Primary flight display
Encyclopedia
A primary flight display or PFD is a modern aircraft instrument
dedicated to flight information. Much like multi-function display
s, primary flight displays are built around an LCD or CRT
display device
. Representations of older six pack
or "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 cockpit
s 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.
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.
The center of the PFD usually contains an attitude indicator
(AI), 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. The attitude indicator is designed to look very much like traditional mechanical AI's. Other information that may or may not appear on or about the attitude indicator can include the stall
angle, a runway diagram, ILS
localizer and glide-path “needles”, and so on. Unlike mechanical instruments, this information can be dynamically updated as required; the stall angle, for example, can be adjusted in real time to reflect the calculated critical angle of attack
of the aircraft in its current configuration (airspeed, etc.). The PFD may also show an indicator of the aircraft's future path (over the next few seconds), as calculated by onboard computers, making it easier for pilots to anticipate aircraft movements and reactions.
To the left and right of the attitude indicator are usually 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 mean sea level (AMSL). 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
). Both of these indicators are usually presented as vertical “tapes”, which scroll up and down as altitude and airspeed change. Both indicators may often have “bugs”, that is, indicators that show various important speeds and altitudes, such as V speeds
calculated by a flight management system
, do-not-exceed speeds for the current configuration, stall speeds, selected altitudes and airspeeds for the autopilot, and so on.
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. There may also be a simulated needle showing the general direction and magnitude of vertical movement.
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
, turning as required. Often this part of the display shows not only the current heading, but also the current track (actual path over the ground), current heading setting on the autopilot, and other indicators.
Other information displayed on the PFD includes navigational marker information, bugs (to control the autopilot
), ILS
glideslope indicators, course deviation indicator
s, altitude indicator QFE
settings, and much more.
Although the layout of a PFD can be very complex, once a pilot is accustomed to it the PFD can provide an enormous amount of information with a single glance.
A failure of a PFD deprives the pilot of an extremely important source of information. While backup instruments will still provide the most essential information, they may be spread over several locations in the cockpit, which must be scanned by the pilot, whereas the PFD presents all this information on one display. Additionally, some of the less important information, such as speed and altitude bugs, stall angles, and the like, will simply disappear if the PFD malfunctions; this may not endanger the flight, but it does increase pilot workload and diminish situational awareness.
Flight instruments
Flight instruments are the instruments in the cockpit of an aircraft that provide the pilot with information about the flight situation of that aircraft, such as height, speed and altitude...
dedicated to flight information. Much like multi-function display
Multi-function display
A Multi-function display is a small screen in an aircraft surrounded by multiple buttons that can be used to display information to the pilot in numerous configurable ways. Often an MFD will be used in concert with a Primary Flight Display. MFDs are part of the digital era of modern planes or...
s, primary flight displays are built around an LCD or CRT
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
display device
Display device
A display device is an output device for presentation of information in visual or tactile form...
. Representations of older six pack
Flight instruments
Flight instruments are the instruments in the cockpit of an aircraft that provide the pilot with information about the flight situation of that aircraft, such as height, speed and altitude...
or "steam gauge" instruments are combined on one compact display, simplifying pilot
Aviator
An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...
workflow and streamlining cockpit
Cockpit
A cockpit or flight deck is the area, usually near the front of an aircraft, from which a pilot controls the aircraft. Most modern cockpits are enclosed, except on some small aircraft, and cockpits on large airliners are also physically separated from the cabin...
layouts.
Most airliners built since the 1980s — as well as many business jets and an increasing number of newer general aviation
General aviation
General aviation is one of the two categories of civil aviation. It refers to all flights other than military and scheduled airline and regular cargo flights, both private and commercial. General aviation flights range from gliders and powered parachutes to large, non-scheduled cargo jet flights...
aircraft — have glass cockpit
Glass cockpit
A glass cockpit is an aircraft cockpit that features electronic instrument displays, typically large LCD screens, as opposed to the traditional style of analog dials and gauges...
s 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.
Components
While the PFD does not directly use the pitot-static systemPitot-static system
A pitot-static system is a system of pressure-sensitive instruments that is most often used in aviation to determine an aircraft's airspeed, Mach number, altitude, and altitude trend. A pitot-static system generally consists of a pitot tube, a static port, and the pitot-static instruments...
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
Barometer
A barometer is a scientific instrument used in meteorology to measure atmospheric pressure. Pressure tendency can forecast short term changes in the weather...
readings. An air data computer
Air data computer
An air data computer is an essential avionics component found in modern glass cockpits. This computer, rather than individual instruments, can determine the calibrated airspeed, Mach number, altitude, and altitude trend from input data from sensors such as an aircraft's pitot-static system,...
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.
Layout
The details of the display layout on a primary flight display can vary enormously, depending on the aircraft, the aircraft's manufacturer, the specific model of PFD, certain settings chosen by the pilot, and various internal options that are selected by the aircraft's owner (i.e., an airline, in the case of a large airliner). However, the great majority of PFDs follow a similar layout convention.The center of the PFD usually contains an attitude indicator
Attitude indicator
An attitude indicator , also known as gyro horizon or artificial horizon, is an instrument used in an aircraft to inform the pilot of the orientation of the aircraft relative to earth. It indicates pitch and bank or roll and is a primary instrument for flight in instrument meteorological conditions...
