3.glass-cockpit-pfd. Primary Flight Display (PFD) in Glass Cockpit Aircraft
The Primary Flight Display (PFD) is the central instrument in modern glass cockpit aircraft, consolidating the traditional six-pack of analog flight instruments onto a single high-resolution color display. Rather than relying on independent gyroscopic and pressure-driven instruments, the PFD presents data derived from solid-state sensors—primarily the Air Data Computer (ADC) and the Attitude and Heading Reference System (AHRS)—and renders it in a unified, intuitive format.
Information Sources
The PFD does not generate flight data; it displays processed information from networked components:
- AHRS — Uses solid-state ring laser or MEMS gyros and accelerometers to compute pitch, roll, yaw, and magnetic heading. Replaces the spinning-mass attitude indicator, heading indicator, and turn coordinator.
- ADC — Processes pitot, static, and outside air temperature inputs to compute indicated airspeed, true airspeed, altitude, vertical speed, Mach number, and density altitude.
- Magnetometer — Provides magnetic heading reference to the AHRS, typically mounted in a wingtip or empennage to minimize magnetic interference.
- GPS/WAAS receivers and nav radios — Feed course, bearing, and deviation data.
Standard PFD Layout
Although manufacturers (Garmin G1000, Avidyne Entegra, Collins Pro Line) differ in detail, the layout is standardized to mirror the basic-T scan:
- Attitude Indicator dominates the center of the display, presenting a large, full-screen artificial horizon with pitch ladder marked in 5° or 10° increments and a sky-pointer or ground-pointer bank scale (0°, 10°, 20°, 30°, 45°, 60°).
- Airspeed tape on the left, scrolling vertically, with color-coded V-speed bands (white flap range, green normal, yellow caution, red Vne) and a trend vector indicating predicted airspeed in 6 seconds.
- Altitude tape on the right, with a selected-altitude bug, barometric setting window, and a vertical speed indicator alongside.
- Horizontal Situation Indicator (HSI) at the bottom, integrating heading, course pointer, CDI, bearing pointers, and TO/FROM flag.
- Slip/skid indicator beneath the bank pointer (replaces the inclinometer ball).
- Annunciator and alert window typically across the top, showing autopilot modes, navigation source, and system messages.
Advantages
- Single-point scan. All primary data is consolidated within a small visual area, reducing scan workload and the risk of fixation.
- Trend information. Airspeed and altitude trend vectors give the pilot a 6-second look-ahead, supporting more precise control inputs.
- Improved situational awareness. Integration with moving maps, terrain, traffic, and weather on the adjacent Multi-Function Display (MFD) provides context not available in analog cockpits.
- Reliability. Solid-state sensors have no moving parts, eliminating the precession, tumbling, and bearing wear of mechanical gyros.
- Self-test and BIT. Continuous built-in test routines monitor sensor health and flag failures with red Xs over affected fields.
Failure Modes and Indications
When a sensor fails, the PFD removes the affected indication and replaces it with a red X and an amber annunciator:
- AHRS failure — Attitude and heading display is removed. The pilot must transition to the standby attitude indicator and standby compass.
- ADC failure — Airspeed, altitude, vertical speed, and OAT-derived data are flagged. Standby airspeed and altimeter become primary.
- PFD display failure — Many systems offer a reversionary mode that consolidates PFD and MFD information onto the remaining functional screen at the press of a button.
A dedicated set of standby instruments—usually a small electric attitude indicator, airspeed indicator, and altimeter, plus a magnetic compass—remains required for IFR flight per 14 CFR §91.205. These provide independent backup if the integrated system fails.
Pilot Considerations
Transitioning from analog to glass demands new habits:
- Tape interpretation. Numeric tapes do not give the at-a-glance "position of the needle" cue of round dials. Pilots must learn to read trend, magnitude, and rate from scrolling numbers.
- Bug management. Selected altitude, heading, airspeed, and course bugs become the primary tactical tools; setting them correctly is part of every clearance and altitude change.
- Knob and softkey fluency. A glass cockpit pilot must know how to change the altimeter setting, swap nav sources, load approaches, and reconfigure displays without heads-down fixation.
- System knowledge. Pilots are expected to understand which sensors feed which displays, how to recognize a partial failure, and how to enter reversionary mode.
The PFD does not change the fundamentals of instrument flight; the basic-T scan, attitude-instrument flying, and cross-check techniques still apply. What changes is the medium: a software-rendered presentation that demands competence in both flying and managing the avionics suite.