AFS Limitations

The MEL governs leaving with broken parts (article 32); the limitations govern the healthy system's edges. This article collects the general AFS boundaries — the autopilot minimum-use heights, the FM's certification perimeter, the RNP accuracy table, the NAV-mode usage conditions, and the database-validation grades. (CAT II/III limits live in article 12, the autoland envelope in article 13.) One FCTM sentence frames the whole file. Per FCTM AOP-30-10:

The AP has not been certified in all configurations, and its performance cannot be guaranteed. If the pilot chooses to use the AP in such circumstances, extra vigilance is required, and the AP must be disconnected, if the aircraft deviates from desired or safe flight path.

In abnormal configurations the AP is borrowed, not warranted — extra vigilance, and disconnect on deviation. Every line below is that sentence made specific.

1. How low may the AP fly — the full table

Per FCOM LIM-AFS-10 (rows quoted, assembled):

At takeoff 100 ft AGL and at least 5 s after liftoff … In approach with FINAL APP, V/S or FPA mode 250 ft AGL … In circling approach 500 ft AGL … ILS approach when CAT1 is displayed on the FMA 160 ft AGL … ILS approach when CAT2 or CAT3 (single or dual) is displayed on the FMA 0 ft AGL if autoland … After a manual go-around 100 ft AGL … In all other phases 500 ft AGL

Two readings matter. 160 ft is not a DH — it is "the AP may assist down to 160 ft; below that, human hands" (a CAT I DH of 200 ft comes first; the 160 ft floor bites when the DH is lower or you want the AP longer). And the last row is the catch-all: any scenario not listed — visual manoeuvring included — defaults to 500 ft. (The CAT II manual-landing 80 ft belongs to the other limitations file — article 12.) One more approach clause:

The AP or FD in OP DES or DES mode can be used in approach. However, its use is only permitted if the FCU selected altitude is set to, or above, the higher of the two: MDA/MDH or 500 ft AGL.

OP DES disregards constraints (article 07) — so the law leashes it with the FCU window: set at or above max(MDA/MDH, 500 ft AGL).

2. Where the FM's certification ends

Per FCOM LIM-AFS-10:

FMGES lateral and vertical navigation is certified for: ‐ After takeoff, en route, and terminal area operations ‐ Navigation within RNAV/RNP airspace ‐ Instrument approach procedures (except ILS, LOC, LOC B/C, IGS, LDA, SDF, GLS and FLS final approaches) ‐ Missed approach procedures.

The FM runs the relay from after takeoff to the final-approach gate — and the "except" list is the handover roster: on every xLS-type final (ILS, LOC and back-course, IGS, LDA, SDF, GLS, FLS) the last leg belongs to the beam, not the FM (article 11's two families, in legal language). Then the three disclaimers, worth memorising verbatim:

Approval of the FMGES is based on the assumption that the navigation database is validated for intended use. Obstacle clearance and adherence to airspace constraints remains a flight crew responsibility. Fuel, time predictions/performance information is provided for advisory purpose only.

The approval assumes a validated database (section 4's grades); obstacles and airspace are forever yours, not the FM's; and the fuel/time predictions are advisory — the statutory line under article 25's credit boundary.

3. How accurate — the RNP table and the AR clause

Per FCOM LIM-AFS-10:

RNP accuracy with GPS PRIMARY is: With AP ON (1) With AP OFF and FD ON (1) With AP OFF and FD OFF En route 1 NM 1 NM 1.1 NM In terminal area 0.5 NM 0.51 NM 0.51 NM In approach 0.3 NM 0.3 NM With F-LOC deviation: 0.3 NM Without F-LOC deviation: not authorized

As a table — three columns: AP ON / AP OFF with FD / fully manual: en-route 1 / 1 / 1.1 NM; terminal 0.5 / 0.51 / 0.51 NM; approach 0.3 / 0.3 / not authorised (without a lateral-deviation display to hand-fly against). The reading: the AP flies most precisely, FD guidance costs almost nothing, and the extra 0.1/0.01 in the last column is the human hand — while a fully hand-flown RNP approach with no deviation scale is simply not authorised. (Footnote (1): NAV mode per phase, or the FLS lateral on approach — FLS not fitted on the baseline airframe.)

The RNP AR clause (article 34's limitations face): the reference is the airworthiness compliance document (ACD); the demonstrated mode set — departure in NAV, initial/intermediate in NAV or APP NAV, final in FINAL APP, missed approach in NAV, all with the AP on (two configuration texts exist — one capped at 0.3, one below 0.3 per the ACD; the baseline airframe carries the below-0.3 fit). And the degradation clause:

If GPS PRIMARY LOST is displayed on the ND, the navigation accuracy remains sufficient for RNP operations provided that the RNP value is checked or entered on the MCDU and HIGH ACCURACY is displayed.

Losing GPS PRIMARY is not losing RNP: with the RNP value checked and HIGH shown, ordinary RNP operations continue (article 20's two criteria, operationalised — RNP AR excepted, article 34).

4. When to trust NAV — usage tickets and database grades

The NAV-mode tickets. Per FCOM LIM-AFS-10:

AFTER TAKEOFF NAV mode may be used after takeoff provided that: ‐ GPS PRIMARY is available, or ‐ The flight crew checked the FMGES takeoff updating. / IN TERMINAL AREA ... ‐ GPS PRIMARY is available, or ‐ the appropriate RNP is checked or entered on the MCDU, and HIGH accuracy is displayed, or ‐ FMS navigation is crosschecked with navaid raw data.

