# Attitude Indicator (Artificial Horizon): Erection Systems and Errors

> Study artificial-horizon operation, including vertical gyro erection systems, acceleration/turning errors, and ADI integration for instrument flight.

- **Subject:** 022 — Instrumentation
- **Section:** 022-04 — Gyroscopic Instruments
- **Topic code:** 022-04-03
- **Last reviewed:** 2026-03-27
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/instrumentation/gyroscopic-instruments/attitude-indicator-artificial-horizon/

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The **Attitude Indicator (AI)** or Artificial Horizon provides pitch and roll information relative to the Earth's horizon. It is the only instrument that gives an immediate, direct picture of the aircraft's attitude.

## Principles
*   **Gyro:** **Earth Gyro** (Spin axis is vertical).
*   **Degrees of Freedom:** **2** (Pitch and Roll).
*   **Erection System:** The gyro must remain vertical relative to the Earth.
    *   **Air-Driven:** Uses **Pendulous Vanes**. Gravity acts on the vanes to open/close air ports, creating a precession force to right the gyro.
    *   **Electrically-Driven:** Uses torque motors and mercury/bubble switches.

## Indication Errors (Air-Driven)
Air-driven AIs suffer from specific errors caused by the movement of the pendulous vanes during maneuvers.
1.  **Acceleration Error:**
    *   During acceleration, the vanes lag, causing a false precession.
    *   Indication: **False Climb (Pitch Up) + False Turn to the Right**.
    *   *Correction during Deceleration:* False Descent + Turn Left.
2.  **Turning Error:**
    *   During a turn, centrifugal force acts on the vanes.
    *   Errors in both pitch and bank indications, but usually small in modern instruments.

## The Attitude Director Indicator (ADI)
An advanced version of the AI found in modern cockpits.
*   Inputs: Pitch/Roll Gyro + Flight Computer.
*   Displays: **Flight Director (Command Bars)**, ILS deviations (Localizer/Glideslope), and sometimes Speed/Altitude tapes (EFIS).
*   **Color:** Blue (Sky) / Brown (Ground).

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Free study notes from pilotsyllabus.com. Not a substitute for training at an approved ATO.