Definition
A control system in which the output is continuously measured and compared against a desired value, and any difference between the two is automatically used to adjust the input so the output stays at the desired value.
Plain English
A system that watches its own results and corrects itself. It checks what it's actually doing, compares it to what it's supposed to be doing, and adjusts on its own to fix any difference.
Context Anchor
Seen in aircraft systems that automatically control or stabilize something, such as an autopilot holding altitude or a system maintaining a selected engine or flight condition.
Derivation
Closed-loop describes the shape of the signal path: the output is fed back to the input, closing the loop. Feedback means information about the result is sent back to the controller. Together they describe a system that listens to itself and corrects.
Why Pilots Care
It allows automatic systems to maintain precise flight parameters with minimal pilot input, improving accuracy and reducing workload.
Analogy
A home thermostat. It measures the actual room temperature, compares it to the temperature you set, and turns the heater on or off to close the gap. The heater's effect (warmer room) is fed back to the thermostat, which keeps adjusting.
Grounding Statement
The key idea is simple: the system does not just act once; it checks the result and adjusts.
Intuition Check
Closed does not mean shut off or unavailable here. It means the feedback path is complete, so the system can use the result of its own action to make corrections.
Example Sentence 1
The autopilot uses a closed-loop feedback system to hold altitude, constantly comparing the aircraft's actual altitude to the selected altitude and adjusting pitch to correct any difference.
Example Sentence 2
During turbulence, the stability augmentation system uses closed-loop feedback to sense roll rate and apply opposite aileron input.