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Electronic flight instrument system

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Electronic flight instrument system

In aviation, an electronic flight instrument system (EFIS) is a flight instrument display system in an aircraft cockpit 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.

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 artificial horizon 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.

The names Electronic Attitude Director Indicator and Electronic Horizontal Situation Indicator are used by some manufacturers. However, a simulated ADI is only the centerpiece of the PFD. Additional information is both superimposed on and arranged around this graphic.

Multi-function displays can render a separate navigation display unnecessary. Another option is to use one large screen to show both the PFD and navigation display.

The PFD and navigation display (and multi-function display, where fitted) are often physically identical. The information displayed is determined by the system interfaces where the display units are fitted. Thus, spares holding is simplified: the one display unit can be fitted in any position.

LCD units generate less heat than CRTs; an advantage in a congested instrument panel. They are also lighter, and occupy a lower volume.

The MFD (multi-function display) displays navigational and weather information from multiple systems. MFDs are most frequently designed as "chart-centric", where the aircrew can overlay different information over a map or chart. Examples of MFD overlay information include the aircraft's current route plan, weather information from either on-board radar or lightning detection sensors or ground-based sensors, e.g., NEXRAD, restricted airspace and aircraft traffic. The MFD can also be used to view other non-overlay type of data (e.g., current route plan) and calculated overlay-type data, e.g., the glide radius of the aircraft, given current location over terrain, winds, and aircraft speed and altitude.

MFDs can also display information about aircraft systems, such as fuel and electrical systems (see EICAS, below). As with the PFD, the MFD can change the color or shape of the data to alert the aircrew to hazardous situations.

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