Definition
The component or system in an airplane that produces or supplies electrical power to operate the aircraft's electrical equipment. In most light airplanes, this is an engine-driven alternator or generator, supported by a battery that supplies power when the engine is not running and acts as a backup if the alternator or generator fails.
Plain English
Whatever produces the electricity the airplane needs to run its instruments, lights, radios, and other powered equipment. In small planes this is usually an alternator turned by the engine, with a battery as backup.
Context Anchor
Seen in airplane equipment and lighting discussions, electrical system descriptions, checklists, and the airplane operating handbook.
Derivation
Electrical comes from an old word for amber, a material known long ago for producing static electricity when rubbed. Energy means the ability to do work, and source means the place something comes from. Together, the phrase points to where usable electrical power comes from in the airplane.
Why Pilots Care
If the electrical energy source fails, the pilot is left running on battery power alone, which has limited duration. Knowing where the airplane's electricity comes from helps the pilot recognize a charging-system failure early and load-shed non-essential equipment to preserve battery life.
Analogy
It is like the battery or charger for a phone. The phone may have many features, but they only work while a power source is available.
Intuition Check
Do not read source as only a wall outlet or only a battery. In an airplane, the electrical energy source is whatever approved system is supplying electrical power at that time.
Example Sentence 1
On most single-engine airplanes, the alternator is the primary electrical energy source, and the battery handles starting and backup duties.
Example Sentence 2
With the battery as the only electrical energy source available, the pilot limited electrical loads during the emergency.