Electronic Flight Instrument | EADI and EHSI Explained

EHSI & EADI image download

Electronic Flight Instruments

Modern aircraft are extensively using electronic instruments and display these days. One advantage of electronic instruments is that the aircraft system data can easily be exchanged between different instrument systems and used as a main source for automatic flight control.  The two most important electronic instruments in the EFIS (Electronic Flight Instrument Systems) are the EADI (Electronic Attitude and Direction Indicator) and the EHSI (Electronic Horizontal Situation Indicator).

Electronic Attitude and Direction Indicator (EADI)

Electronic Attitude and Direction Indicator (EADI) image download

The (EADI) Electronic Attitude Direction Indicator is designed to replace the basic ADI and normally includes the following:

• Attitude indicator

• Fixed aircraft symbol

• Pitch and bank command bars

• Glide slope indicator

• Localizer deviation indicator

• Slip indicator

• Flight mode annunciator

• Various warning flags.

The fixed aircraft symbol and the flight command bars show the aircraft's position in relation to the horizon. The pilot can select one of three flight modes by adjusting the symbol. The pilot just inserts the aircraft icon between the command bars to fly the plane with the command bars armed.

The command bars move up or down for climbing or descending, and they roll left or right for lateral guidance. They show the calculated bank angle for standard-rate turns, allowing the pilot to reach and fly a desired heading or track.

Pitch commands are also displayed in the bars, allowing the pilot to capture and fly an ILS glide slope, a pre-set pitch attitude, or maintain a selected barometric altitude. The pilot maneuvers the aircraft to align the fixed symbol with the command bars in order to follow the directions indicated by the command bars. When the pilot isn't using the bars, he or she can slide them out of sight.

The glide slope deviation pointer shows the vertical deviation of the aircraft from the glide slope center and indicates the center of the instrument landing system (ILS) glide slope. The glide slope scale's centerline depicts the position of the aircraft in relation to the glide slope.

When the pilot has acquired the glide slope, the localizer deviation pointer, which is a symbolic runway, appears. It symbolizes the center of the ILS localizer. The extended scale movement depicts lateral departure from the localizer and is roughly twice as sensitive as the horizontal situation indicator's lateral deviation bar. For pitch modes, the selected flying mode is indicated in the lower left of the EADI, while for lateral modes, it is displayed in the lower right. Slip or skid indications are indicated by the slip indicator.

Electronic Horizontal Situation Indicator (EHSI)

Electronic Horizontal Situation Indicator (EHSI) image donload

The electronic horizontal situation indicator (EHSI) aids pilots in the interpretation of data provided by a variety of navigational aids. EHSIs come in a variety of shapes and sizes, but they all serve the same purpose. An EHSI display can be set up to show a wide range of data (combined in a variety of ways), including:

Heading indication

Radio Magnetic indication (RMI)

Track indication

Range indication

Wind speed and direction

VOR, DME, ILS or ADF information.

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