Definition
A control on the Horizontal Situation Indicator (HSI) used to rotate the course arrow to a desired magnetic course. Turning the knob positions the course pointer on the compass card, which in turn drives the course deviation bar to show the aircraft's position relative to that selected course.
Plain English
A knob on the HSI that you turn to dial in the course you want to fly. Once set, the instrument shows whether you are on that course or off to one side.
Context Anchor
Seen on an HSI in the cockpit when setting up navigation, intercepting a course, or preparing for an instrument approach.
Derivation
Course comes from a Latin word meaning a running or path. In aviation, it means the path you intend to fly. Select means choose, so the course select knob is the knob used to choose that path on the display.
Why Pilots Care
It lets the pilot set the exact course they intend to track so the HSI shows accurate deviation and heading guidance.
Intuition Check
Course here does not mean a class or lesson, and it does not just mean a vague direction. It means the specific path or direction selected on the instrument.
Example Sentence 1
Before intercepting the airway, the pilot turned the course select knob to 270 so the HSI would display deviation from that course.
Example Sentence 2
After setting the course select knob, the CDI showed the airplane left of the desired track.