After takeoff: GPS PRIMARY, or a checked runway update (article 20). In the terminal area, three rungs: GPS PRIMARY / RNP-checked HIGH / raw-data cross-check — the pre-GPS staircase, still lawful. For navaid-based approaches flown in NAV/FINAL APP:

‐ If GPS PRIMARY is available, the reference navaids may be unserviceable, or the airborne radio equipment may be inoperative, or not installed, provided that an operational approval is obtained ‐ If GPS PRIMARY is not available, the reference navaids and the corresponding airborne radio equipment must be serviceable, tuned and monitored during the approach.

The startling half: with GPS PRIMARY (and an operational approval), a "VOR approach" may be flown with the VOR broken — the name is VOR, the flying is GPS. Without GPS PRIMARY the classical rules snap back: station and receiver serviceable, tuned, monitored. RNAV thresholds: RNAV(RNP) = GPS PRIMARY plus operational approval; RNAV(GNSS) = GPS PRIMARY (the compatibility table is the normal-procedures reference — article 11).

The database-validation grades (article 04's conjunctions, in their statutory home):

RNAV(GNSS) APPROACHES AND APPROACHES BASED ON VOR/NDB ... must be either: ‐ Produced by an approved supplier compliant with ED76/DO200A or DAT Type 2 requirements, or ‐ Validated and approved by the Operator. / RNAV(RNP) PROCEDURES ... must be both: ‐ Produced by an approved supplier..., and ‐ Validated and approved by the Operator.

GNSS: either/or. RNP: both/and. Four words carry the whole grading. Attached note: a small track-degree difference between the MCDU and the chart may be nothing but a magnetic-variation model mismatch — no effect on the lateral path flown (article 20). (The FLS/SLS certification clauses exist in the text — not fitted on the baseline airframe; their logic is the same "GPS present, station may fail" grading.)

5. Using the boundary book

At the approach briefing, run the file's four layers as four questions: approach type → AP minimum height → who owns the final (FM or beam) → has this procedure's database been validated at the right grade. And the three-book order for any one defect or doubt: MEL first (may we go — article 32) → LIM second (how low, once gone) → the QRH capability table last (what remains, airborne — article 12).

[!warning]- Four misconceptions this article corrects (1) The CAT1 160 ft is not a decision height — it is the AP's floor; your DH usually arrives first, and visual references must already be established to ride to 160. (2) Scenarios not in the table are not unregulated — "all other phases" means 500 ft AGL, visual manoeuvring included. (3) A "VOR approach" under GPS PRIMARY may legally be flown with the VOR unserviceable (operational approval required) — and without GPS PRIMARY, the same approach demands the station serviceable, tuned and monitored. (4) A fully hand-flown RNP approach with no deviation display is not merely imprecise — it is not authorised.

Self-test

[!note]- Q1. Recite six rungs of the AP minimum-height table — and is the takeoff line one condition or two?

Takeoff 100 ft AGL and 5 s after lift-off (two conditions); FINAL APP/V-S/FPA approaches 250 ft; circling 500 ft; ILS with CAT1 displayed 160 ft; ILS with CAT2/3 displayed 0 ft (autoland); manual go-around 100 ft; all other phases 500 ft.

[!note]- Q2. The relationship between 160 ft and the DH?

Independent floors: the DH (typically 200 ft on CAT I) demands the visual decision first; 160 ft is the AP's hard floor — useful when the DH is lower or the AP is kept longer, never a substitute for the DH.

[!note]- Q3. The OP DES leash formula in approach?

The FCU selected altitude must be at or above the higher of MDA/MDH and 500 ft AGL — a window-set tether on a constraint-blind mode.

[!note]- Q4. Which final approaches sit on the FM certification's "except" list?

ILS, LOC, LOC B/C, IGS, LDA, SDF, GLS and FLS finals — the beam takes the last leg; the FM is certified through everything up to that gate, plus the missed approach.

[!note]- Q5. The approach row of the RNP table — and why is the third column "not authorized"?

0.3 NM with AP ON; 0.3 NM with FD ON; fully manual not authorised — with no lateral-deviation display there is nothing adequate to hand-fly the RNP against.

[!note]- Q6. Can RNP operations continue after GPS PRIMARY LOST?

Yes (RNP AR excepted): provided the RNP value is checked or entered on the MCDU and HIGH accuracy is displayed — accuracy without the integrity guarantee, with the checking now yours.

[!note]- Q7. The terminal-area NAV tickets, all three?

GPS PRIMARY available; or the appropriate RNP checked/entered with HIGH accuracy displayed; or FMS navigation cross-checked against navaid raw data.

[!note]- Q8. Under GPS PRIMARY, may the VOR be broken on a VOR approach — and the reverse case?

Yes — reference navaids may be unserviceable and the receivers inoperative or not installed, given an operational approval. Without GPS PRIMARY: station and receiver must be serviceable, tuned, and monitored throughout.

[!note]- Q9. The conjunction difference in database validation — and does a MagVar degree difference matter?

GNSS/VOR/NDB approaches: approved supplier or operator validation. RNAV(RNP): both… and. A small track-degree difference from magnetic-variation model mismatch does not affect the lateral path.

[!note]- Q10. The FCTM certification philosophy's two action demands?

Extra vigilance when using the AP in configurations it was not certified for — and immediate disconnection if the aircraft deviates from the desired or safe flight path.

Key takeaways

References

AP minimum-use heights, the OP DES clause, FM certification scope and disclaimers, the RNP accuracy table, RNP AR capability and the GPS PRIMARY LOST degradation clause, NAV usage conditions, navaid-based approach rules, RNAV thresholds, database-validation grades and the magnetic-variation note per FCOM LIM-AFS-10 (the CAT II/III and autoland files are article 12 and article 13). The certification philosophy per FCTM AOP-30-10. FLS/GLS/LPV rows are quoted as printed; those functions are not installed on the baseline airframe of this series. The four-question briefing frame and the three-book order 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.