7.glass-cockpit-pfd-mfd. Glass Cockpit: Primary Flight Display (PFD) and Multi-Function Display (MFD)
The term glass cockpit refers to a flight deck in which traditional electromechanical ("steam gauge") instruments have been replaced by one or more large electronic displays that integrate flight, navigation, engine, and systems information. In a typical light-airplane installation (e.g., Garmin G1000, Avidyne Entegra), two color LCD screens dominate the panel: the Primary Flight Display (PFD) in front of the pilot and the Multi-Function Display (MFD) to the right. Together they consolidate the data formerly provided by the six-pack, navigation radios, transponder, autopilot mode annunciator, engine cluster, and chart plotter into a unified, software-driven presentation.
Primary Flight Display (PFD)
The PFD presents the six core flight parameters in a layout patterned after a head-up display:
- Attitude indicator — a large central artificial horizon with pitch ladder and bank pointer, often spanning the full width of the screen.
- Airspeed tape — vertical scrolling tape on the left, with color-coded arcs (white flap range, green normal, yellow caution, red Vne) and trend vector showing predicted airspeed in 6 seconds.
- Altimeter tape — vertical scrolling tape on the right with selected-altitude bug and altitude alerter.
- Vertical speed indicator (VSI) — adjacent to the altitude tape, often with a digital readout.
- Heading/HSI — a slaved magnetic compass rose at the bottom showing track, course, bearing pointers, and CDI/glideslope deviation.
- Slip/skid indicator — a small trapezoid beneath the bank pointer that replaces the inclinometer ball.
Surrounding these primary tapes are softkey-driven windows for navigation source, transponder, com/nav frequencies, OAT, wind vector, and autopilot/flight director modes. The PFD is driven by the Air Data Computer (ADC) — which processes pitot, static, and OAT inputs — and the Attitude and Heading Reference System (AHRS) — which uses solid-state ring-laser or MEMS gyros and accelerometers, plus a magnetometer, to compute attitude and heading. Because the AHRS is solid-state, there is no spin-up time delay like a vacuum gyro, but it does require a brief ground initialization and must not be moved during alignment.
Multi-Function Display (MFD)
The MFD typically presents:
- A moving map with terrain, airspace, airports, NAVAIDs, victor airways, weather overlays (NEXRAD, METARs, TFRs via ADS-B In or SiriusXM), and traffic (TIS-B/TAS/TCAS).
- An engine indication strip along the left edge showing RPM, manifold pressure, fuel flow, fuel quantity, oil temp/pressure, electrical bus voltages, and EGT/CHT bars.
- Pages for flight planning, direct-to, procedures (DPs, STARs, approaches), nearest airport/NAVAID, checklists, and system status.
The MFD can also display a reversionary (composite) PFD if the primary screen fails — typically activated automatically or via a red REVERSION button. In reversionary mode, one screen shows the full PFD plus the engine strip.
Architecture and Redundancy
All data flow through Line Replaceable Units (LRUs) connected by a digital data bus. A typical system includes dual ADCs, dual AHRS, dual GPS/NAV/COM units, a magnetometer, an integrated avionics processor, and an audio panel. Redundancy is built around:
- Backup (standby) instruments — at minimum an independent attitude indicator (often electric with its own battery), altimeter, and airspeed indicator, required because total electrical failure would otherwise leave the pilot without primary references.
- Independent power sources — essential bus, standby battery, and in some installations a dedicated standby alternator.
- Cross-checking — the system continuously compares dual ADC/AHRS outputs and annunciates a MISCOMPARE or ATTITUDE FAIL when values diverge.
Operational Considerations
Glass cockpits dramatically improve situational awareness, but they introduce new pilot workload patterns:
- Automation management. The pilot must understand what mode the autopilot/flight director is in (e.g., HDG, NAV, GPSS, ALT, VS, FLC, APR) and verify mode changes on the annunciator.
- Data entry. Errors in the flight plan, altitude bug, or barometric setting propagate through the entire display.
- Scan technique. Tapes scroll opposite the direction of motion (airspeed numbers move down as you accelerate), which can confuse pilots transitioning from round dials. A disciplined scan — attitude, then airspeed/altitude, then heading, then back to attitude — remains essential.
- Failure recognition. Red X's overlay any tape or instrument whose source data is invalid. A yellow X or amber annunciation warns of degraded but usable data.
FAA AC 61-136 establishes pilot qualification guidelines for Technically Advanced Aircraft (TAA), defined as airplanes with an IFR-certified GPS, a moving map, and an integrated autopilot. Logging 10 hours of TAA time is one path to satisfying the commercial complex/TAA aeronautical experience requirement of 14 CFR 61.129(a)(3)(ii).
Pilots transitioning to glass should expect roughly 10-15 hours of focused training to develop proficiency in normal operations and another block of training devoted purely to abnormal/emergency procedures — particularly partial-panel flight using the standby instruments after an AHRS or PFD failure.