition Check
AC does not mean air conditioning in this electrical-systems context. Here, AC means alternating current: a type of electrical power that repeatedly reverses direction.
Example Sentence 1
The turboprop's engine-driven generator supplies AC power to the flight instruments and avionics.
Example Sentence 2
During the preflight, the crew verified that the AC electrical system showed normal voltage output.