Primary flight display
From Wikipedia, the free encyclopedia
A primary flight display or PFD is a modern aircraft instrument dedicated to flight information. Much like multi-function displays, primary flight displays are built around an LCD or CRT display device. Representations of older "steam gauge" instruments are combined on one compact display, simplifying pilot workflow and streamlining cockpit layouts.
Most airliners built since the 1980s — as well as many business jets and an increasing number of newer general aviation aircraft — have glass cockpits equipped with primary flight and multi-function displays.
Mechanical gauges have not been completely eliminated from the cockpit with the onset of the PFD; they are retained for backup purposes in the event of total electrical failure.
[edit] Components
While the PFD does not directly use the pitot-static system to physically display flight data, it still uses the system to make altitude, airspeed, vertical speed, and other measurements precisely using air pressure and barometric readings. An air data computer analyzes the information and displays it to the pilot in a readable format. A number of manufacturers produce PFDs, varying slightly in appearance and functionality, but the information is displayed to the pilot in a similar fashion.
[edit] Layout
The center of the PFD usually contains an attitude indicator, which gives the pilot information about the aircraft's pitch and roll characteristics, and the orientation of the aircraft with respect to the horizon. Unlike a traditional attitude indicator, however, the mechanical gyroscope is not contained within the panel itself, but is rather a separate device whose information is simply displayed on the PFD.
To the left and right of the attitude indicator are the airspeed and altitude indicators, respectively. The airspeed indicator displays the speed of the aircraft in knots, while the altitude indicator displays the aircraft's altitude above sea level (MSL). These measurements are conducted through the aircraft's pitot system, which tracks air pressure measurements. As in the PFD's attitude indicator, these systems are merely displayed data from the underlying mechanical systems, and do not contain any mechanical parts (unlike an aircraft's airspeed indicator and altimeter).
The vertical speed indicator, usually next to the altitude indicator, indicates to the pilot how fast the aircraft is ascending or descending, or the rate at which the altitude changes. This is usually represented with numbers in "thousands of feet per minute." For example, a measurement of "+2" indicates an ascent of 2000 feet per minute, while a measurement of "-1.5" indicates a descent of 1500 feet per minute.
At the bottom of the PFD is the heading display, which shows the pilot the magnetic heading of the aircraft. This functions much like a standard magnetic heading indicator.
Other information displayed on the PFD includes navigational marker information, bugs (to control the autopilot), ILS glideslope indicators, course deviation indicators, altitude indicator QFE settings, and much more.
