An integral component of modern aviation is the series of flight instruments that work together to provide the crew with valuable information about the aircraft. In the cockpit, you may notice dozens of gauges and meters, some of which are used frequently, and others rarely. Of these many instruments, one of the most commonly used throughout the flight is the attitude indicator or artificial horizon. This critical component provides real-time information to the pilot about the aircraft's orientation. In this blog, we will discuss everything you need to know about the artificial horizon instrument, including its design and implementation.
The face of the artificial horizon instrument includes a blue upper-half, a brown lower-half, and a dipole representation of the aircraft's wings. These elements represent the sky, ground, and aircraft, respectively. In addition, there are several reference lines throughout the top of the instrument and near the reference aircraft. The uppermost group of vertical lines indicates the angle of a bank in degrees from 10-60°, while the centered horizontal lines denote pitch.
Artificial horizons make use of an electric-powered gyroscope that is mounted on a 4-axis gimbal. While most gyroscopes are powered directly from an electric motor, many aircraft in operation employ an air-powered system. As the plane experiences a change in magnitude in either pitch or roll, the gyro will resist the positional change and move upright. This gyroscopic motion is then sensed by a series of small pendulums that, when swinging, cause a change on the instrument face.
During visual flight rule (VFR) conditions, the pilot is generally able to surmise most of the information they need about pitch and roll by looking outside the window of the cockpit, making the artificial horizon inutile in such conditions. However, when operating under instrument flight rules (IFR), the attitude indicator is checked frequently to help the flight crew orient themselves to the horizon. With incredible sensitivity, a properly functioning artificial horizon provides quick feedback on the slightest changes in pitch or roll.
While artificial horizons are used daily in flight operations across the globe without issue, there are some limitations and occasional errors produced by the instrument. For example, as the aircraft accelerates and decelerates, there is a tendency for the pitch to erroneously move due to acceleration's association with gravity. While the error is usually minute, it may last for up to 5 minutes when it occurs. Additionally, for aerobatic aircraft performing deep rolls, there may be a lingering pitch error when returning to level flight.
Before each flight, the pilot should ensure that the artificial horizon is upright and neutral. While it may appear to be banking slightly during taxiing, the roll pointer should not deviate by more than 5° in either direction before takeoff. Another sign that the instrument may need maintenance is precession, which occurs when the electric motor or air-vane system operates incorrectly or when the associated bearing component becomes worn out.
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