Definition
Operations performed by digital electronic circuits that produce a specific output based on the combination of input signals, where each input and output is in one of two states (typically represented as 1 or 0, on or off, high or low). The basic logic functions are AND, OR, and NOT, with derived functions including NAND, NOR, and exclusive OR (XOR). These functions form the building blocks of digital computers and microprocessors used in modern avionics.
Plain English
The simple yes/no decisions that a digital circuit makes. Each circuit looks at its inputs (each one either on or off) and produces an output based on a fixed rule. For example, an AND function turns its output on only when all of its inputs are on. Stack enough of these decisions together and you get a computer.
Context Anchor
Seen in avionics, aircraft electrical systems, digital displays, warning systems, and automatic control circuits.
Derivation
From Greek logikē, meaning 'reasoning.' Logic functions are circuits that 'reason' in a strict mathematical way: given specific inputs, they always produce the same predictable output.
Why Pilots Care
These functions control automated decisions in warning systems, flight computers, and sensor logic, so a fault here can trigger false alerts or disable critical automation.
Analogy
A simple logic function is like a rule for turning on a light. For example, the rule might be, “Turn the light on only if both switches are on.”
Intuition Check
Logic functions are not about a person thinking through a problem. Here, they are fixed electronic rules that control what a circuit does with its input signals.
Example Sentence 1
The autopilot's altitude hold uses logic functions to compare the selected altitude with the actual altitude and command the elevator servo accordingly.
Example Sentence 2
Technicians trace a fault to a failed logic function in the engine fire detection circuit that prevented the proper alert from activating.