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)
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)
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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