Definition
A type of digital logic circuit whose output depends only on the present combination of its inputs, with no memory of previous input states. The output changes immediately when the inputs change, following a fixed set of logic rules built from gates such as AND, OR, and NOT.
Plain English
A circuit that gives an output based purely on what its inputs are right now. It does not remember anything from before — change the inputs, and the output instantly reflects the new combination.
Context Anchor
Seen in descriptions of aircraft electronic systems, avionics, and control circuits that process on/off signals.
Derivation
From 'combination' (Latin combinare, 'to join together') plus 'logic.' The name reflects what the circuit does: it produces an output by combining the current inputs according to logical rules, without reference to past states.
Why Pilots Care
Many cockpit warning and annunciator systems use combinational logic — for example, a gear-warning horn that sounds when the throttle is reduced AND the gear is up. Understanding that the output reacts only to the current input combination helps explain why such warnings appear and clear instantly with the conditions that trigger them.
Analogy
A simple room light controlled by two switches can work like combinational logic: the present positions of the switches decide whether the light is on or off. The light does not need to remember where the switches were earlier.
Intuition Check
Combinational logic does not just mean several electronic parts are combined. It means the output depends only on the present inputs, not on memory of past inputs.
Example Sentence 1
The gear warning horn uses combinational logic: it sounds whenever the throttle is at idle and the landing gear is not down and locked.
Example Sentence 2
Avionics technicians trace faults in combinational logic boards by checking that the output matches the expected result for the present input combination.