Definition
A small, steady electrical current intentionally applied to a component — most often the control grid of an electron tube or the input of a transistor — to set its operating point so that it responds correctly to incoming signals.
Plain English
A small background current that is always flowing through a part of a circuit to keep it ready to work properly when a real signal arrives.
Context Anchor
Seen in aircraft electrical and avionics maintenance, especially when discussing radios, sensors, amplifiers, and other electronic circuits.
Derivation
From the Old French biais, meaning a slant or tilt to one side. In electronics, the bias current 'tilts' the component away from its neutral state into its proper working range.
Why Pilots Care
Pilots rarely adjust bias current directly, but understanding the concept helps when reading avionics troubleshooting notes — a drifting or failed bias current is a common cause of weak radios, distorted audio, or unstable instrument readings.
Intuition Check
Bias does not mean unfair preference here. It means an intentional electrical starting point or offset inside a circuit.
Example Sentence 1
The technician checked the bias current on the radio's amplifier circuit because the audio output had become weak and distorted.
Example Sentence 2
Low bias current in the attitude indicator circuit caused erratic needle movement during the preflight check.