(AI), which gives the pilot information about the aircraft's pitch and roll
Flight dynamics
Flight dynamics is the science of air vehicle orientation and control in three dimensions. The three critical flight dynamics parameters are the angles of rotation in three dimensions about the vehicle's center of mass, known as pitch, roll and yaw .Aerospace engineers develop control systems for...
characteristics, and the orientation of the aircraft with respect to the horizon
Horizon
The horizon is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting...
. Unlike a traditional attitude indicator, however, the mechanical gyroscope
Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...
is not contained within the panel itself, but is rather a separate device whose information is simply displayed on the PFD. The attitude indicator is designed to look very much like traditional mechanical AI's. Other information that may or may not appear on or about the attitude indicator can include the stall
Stall (flight)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...
angle, a runway diagram, ILS
Instrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
localizer and glide-path “needles”, and so on. Unlike mechanical instruments, this information can be dynamically updated as required; the stall angle, for example, can be adjusted in real time to reflect the calculated critical angle of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
of the aircraft in its current configuration (airspeed, etc.). The PFD may also show an indicator of the aircraft's future path (over the next few seconds), as calculated by onboard computers, making it easier for pilots to anticipate aircraft movements and reactions.
To the left and right of the attitude indicator are usually the airspeed
Airspeed
Airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are: indicated airspeed , calibrated airspeed , true airspeed , equivalent airspeed and density airspeed....
and altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
indicators, respectively. The airspeed indicator displays the speed of the aircraft in knots, while the altitude indicator displays the aircraft's altitude above mean sea level (AMSL). These measurements are conducted through the aircraft's pitot
Pitot-static system
A pitot-static system is a system of pressure-sensitive instruments that is most often used in aviation to determine an aircraft's airspeed, Mach number, altitude, and altitude trend. A pitot-static system generally consists of a pitot tube, a static port, and the pitot-static instruments...
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
Airspeed indicator
The airspeed indicator or airspeed gauge is an instrument used in an aircraft to display the craft's airspeed, typically in knots, to the pilot.- Use :...
and altimeter
Altimeter
An altimeter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth underwater.-Pressure altimeter:...
). Both of these indicators are usually presented as vertical “tapes”, which scroll up and down as altitude and airspeed change. Both indicators may often have “bugs”, that is, indicators that show various important speeds and altitudes, such as V speeds
V speeds
In aviation, V-speeds are standard terms used to define airspeeds important or useful to the operation of all aircraft including fixed-wing aircraft, gliders, autogiros, helicopters, and dirigibles...
calculated by a flight management system
Flight management system
A flight management system is a fundamental part of a modern airliner's avionics. An FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that modern aircraft no longer carry flight engineers or navigators. A...
, do-not-exceed speeds for the current configuration, stall speeds, selected altitudes and airspeeds for the autopilot, and so on.
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. There may also be a simulated needle showing the general direction and magnitude of vertical movement.
At the bottom of the PFD is the heading
Bearing (navigation)
In marine navigation, a bearing is the direction one object is from another object, usually, the direction of an object from one's own vessel. In aircraft navigation, a bearing is the actual compass direction of the forward course of the aircraft...
display, which shows the pilot the magnetic heading of the aircraft. This functions much like a standard magnetic heading indicator
Heading indicator
The heading indicator is a flight instrument used in an aircraft to inform the pilot of the aircraft's heading. It is sometimes referred to by its older names, the directional gyro or DG, and also direction indicator or DI.- Use :The primary means of establishing the heading in most small...
, turning as required. Often this part of the display shows not only the current heading, but also the current track (actual path over the ground), current heading setting on the autopilot, and other indicators.
Other information displayed on the PFD includes navigational marker information, bugs (to control the autopilot
Autopilot
An autopilot is a mechanical, electrical, or hydraulic system used to guide a vehicle without assistance from a human being. An autopilot can refer specifically to aircraft, self-steering gear for boats, or auto guidance of space craft and missiles...
), ILS
Instrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
glideslope indicators, course deviation indicator
Course deviation indicator
Course Deviation Indicator is an avionics instrument used in aircraft navigation to determine an aircraft's lateral position in relation to a track. If the location of the aircraft is to the left of course, the needle deflects to the right, and vice versa.-Use:The instrument shows the direction...
s, altitude indicator QFE
QFE
QFE is a three letter acronym which can have meanings in aviation, in software development, and in network usage. It can refer to*QFE, a Q code used by pilots and air traffic control that refers to atmospheric pressure and altimeter settings...
settings, and much more.
Although the layout of a PFD can be very complex, once a pilot is accustomed to it the PFD can provide an enormous amount of information with a single glance.
Drawbacks
The great variability in the precise details of PFD layout makes it necessary for pilots to study the specific PFD of the specific aircraft they will be flying in advance, so that they know exactly how certain data are presented. While the basics of flight parameters tend to be much the same in all PFDs (speed, attitude, altitude), much of the other useful information presented on the display is shown in different formats on different PFDs. For example, one PFD may show the current angle of attack as a tiny dial near the attitude indicator, while another may actually superimpose this information on the attitude indicator itself. Since the various graphic features of the PFD are not labeled, the pilot must learn what they all mean in advance.A failure of a PFD deprives the pilot of an extremely important source of information. While backup instruments will still provide the most essential information, they may be spread over several locations in the cockpit, which must be scanned by the pilot, whereas the PFD presents all this information on one display. Additionally, some of the less important information, such as speed and altitude bugs, stall angles, and the like, will simply disappear if the PFD malfunctions; this may not endanger the flight, but it does increase pilot workload and diminish situational awareness.