Heading Indicator

The heading indicator (HI), also called the directional gyro (DG), is a gyroscopic flight instrument that displays aircraft heading. Unlike the magnetic compass, the heading indicator is not subject to turning errors, acceleration errors, or oscillation — it gives a stable, smooth heading reference that is essential for instrument flight.

How It Works

The heading indicator uses a gyroscope maintained in a horizontal plane. The aircraft rotates around the gyro, and the heading card (calibrated 0–360°) shows the aircraft’s current heading. The HI must be aligned with the magnetic compass periodically (typically every 15 minutes) because gyroscopic precession causes gradual drift.

Setting the Heading Indicator

Set the HI to the magnetic compass reading after the compass has settled (straight and level, no turns or acceleration). Re-check alignment every 15 minutes in cruise and immediately before any instrument approach. In bumpy conditions, the compass may be unreadable — set the HI during a brief period of smooth air.

AHRS Replacement

Modern glass cockpit aircraft use an Attitude and Heading Reference System (AHRS) which combines solid-state gyros and accelerometers. AHRS units do not precess and require no periodic resetting — they maintain accurate heading continuously. They do, however, still use magnetic flux gate sensors to reference to magnetic north.

Related Terms

See also: Attitude Indicator, Turn and Slip Indicator, Heading.