Definition
A flight director and autopilot mode that commands the aircraft to turn to and maintain a magnetic heading selected by the pilot using the heading bug on the heading indicator or HSI. When engaged, the flight director computes the bank required to capture the bug, and the autopilot (if coupled) flies the aircraft to that heading and holds it.
Plain English
A mode you switch on so the autopilot will turn the aircraft to whatever direction you set with the heading bug, and then keep it pointed that way.
Context Anchor
Seen when using a flight director or autopilot, especially on the mode display after selecting a heading to fly.
Derivation
HDG is a common cockpit abbreviation for heading, meaning the direction the airplane’s nose is pointed. Mode means the selected way a system is operating. Together, HDG mode means the system is operating by reference to a selected heading.
Why Pilots Care
It lowers workload by letting the system handle turns and heading hold instead of the pilot constantly adjusting the controls.
Intuition Check
Do not assume HDG mode follows a charted route or a course line. It follows the heading you selected, which is simply the direction the airplane is pointed.
Example Sentence 1
After takeoff, the pilot set the heading bug to 270 and engaged HDG mode to fly the assigned vector.
Example Sentence 2
After takeoff, HDG mode kept the aircraft on the departure heading until the next vector was received.