Electronic Flight Instrument System

An electronic flight instrument system (EFIS) is a flight deck instrument display system that displays flight data electronically rather than electromechanically. An EFIS normally consists of a primary flight display (PFD), multi-function display (MFD), and an engine indicating and crew alerting system (EICAS) display. Early EFIS models used cathode ray tube (CRT) displays, but liquid crystal displays (LCD) are now more common. The complex electromechanical attitude director indicator (ADI) and horizontal situation indicator (HSI) were the first candidates for replacement by EFIS. Now, however, few flight deck instruments cannot be replaced by an electronic display.

EFIS installations vary greatly. A light aircraft might be equipped with one display unit that displays flight and navigation data. A large, commercial aircraft is likely to have six or more display units. Typical EFIS displays and controls can be seen at this B737 technical information web site. The equivalent electromechanical instruments are also shown here.

EFIS installation follows the sequence:

A basic EFIS might have all these facilities in the one unit.

On the flight deck, the display units are the most obvious parts of an EFIS system, and are the features that lead to the term glass cockpit. The display unit that replaces the ADI is called the primary flight display (PFD). If a separate display replaces the HSI, it is called the navigation display. The PFD displays all information critical to flight, including calibrated airspeed, altitude, heading, attitude, vertical speed and yaw. The PFD is designed to improve a pilot's situational awareness by integrating this information into a single display instead of six different analog instruments, reducing the amount of time necessary to monitor the instruments. PFDs also increase situational awareness by alerting the aircrew to unusual or potentially hazardous conditions — for example, low airspeed, high rate of descent — by changing the color or shape of the display or by providing audio alerts.

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