Primary flight display
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A Chelton primary flight display (left) and navigation display in the cockpit of a Piper Seneca. |
A
primary flight display, commonly referred to as
PFD, is a modern
aircraft instrument dedicated to flight information. Much like
multi-function displays, the PFD consists of either 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.
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. Thus, the digitally enhanced LCD or CRT display is purely visual.
Even though several modern aircraft contain PFDs, the pilot still has access to all of the various mechanical gauges represented by the primary display. This is so that, in the event of an electrical failure, the mechanical systems would still function reliably.
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A common layout of a Primary Flight Display |
PFDs vary slightly in appearance and arrangement of information, but they are more or less indentical in how they present information to the pilot.
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 second." For example, a measurement of "+2" indicates an ascent of 2000 feet per second, while a measurement of "-1.5" indicates a descent of 1500 feet per second.
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.
Most
airliners built since the
1980s â€" as well as many
business jets and an increasing number of newer
general aviation aircraft â€" are equipped with primary flight and multi-function displays.
As discussed, standard mechanical gauges have not been completely eliminated from the cockpit with the onset of the PFD. The primary display is simply used to allow the pilot to scan all of the major flight instruments and gauges at a glance. Because of the display's reliance on the electrical power of the aircraft, it is not as wholly reliable as non-electrical barometric gauges.
