The ND and FM Outputs

The ND's own symbology belongs to ATA-31; this article is the backstage rulebook — what the FM sends to the ND, and by what rules: why things appear, disappear, change colour, and occasionally look wrong. The one-sentence thesis: the ND is the FM's painting; the MCDU is only the painter's hand.

1. Two data groups, one canvas, one switch

The thesis, in the AMM's own words. Per AMM 22-75-00:

*** ...B. Effects of MCDU Failure If an MCDU failure occurs on a given side (1 or 2) or if an MCDU is turned off via its BRT knob, the inhibition of background data and display of MAP NOT AVAIL on the respective ND will not result. As long as the transmitting FM (as determined by the SWITCHING/FM selector switch) is healthy, transmission to the EIS continues despite the loss of an MCDU.*

A dead or switched-off MCDU does not blank the map — the keyboard broke, not the painter (article 03's independence, display face). The FM sends two data groups: dynamic (position, wind, ground speed, track, VDEV, GPS PRIMARY status, tuned-navaid parameters, V1/VR/DH/MDA…) and map background (plan lines, points, symbols). Background is clipped to an edit area — the viewfinder: ARC a range-scaled rectangle (roughly 10.5–320.5 NM ahead, 3.5–112 behind, 8.3–265.6 abeam by range); ROSE-NAV an aircraft-centred rectangle; ROSE-VOR/LS has no edit area (background reduces to the mode legend, dynamic data still flows); PLAN a true-north-up square centred on the MRP. The MRP follows the MCDU: with the F-PLN page displayed, it is the fix on line 2L (page through the plan and the map walks with you); on other pages, the TO waypoint; indeterminable, the present position. Invalid FCU mode/range inputs drop the display to the default ROSE-NAV at 80 NM.

The FM source selector's display effects. Per AMM 22-75-00:

If BOTH ON 1 is selected, both NDs, via related DMCs, display EIS data from FM1 only. ... the NDs can only reflect the MCDU page orientation and the FCU range, mode, and option selections on the side corresponding to the selected FM. MCDU page slewing and FCU display selections on the side opposite the switch have no effect on the respective side ND. … If an FM is failed and this FM is selected to drive its onside (or both) ND(s), then the corresponding ND(s) does not receive EIS data and, thus, displays MAP NOT AVAIL.

At BOTH ON 1, both NDs follow FM1 — including whose MCDU page-turning and whose panel selections they obey; the opposite side's slewing and knob-turning do nothing (exception: each DMC reads its own EFIS mode selector, so ROSE-VOR/LS/ENG overrides the FM background locally). And there is the true meaning of MAP NOT AVAIL: the FM selected to drive that ND is dead — move the selector to the healthy FM and the map returns (article 19's SINGLE mode, in pictures). In backup navigation (NORM-only — article 19), the MCDU itself feeds both data groups to the EIS, the FM stops transmitting even if healthy, and on exit the FM rebuilds its background buffer before resuming.

2. The plan-display master rules

Per AMM 22-75-00:

There are four F-PLN configurations for which data are transmitted: ACTIVE, SECONDARY, TEMPORARY and the dashed F-PLN. These configurations are transmitted only for ARC, ROSE-NAV or PLAN mode. … - All idents and symbols associated with a terminal area procedure except for the last waypoint in a departure or the first waypoint in an arrival are not transmitted if an enroute range is selected, unless the waypoint is the active waypoint or the MRP.

Four plan configurations, three map modes — and automatic decluttering: at en-route ranges (160/320 NM) terminal-procedure fixes vanish wholesale (keeping the departure's last point, the arrival's first, the active waypoint and the MRP; origin and destination always draw). SID/STAR fixes "disappearing" at long range is range-class filtering, not a lost plan — wind back inside 80 NM and they return. A leg makes the edit area if either end is inside the frame, or any part of it crosses the frame.

3. The nine-colour line chart

The official summary table. Per AMM 22-75-00:

Flight Plan Color primary flight plan green continuous alternate flight plan cyan dashed missed approach cyan continuous offset path green dashed engine-out SID yellow continuous SECONDARY flight plan white dimmed continuous TEMPORARY flight plan yellow dashed dashed F-PLN green dashed abeam/radial cyan dashed

Active = solid green; alternate = dashed cyan; missed approach = solid cyan; the offset's original path = dashed green; EOSID = solid yellow; SEC = dimmed solid white; TMPY = dashed yellow; the "dashed F-PLN" = dashed green; abeam/radials = dashed cyan. The dashed F-PLN's mechanism (the source of article 24's "the plan dims in HDG"):

- If FM LATERAL AUTOCONTROL (Nav) is neither armed nor engaged and ARC or ROSE NAV mode is selected, the ACTIVE flight plan vectors are transmitted under the DASHED F-PLN label. ... - If FM LATERAL AUTOCONTROL is armed but the current A/C track will not intercept the active leg, operation is per the rules above. In all cases, the ACTIVE flight plan is not transmitted.

