Heading Indicator

The heading indicator, sometimes called the "directional gyro" or "DG," is one of the three gyro instruments. When aligned with the compass, it provides an accurate, stable indication of the aircraft's magnetic heading.

The heading indicator is an important aid because the compass is subject to errors caused by acceleration, deceleration, and the curvature of the earth's magnetic field, especially at high latitudes. The compass often oscillates or leads or lags a turn and it is especially hard to read in turbulence or during maneuvers. (To see how difficult it is to fly with only a compass, you can display a compass in a separate window. On the Views menu, click Instrument Panel and then click Compass.)

How It Works

The gyro in the heading indicator rotates in the vertical plane. A card marked with headings maintains its orientation as the airplane turns. The apparent movement of the card gives the pilot an immediate, precise indication of the airplane's heading and the direction in which the airplane is turning.

The card is marked off in five-degree increments, with numbers every 30 degrees and the cardinal directions indicated by N, S, E, W.

Aligning the Heading Indicator

On small aircraft like the Cessna 182RG, the pilot sets the heading indicator to coincide with the compass before takeoff and resets it periodically during flight to make sure that it remains in sync with the compass. The heading indicator drifts because it's based on a gyro, which precesses with time. As a rule, the heading should drift no more than three degrees every 15 minutes.Larger aircraft usually have "slaved" heading indicators that automatically keep the instrument properly aligned with the compass.

NOTE: You can make the heading indicator drift in Flight Simulator by selecting the Gyro Drift option on the Instrument tab of the Preferences dialog box.