Electronic Flight Instrument Systems (EFIS): PFD/ND Modes and Standby Logic

022-13-03Pablo Asensio Martínez2026-03-272 min

EFIS replaces electromechanical instruments with CRT or LCD screens. The system typically consists of two main displays for each pilot: the PFD (Primary Flight Display) and the ND (Navigation Display).

Primary Flight Display (PFD)

Combines the "Basic T" flight instruments into a single dynamic display.

  • Layout:
    • Center: Attitude Indicator (AI) with Flight Director (FD) bars.
    • Left: Airspeed Indicator (Speed Tape). Includes speed bugs ($V_1$, $V_R$, $V_2$), trend vectors, and Mach number.
    • Right: Altimeter (Altitude Tape) and Vertical Speed Indicator (VSI).
    • Bottom Center: Heading/Track indication (Compass Rose segment).
    • Top: FMA (Flight Mode Annunciator) - Displays Autopilot/Autothrust status.
  • Radio Altimeter: Displayed below 2500 ft AGL.

Navigation Display (ND) / EHSI

The ND displays navigation data and can be operated in various modes selected via the EFIS Control Panel.

Common Display Modes

Mode Description Orientation Features
MAP / ARC Expanded view (~90° arc). Moving map. Heading or Track Up Waypoints, Flight Plan, Weather, Terrain, Traffic. Most common flight mode.
VOR / ROSE Full 360° compass rose. Heading Up VOR deviation bar (RMI style). Aircraft in center.
APP / ILS Full 360° or Expanded. Heading Up ILS (Loc/GS) deviation.
PLAN Static map. True North Up Used to review the flight plan (step through waypoints). No Weather/Terrain.

Centre (CTR) vs Expanded (EXP)

  • CTR (Full Rose): Aircraft symbol in the center. 360° view.
  • EXP (Expanded/Arc): Aircraft at bottom. Forward view sector. Use for better forward resolution.
  • Weather Radar (WXR): Typically cannot be displayed in Full Rose VOR/ILS or PLAN modes. Requires an Expanded/Map mode.

EFIS Control Panel

Allows the pilot to select:

  • Mode: MAP, VOR, APP, PLAN.
  • Range: e.g., 10, 20, 40, ... 640 NM.
  • Overlays: WXR (Weather), TERR (Terrain), TFC (Traffic), WPT (Waypoints), ARPT (Airports), STA (Navaids).
  • Baro Setting: QNH/STD.

Standby Instruments (ISIS)

In case of total EFIS failure, Standby Instruments are required.

  • ISIS (Integrated Standby Instrument System): A single small electronic display combining Attitude, Altitude, and Airspeed.
  • Independence: Operates from independent pitot/static sources, gyros, and power supplies.
  • Challenges: Often larger parallax errors, smaller size, and harder to read than main displays.