NAV neither armed nor engaged → the active plan re-labels itself dashed. And sharper: NAV armed but the present track will not intercept the active leg → still dashed — arming is not capturing, and the dashes are telling you "flown like this, you won't join". Armed and intercepting draws the solid curved capture path (the pre-NAV picture of articles 09/23).

4. Who appears when

• ACTIVE primary: always transmitted in ARC/ROSE-NAV; in PLAN too, except when the onside MCDU is on a SEC page whose plan cannot be co-strung — SEC takes the stage.
• Alternate and missed-approach segments: drawn in ARC/ROSE-NAV only while the onside MCDU is paged to them (PLAN: when the MRP is one of their fixes). The missed approach normally stays off the map — page the MCDU to it during the briefing and the solid cyan appears. A practical trick, not a fault.
• The OFFSET label swap (article 21's solid/dashed greens, explained). Per AMM 22-75-00:

The offset path is transmitted as the ACTIVE primary flight plan vectors. The original active path is transmitted as the offset path vectors.

The offset wears the "active" badge (solid green), the original wears "offset" (dashed green) — the solid line is always the one to be flown, achieved by swapping name-tags (waypoint symbols stay on the original; the offset distance rides as an ident; deletion swaps back, the original transiting through a temporary label).

• EOSID (solid yellow), a small state machine: drawn in preflight when one exists; drawn in PLAN even before an engine-out (for study); after EO activation — past the divergence point it is drawn as the active plan, before it as a TMPY (awaiting your confirmation or deletion); once inserted, active in all modes.
• SEC (white): transmitted as one package (unlike ACTIVE's segments), only while the onside MCDU is in the SEC page hierarchy — and legs coincident with ACTIVE are not double-drawn (ACTIVE wins).
• TMPY (dashed yellow): follows the ACTIVE-primary rules; the priority chain runs ACTIVE primary → TMPY → missed approach → TMPY missed approach; while revising the alternate, an existing alternate line outranks the TMPY.
• FIX INFO's dashed cyan (article 21): radials draw even when the reference fix is outside the frame; an intercept point, once inserted, sheds the dashes and becomes an ordinary waypoint; a typed radial draws regardless of interceptability, the abeam tracks the MCDU line's state.
• DIR TO's transient vectors: a chosen fix draws a yellow aircraft-to-fix vector; a manually entered RADIAL IN/OUT (≤ 160°) replaces it with a transient radial; the default-offered RADIAL IN is not drawn; the 1R/2R fields are mutually exclusive (entering one clears the other).

5. Points and symbols — unique transmission and the five buttons

Waypoints transmit once: a fix appearing in several plans draws once, by priority. The active waypoint's four exceptions: if it is an NDB, a navaid or an airport it wears that symbol instead — and if it terminates an FM/VM leg no symbol is drawn at all (a MANUAL leg's "no endpoint", made visible — article 21). Pseudo-waypoints ride only the ACTIVE plan (on the offset path when one exists); required-distance-to-land and friends travel the dynamic channel. Runways draw to scale (paved length, oriented) at terminal ranges, and shrink to a symbol plus true bearing at en-route ranges. The airport's two identities. Per FCOM DSC-31-45:

Airport included in the flight plan: ‐ If the runway is not specified, the airport is indicated by a star and the identification is displayed in white ‐ If the runway is specified, it is indicated by an oriented runway symbol in white. ... The airports that are not displayed as part of the flight plan may be displayed (ARPT pb on the EFIS control panel). They are indicated by a star and the identification in magenta.

White = in the plan (star without a runway, oriented runway strip with one); magenta star = an ARPT-button guest — colour is identity.

The five option buttons (WPT/VOR.D/NDB/ARPT/CSTR — one at a time, article 02): when the buffer cannot hold every selected facility, the ND says so with a message; WPT filters by range class — terminal ranges draw terminal-class fixes, en-route ranges en-route-class fixes ("I pressed WPT and the point still isn't there" is usually a class mismatch); VOR.D does not duplicate already-tuned stations; CSTR shows constraints (window constraints stacked two-high) plus constant-Mach segments (the .XX below any speed constraint) and, at en-route ranges, the grid MORA; tuned ILS/MLS stations draw no symbol at all (declutter). Holds and procedure turns draw their full computed circuit only at terminal ranges on the active or next leg (direct entries draw no entry transition; teardrop/parallel do); sizing uses a 210 kt CAS default without predictions, the predicted speed with them — and once active, the circuit re-sizes at each fix passage on current CAS (the pattern "breathes"); alternate-segment holds never draw.

6. Response times — and honest distortion

The book's own ceilings for a lateral revision reaching the map: DIR TO, waypoint insertion, PPOS holds — 1.5 s; offsets — 2.0 s; ACTIVATE SEC, NEW DEST, airways — 5.0 s. Give the picture five seconds before suspecting the system. And one admitted lie: per AMM 22-75-00, for long great circle path legs, the display is distorted — the ND draws with a simplified earth model, so very long legs bend on the screen. A crooked line is not crooked navigation — XTK is the truth (article 23). The active leg is transmitted in three independently-edited pieces (turn-in, body, turn-out) precisely to keep long legs from making the picture jump.

