10.3 Cockpit Symbology, Colour Standards and Display Reversion
Key Takeaways
- Cockpit colour language treats red as warning or failure requiring immediate action, amber as caution or disagreement, green as normal, valid or engaged, cyan as selected or armed targets, and magenta as FMS command or the active route.
- PFD attitude symbology is a pictorial ADI: blue sky, brown ground, pitch ladder, roll scale and pointer, aircraft reference symbol, flight-director bars, and speed and altitude tapes with an FMA across the top.
- ND heading symbology is a pictorial HSI: compass rose or arc, selected heading and track, course deviation, bearing pointers, and, in map modes, the active route with weather, traffic or terrain overlays.
- If a PFD display unit fails, the PFD image is transferred onto the adjacent ND, often in a compact or combined format; attitude, speed and altitude take priority over the map.
- Display-computer switching and ATT/HDG or air-data source select restore a usable picture after a processor or sensor-channel failure; comparator monitors flag left/right mismatch, and DU swap is used to isolate a failed head.
10.3 Cockpit Symbology, Colour Standards and Display Reversion
Once a CRT, LED matrix or LCD can paint a pixel, the certifying engineer still has to recognise what the pixel means and where the picture goes when a unit fails. That is a practical level-1 development of the broad current headings 5.1 and 5.15, using the former detailed cockpit-layout and EFIS examples: colour conventions, the attitude and heading symbols that stand in for the old ADI and HSI, and the reversion, compact and display-swap paths that keep a usable PFD in front of at least one pilot. Engine-warning colour on EICAS or ECAM follows the same red/amber/green language but is not duplicated here; this section stays with flight-instrument symbology and display-path reversion.
Colour Conventions
Transport EFIS palettes follow a common operational language even though exact hues differ between manufacturers. Treat colour as meaning, not decoration.
| Colour | Typical meaning on PFD, ND and associated alerting | What it tells the engineer |
|---|---|---|
| Red | Warning, failure, exceedance, immediate crew action (stall, engine fire, PULL UP, an invalid but critical flag) | A steady red ATT or SPD flag is not a nuisance light; the selected sensor or the comparator has declared the data unusable |
| Amber / yellow | Caution, abnormal, disagreement, an approaching limit | An amber heading or airspeed mismatch points to a split between left and right sources, not automatically to a failed LCD |
| Green | Normal, valid, engaged autopilot or autothrust mode, captured localiser or glideslope on some types | Loss of a green engaged FMA with white or cyan armed modes is a mode or autopilot issue, not necessarily a DU fault |
| White | Scales, labels, some armed modes, inactive legends | Structure of the instrument face |
| Cyan | Selected values (selected heading, selected altitude, selected speed), sky shading, some armed modes | Cyan bugs are crew targets from the FCU/MCP; if they freeze, look at that control interface to the EFIS computer |
| Magenta | FMS active route, commanded flight-director or flight-path cues, some managed targets | A magenta map that disappears while heading remains is often an FMS input, not a failed DU |
| Blue (sky) | Attitude-sphere sky | Sky and ground colours that invert or wash out on one DU suggest that DU’s polariser, backlight or raster path |
| Black | Background | A black rectangle where a tape should be is a flagged parameter, not successful declutter |
LED annunciator captions on the glareshield and pedestal use the same red/amber/green language even when they are discrete diodes rather than EFIS pixels. A red master-warning caption is still a warning; an amber master-caution caption is still a caution.
[!WARNING] Do not reverse red and amber. Red is the highest-priority failure colour. Display software that painted warnings in amber, or cautions in red, would violate the alerting philosophy the crew is trained on. Changing palette files in the field would be an unapproved software change under heading 5.13, not a local colour preference.
Attitude and Heading Symbology
The PFD attitude picture is a pictorial ADI:
- A brown ground / blue sky sphere or ribbon with a white horizon line.
- A pitch ladder marked in degrees, often compressed at extreme pitch so that a recovery attitude remains readable.
- A roll scale (commonly 10°, 20°, 30°, 45°, 60°) and a roll pointer or sky pointer.
- Aircraft reference: a fixed chevron or split-bar symbol in the centre of the display.
- Flight-director command bars (V-bars or cross-bars) or a flight-path vector, in magenta or green depending on type.
- A slip/skid indicator (the electronic analogue of the inclinometer) under the roll pointer.
- Radio altitude as a numeric, with a rising-runway or expanding height cue, and localiser/glideslope deviation scales in the lower attitude area during approach.
Around the sphere sit the airspeed tape (left), altitude tape and vertical-speed indication (right), a heading or track tape (bottom), and the FMA (top). Fail flags replace a tape with a red or amber ATT, SPD, ALT or HDG caption when the source is invalid. Decision-height or minimums bugs, where selected, typically turn amber or red as radio altitude reaches the set value — another colour-as-meaning example rather than a random palette choice.
The ND heading picture is a pictorial HSI:
- Compass rose or arc, lubber line, and digital heading readout.
- Selected heading bug (often cyan) and track diamond.
- Course pointer and deviation bar for VOR or ILS in EHSI/APP modes.
- Bearing pointers for VOR or ADF.
