What does the heading indicator show?
A round compass card turns behind a fixed airplane symbol. The number at the top, under the airplane’s nose, is the heading. The card turns the opposite way to the aircraft, so a turn to the right brings bigger numbers to the top.
Why not just use the magnetic compass? A magnetic compass swings and gives wrong readings in turns, when speeding up or slowing down, and in rough air. The heading indicator stays steady, so it is much easier to fly by.
How do you read the markings?
| Marking | What it means |
|---|---|
| Airplane symbol and top index | Fixed. The card under the nose is the heading. |
| Fixed marks around the edge | Every 45° from the nose. They show at a glance the heading 45°, 90° or 180° away, for example for a 90° turn. |
| N, E, S, W | North (360), east (090), south (180) and west (270). |
| 3, 6, 12, 15, 21, 24, 30, 33 | Headings with the last zero left off: 3 is 030, 33 is 330. |
| Marks | A mark every 5°, a longer one every 10°, and a long one with a number or letter every 30°. |
| PUSH knob (lower left) | Sets the card. On a real instrument you push it in and turn it, to match the compass. |
| HDG knob and bug (lower right) | The orange bug on the card marks a heading you want to remember or fly. Many autopilots follow it. |
How do you set it from the compass?
- Fly straight and level at a steady speed, so the magnetic compass settles.
- Read the heading on the magnetic compass.
- Push in the knob and turn it until the heading indicator shows the same heading.
- Check it again from time to time during the flight, and reset it when it has drifted.
How does it work inside?
Inside is a gyroscope spinning with its axis level. Thanks to its rigidity in space, it keeps pointing the same way while the aircraft turns around it, and gears turn the card to match. In most light aircraft the gyro is spun by the vacuum system, like the attitude indicator.
The gyro does not know where north is. It only keeps the direction it was given, which is why it has to be set from the magnetic compass.
What can go wrong?
- Drift (precession). Friction in the gyro slowly makes the card creep away from the right heading. Compare it with the compass regularly and reset it.
- Setting it during a turn. The compass is only reliable in straight, level, steady flight. Set the heading indicator then, not while turning or changing speed.
- Vacuum failure. Like the attitude indicator, it stops working properly if the vacuum system fails. Fall back on the magnetic compass.
Questions
Is the heading indicator the same as a directional gyro?
Yes. "Directional gyro" (DG) is another name for it.
Why does the heading indicator drift?
Friction inside the gyro makes it precess: the card slowly creeps away from the true heading. That is why pilots check it against the magnetic compass during the flight.
How do I reset the heading indicator?
In straight and level flight at a steady speed, read the magnetic compass, then push and turn the knob until the heading indicator matches.
What is the orange bug for?
It marks a chosen heading. You set it with the HDG knob; many autopilots use it to know which way to fly.
Does the SkyDeck heading indicator drift?
Not in the app: it shows the heading your simulator sends. The drift on this page is there to show what happens in a real aircraft.
Source
- Federal Aviation Administration, Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 8, Flight Instruments.