7. Operating the picture

The MAP NOT AVAIL troubleshooting tree (sections 1 plus article 19): check the FM source selector's position → is the selected FM dead? → try the manual FM reset (one at a time — article 29) → still dead, check POSITION MONITOR's IRS/GPIRS positions → position valid, activate backup navigation. The key discrimination: a dark MCDU never costs the map; a lost map is an FM-side problem.

Three briefing tricks (the rules, applied): PLAN mode with the F-PLN page walks the route fix by fix (the MRP follows line 2L); page the MCDU to the missed approach and the solid cyan line joins the briefing; whether the SEC contingency draws depends on your MCDU being on a SEC page — the white line is paged into existence. Interfaces: CHECK NORTH REF and the magenta CORR (article 20); offset and FIX INFO handling (article 21); transition-geometry recursion (article 23); pseudo-waypoint semantics (article 24) — this article is their picture-rules layer.

[!warning]- Four misconceptions this article corrects (1) Switching an MCDU off does not blank the ND — MAP NOT AVAIL means the selected FM is dead; the fix is the source selector or an FM reset, not the keyboard. (2) Dashed green with NAV armed is a warning, not a formality — the present track will not intercept the active leg; arming is not capturing. (3) SID/STAR fixes vanishing at 160/320 NM is range-class decluttering, and a WPT-button point that won't appear is usually the same filter — think knife before fault. (4) The solid line is always the path to be flown — in an offset the system swaps the labels rather than restyling the lines, so you never need to memorise "is offset solid or dashed".

Self-test

[!note]- Q1. The two FM-to-ND data groups — and what background survives in ROSE-VOR?

Dynamic data (position, winds, VDEV, GPS PRIMARY status, tuned navaids, V-speeds…) and map background (plans, points, symbols). ROSE-VOR/LS has no edit area: background reduces to the mode legend while dynamic data continues.

[!note]- Q2. Does switching off the onside MCDU raise MAP NOT AVAIL — and what does?

No — background continues while the transmitting FM is healthy. MAP NOT AVAIL appears when the FM selected to drive that ND has failed.

[!note]- Q3. After BOTH ON 1, what can the right-side panels still change — and what not?

The right DMC still honours its own EFIS mode selector (ROSE-VOR/LS/ENG override locally). But MCDU page-slewing and FCU range/mode/option selections on the right have no effect — both NDs reflect the FM1 side's selections.

[!note]- Q4. Recite six lines of the nine-colour chart — and which line is solid green after an offset?

Active solid green; alternate dashed cyan; missed approach solid cyan; offset original dashed green; EOSID solid yellow; SEC dimmed white; TMPY dashed yellow; dashed F-PLN dashed green; abeam/radial dashed cyan. After an offset, the offset path is the solid green — it carries the active label.

[!note]- Q5. NAV is armed and the plan is still dashed — what is that telling you?

The current track will not intercept the active leg. Fix the geometry (heading, or DIR TO) — the armed NAV will otherwise never capture.

[!note]- Q6. How do you get the missed approach onto the map — and SEC's appearance conditions?

Page the onside MCDU to the missed-approach segment (or, in PLAN, put the MRP on one of its fixes). SEC draws while the onside MCDU is in the SEC page hierarchy, as one package, with ACTIVE-coincident legs not double-drawn.

[!note]- Q7. In what identities is the EOSID drawn before and after the divergence point once EO is active?

Past the divergence point: as the ACTIVE plan. Before it: as a TMPY, awaiting confirmation or deletion. (Inserted, it is active everywhere; pre-EO it draws in preflight and PLAN for study.)

[!note]- Q8. Two reasons a point stays hidden with WPT selected?

Range-class filtering (terminal-class point at an en-route range, or vice versa), or the display buffer is full (the ND announces the overflow).

[!note]- Q9. What speed sizes a drawn holding circuit — and when does it "breathe"?

210 kt CAS by default, the predicted speed once predictions exist — and after the hold becomes active, it re-sizes at each fix passage on current CAS.

[!note]- Q10. How long may ACTIVATE SEC take to repaint — and does a bent long-haul leg mean bad navigation?

Up to 5 s (1.5 s for DIR TO/insertions, 2 s for offsets). No — long great-circle legs draw distorted on the simplified earth model; XTK remains the truth.

Key takeaways

References

MCDU-failure effects, data groups, edit areas and MRP rules, fallback defaults, FM-selector display effects with MAP NOT AVAIL, backup-navigation display switching and response times per AMM 22-75-00 §1 (the failure and selector passages quoted verbatim); plan-configuration rules, the colour table, dashed-plan mechanism, per-plan appearance conditions, the offset label swap, EOSID states, unique transmission with the active-waypoint exceptions, runway/airport drawing, option-button filters and hold-drawing rules per AMM 22-75-00 §2 (the master rules and colour table quoted verbatim; the remainder attributed summary of the description text). Airport symbology per FCOM DSC-31-45. The troubleshooting tree and briefing tricks are integrative syntheses.

Independent study material, not an Airbus publication and not endorsed by the manufacturer. Always defer to the current operator FCOM, FCTM, and QRH for operational use.