- In MAP/ARC mode: aircraft symbol at the bottom (arc) or centre (rose), magenta active flight-plan line, waypoints, navaids, and range rings matching the selected NM range.
- Overlays: weather-radar returns, TCAS traffic (other traffic typically white, traffic advisory amber, resolution advisory red), and terrain density in green/amber/red.
Compact, condensed or combined formats (names vary by manufacturer) squeeze a small attitude sphere plus essential tapes onto a single DU when only one screen remains on that side, or when two centre pages must share one remaining engine display. The engineer should recognise compact mode as a reversionary format generated by the display computer, not as a separate LRU and not as a new sensor.
Display Reversion, Compact Modes and DU Swap
Reversion is how the heading 5.1 layout survives a failure. Three mechanisms appear on most two-crew EFIS installations.
1. Display-unit reversion (image transfer and DU swap). If the captain’s PFD unit fails, the PFD format is automatically or manually moved onto the adjacent ND unit. The full-range map is dropped or reduced. Some types allow the crew to swap PFD and ND with a PFD/ND transfer push-button so that a dim but working outboard screen can take the map while the brighter inboard screen takes attitude. Because PFD information is the higher-priority flight instrument, attitude never yields to the map in automatic logic: a single remaining DU on that side shows PFD or a compact PFD-plus-ND, not a full-range map alone.
2. Display-computer / symbol-generator reversion. If DMC 1 or SG 1 fails, a remaining computer is switched to drive the captain’s DUs. On Airbus EIS, DMC 3 is the usual spare; a DISPLAY SWITCHING selector lets DMC 2 or DMC 3 feed the left side. Both pilots may then share one processor — a degraded but flyable state — and a caution tells the crew that independence is lost. BITE isolates whether the computer, the DU, or the switching/video multiplexer is at fault. Computer reversion does not by itself fix a failed LCD heater or a failed EHT supply inside one DU.
3. Source reversion (ATT/HDG and AIR DATA). If the attitude sphere fails with a red ATT flag but the DU is otherwise alive (scales, FMA and the opposite tape still painting), the fault is the inertial/AHRS/ADIRU source or its bus, not the glass. ATT/HDG switching selects another inertial lane. Air-data switching does the same for the speed and altitude tapes. Comparator monitors between left and right PFDs generate amber disagreement messages (IAS, ALT, ATT, HDG types) when both sources are alive but not matched.
| Failure seen | First reversion to expect | What not to do first |
|---|---|---|
| One DU blank; neighbour still shows a normal PFD or ND | Image transfer to the remaining DU; then DU swap with a known-good lower-priority unit per AMM | Replace the symbol generator before proving the fault follows the DU |
| Both captain DUs flagged or blank | Captain’s computer, its power, or a source that feeds both formats | Swap only the outboard LCD and close the defect |
| Red ATT flag; tapes and ND still normal | ATT/HDG source select; interrogate IR/AHRS BITE | Replace the PFD DU |
| Amber IAS or ATT disagreement, both pictures alive | Compare left and right sources; do not assume a single DU palette fault | Recalibrate colour in software |
| Colour missing on one DU only | That DU or its cable | The opposite symbol generator |
| Colour wrong on every DU from one computer | That symbol generator’s video/palette path | Random DU swapping without BITE |
Line isolation follows the same table. After a DU swap, if the fault follows the unit, the DU is implicated; if the fault stays in the panel position, suspect wiring, cooling, or the computer output assigned to that position. Record BITE before swapping so that a latent computer fault is not hidden by a successful compact-mode take-off.
[!NOTE] PFD priority. Automatic reversion is designed so that a usable attitude, speed and altitude picture remains in front of the flying pilot. When you find a cockpit already in compact mode, treat it as evidence of a DU or computer failure that the system has already managed, then interrogate EFIS BITE rather than cycling displays at random.
Worked reversion scenario. The captain’s outboard AMLCD goes black with no edge glow (backlight dead). Automatic logic paints the PFD on the inboard DU in compact format: a reduced attitude sphere, speed and altitude tapes, and a small heading rose; weather-radar overlay is lost. The first officer’s PFD and ND remain independent. DISPLAY SWITCHING stays in NORM because both symbol generators are healthy. After landing, BITE on the captain’s computer reports a DU overtemperature and backlight-current fail. Swapping the captain outboard DU with the lower centre DU (same part number, AMM procedure) restores a full-size PFD on the left, and the fault follows the removed unit onto the centre position. That is display-unit reversion plus physical DU swap, not ATT/HDG source select and not an unapproved palette edit.
Category A candidates should recognise red versus amber, point to PFD versus ND, and know that a failed PFD screen moves onto the ND. B1/B2 candidates should also distinguish DU transfer, computer switching and sensor source select, and should use comparator captions to avoid changing a healthy LCD when the inertial lanes disagree.
Which statement correctly reflects typical EFIS cockpit colour conventions?
Which set of symbols belongs on the PFD attitude display rather than on a map-only ND?
If a PFD display unit fails in flight on a typical two-crew EFIS, what reversion behaviour should a maintenance engineer expect?
How do display-unit swap and source-select switching differ when restoring attitude or heading after a failure?