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