What does the attitude indicator show?
It is a picture of the aircraft against the horizon. The miniature airplane in the middle is fixed to the case and stands for your aircraft. Behind it, the horizon card moves: sky above, ground below, with a line where they meet.
When the miniature airplane sits above the horizon line, the nose is up. When the horizon tilts, the aircraft is banked. It is the one instrument that shows both pitch and bank at a glance, which is why it is used so much when flying by instruments.
How do you read the markings?
| Marking | What it is | How to read it |
|---|---|---|
| Miniature airplane | Two wing bars and a centre dot, fixed to the case | Your aircraft. Compare it with the horizon line. |
| Horizon line | Where the sky meets the ground on the moving card | Airplane above it: nose up. Below it: nose down. |
| Pitch lines | Short lines every 5° up to 20°, above and below; the long ones are labelled 10 and 20 | The line the airplane’s dot sits on is the pitch angle. |
| Bank scale | Marks at 10, 20, 30, 60 and 90° on the ring around the top, either side | The ring turns with the horizon. The mark under the orange triangle at the top is the bank angle. |
| Orange triangle | The fixed index at the top | Points to zero bank when the wings are level. |
| Knob | At the bottom of the dial | On a real instrument it moves the miniature airplane up or down to line it up with the horizon in level flight. On SkyDeck it is drawn only. |
| VACUUM | Printed on the lower cover | This gyro is driven by the vacuum system. |
In a steady 30° bank, the 30 mark sits under the triangle. Try it with the button under the instrument.
How does it work inside?
Inside is a gyroscope: a heavy wheel spinning very fast. A spinning gyro has rigidity in space: it keeps pointing the same way however the case around it moves. The horizon card is tied to the gyro, so it stays level with the real horizon while the aircraft pitches and rolls around it.
In most light aircraft the gyro is spun by air. A vacuum pump on the engine pulls air through the instrument, and the air turns the wheel. A suction gauge on the panel shows whether the vacuum system is working. Some aircraft use electric gyros instead.
What can go wrong?
- Vacuum failure. If the vacuum pump stops, the gyro slowly runs down and the horizon starts to lean or drift, often so slowly that it is hard to notice. Check the suction gauge, and cross-check with the turn coordinator, heading indicator and altimeter. That is how a failing gyro is caught early.
- Acceleration and deceleration. A quick speed-up can show a small nose-up error, and a quick slow-down a small nose-down error.
- Only looking at this one instrument. Pilots scan all the instruments and use each to confirm the others.
Questions
Is the attitude indicator the same as an artificial horizon?
Yes. Both names are used for the same instrument.
What makes the attitude indicator work?
A gyroscope. In most light aircraft it is spun by air drawn through the instrument by a vacuum pump.
What happens if the vacuum pump fails?
The gyro slows down and the indicator becomes wrong, slowly. Watch the suction gauge and cross-check with the other instruments.
How do I read bank on the attitude indicator?
Look at the orange triangle at the top. The mark on the turning ring under it is the bank angle: 10, 20, 30, 60 or 90 degrees.
Does SkyDeck’s attitude indicator move with my simulator?
Yes. Connected to X-Plane 12, SkyDeck shows the pitch and bank the simulator sends, live. Microsoft Flight Simulator support is in testing.
Source
- Federal Aviation Administration, Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 8, Flight Instruments.