RNP and PBN Operations

Performance-based navigation turns "navigation performance" into a contract: every airspace names a number, and the aircraft proves itself against it with article 20's EPU/RNP machinery. This closing article walks the family from widest to narrowest, ending at RNP AR — the most equipment-hungry operation in the book. (The baseline airframe carries RNP AR below 0.3 and GPS PRIMARY — article 01.)

1. The family map — and the two criteria

Per FCOM PRO-SPO-51:

The Performance Based Navigation (PBN) concept implies that the aircraft follows the defined track with a requested navigation performance. The PBN includes RNAV and RNP operations.

RNAV specifications carry no onboard-monitoring requirement; RNP specifications do — RNP's essence is the aircraft knowing, and announcing, when it doesn't know (article 20's integrity criterion). Approvals are airspace-by-airspace from the authority, with the AFM stating compliance. The two universal criteria:

Before the aircraft enters an RNAV/RNP airspace, RNAV/RNP capability is based on: ‐ The required RNAV/RNP equipment that is described in each RNAV/RNP section of the FCOM ‐ Navigation Accuracy HIGH displayed on the MCDU PROG page ‐ Any specific local requirements published in the Aeronautical Information Publication (AIP). When the aircraft flies in RNAV/RNP airspace, RNAV/RNP capability is based on: ‐ Navigation Accuracy HIGH...

Check three at the door (equipment list, PROG-page HIGH, AIP specials); inside, watch only HIGH — equipment is the ticket, accuracy the pass. The equipment lists, collated:

Three lines of pattern: oceanic wants the pairs (dual FMGEC/MCDU, or one plus backup navigation — article 19's legal standing); terminal wants the FD (guidance precision by the bars); AR wants everything — the longest list on the aircraft, and the root of the MEL's AR-sensitivity surface (article 32).

2. The oceanic family — accounting in time and position

RNAV 10's GPS clause is a time account. Per FCOM PRO-SPO-51:

‐ One GPS if the flight time outside radio navaid coverage is longer than: ‐ 6.2 hr from the time of IRS ground alignment, or ‐ 5.7 hr from the time of the last FM position update.

Pure inertia's drift budget (article 20's segmented EPU growth) buys exactly that much coverage-free flying. And the degraded case:

If the GPS PRIMARY LOST message is displayed on both NDs/MCDUs, RNAV 10 operations can be continued: ‐ With no time restriction if radio navaids update is available ‐ For 5.7 hr from the time of the last position update if radio navaids update is not available. After 5.7 hr, the navigation accuracy must be considered LOW regardless of the navigation accuracy that is displayed on the MCDU PROG page.

Both sides lost: with radio updating, no time limit; without, 5.7 hours from the last update — and past that, treat the accuracy as LOW whatever the PROG page displays. The screen can lie (the EPU model runs out of honesty); the clock cannot — one of the book's rare "trust the watch over the instrument" clauses.

The generic degradation tree (each section repeats it; learn it once): one side GPS PRIMARY LOST / NAV ACCUR DOWNGRAD → continue on the healthy FMGEC. Both sides, or the position-difference family → triangulate on POSITION MONITOR + the IRS page + GPS MONITOR to find who is right → fly that side. Both sides DOWNGRAD → note that the FMS's default required accuracy (2 NM cruise / 1 NM terminal) can be stricter than the airspace — relaxing the value to the airspace figure is crew discretion, and it goes back to default on leaving; still downgraded → report the capability loss to ATC.

3. The terminal family — and database discipline

Per FCOM PRO-SPO-51:

The flight crew must crosscheck the terminal procedure from the published charts with the FMS navigation database on the F-PLN page (waypoint sequences, tracks, distances, and altitude or speed constraints). The flight crew must not modify the procedure that is provided by the navigation database, unless required by the ATC (DIR TO radar vectoring, insertion of waypoints from the navigation database).

Chart-against-database on four counts (sequence, tracks, distances, constraints) — and the procedure is not yours to edit: the only two exceptions both come from ATC (a DIR TO under vectors, and insertion of database waypoints). RNP 1 adds the pre-departure RAIM/AIME prediction — GPS PRIMARY availability forecast (articles 20/33).

4. The APCH/AR watershed

RNP APCH (=RNAV(GNSS)): the short list above, and the flying is simply the FINAL APP card (articles 11/30). RNP AR is another world. Per FCOM PRO-SPO-51:

For RNP AR operations, the flight crew should refer to the specific procedures published by the airline. The airline must obtain an operational approval and the flight crew must be qualified for this type of operations. To obtain this operational approval the airline should refer to the AFM and the associated Airworthiness Compliance Document (ACD).

Three locks, none of them on the aircraft: the airline's procedures, the operational approval, the crew's qualification — with the technical basis in the ACD (article 33's "refer to ACD"). The FCOM gives the trunk steps only; it does not excuse the airline from writing the detail. The equipment deltas decode mechanically: dual GPS receivers (in the MMRs), three ADIRS, both PFDs with lateral/vertical deviation — AR's containment is so narrow that one dead display leaves you unable to prove you are on the path; the two-AP requirement bites only below 0.3 NM or with a missed approach below RNP 1 (the baseline airframe carries the below-0.3 fit — plan on both APs); and the TAWS terrain display makes the list because AR procedures habitually thread mountains.

5. The AR profile — the trunk steps

Per FCOM PRO-SPO-51:

The availability of GPS PRIMARY for the estimated time of operation must be verified with an appropriate GPS prediction tool before dispatch. Prior to starting RNP AR instrument procedures, check that: ‐ OAT and wind, as applicable, are within limits ‐ The FMS lateral and vertical F-PLN extracted from the navigation database is in accordance with the instrument procedure chart ‐ Two GPS sensors are in NAV or SBAS on GPS MONITOR page ‐ The correct RNP value is displayed on MCDU with HIGH accuracy ‐ GPS PRIMARY is available.

Dispatch: the GPS prediction tool. Before the procedure, five checks: OAT/wind in limits (temperature bends barometric altitude, and with it the vertical containment); both axes of the plan against the chart; two GPS sensors NAV/SBAS on GPS MONITOR; the right RNP value with HIGH; GPS PRIMARY present. With obstacles, terrain on both NDs (unless one side needs the radar); and speed/configuration matched to the procedure's turn radii (article 23's constant-radius legs — too fast and the radius won't close). The departure:

DEPARTURE Before takeoff, check that NAV is armed. When NAV is indicated active on FMA and at 100 ft, select AP ON. Monitor lateral deviation using the XTK on ND. Callout must be performed when XTK is at or above 0.1 NM. If XTK increases towards 1 RNP, take over manually using FD indication to fly back on the intended flight plan and using ND and XTK to reengage AP as applicable.

NAV armed before takeoff (a preset disarms it — article 30); NAV active plus 100 ft → AP ON, as a legal requirement, not a comfort (article 05); XTK watched, 0.1 NM is the callout line; XTK growing toward one full RNP → take over manually on the FD, fly back onto the plan, re-engage when re-established. (A parallel configuration text monitors the PFD's L/DEV against ½ dot — the baseline airframe's PFDs carry L/V-DEV, so both dialects exist; the airline's procedure decides.) The approach runs the RNAV(RNP) FINAL APP card (articles 11/13: navaid deselection, GPS PRIMARY on both FMs, both GPS in NAV, TERR as required, FINAL APP checked at the FDP, XTK > 0.1 / V-DEV > ½ dot callouts); the go-around runs article 14 — with the AR reading of the TCAS split (FINAL drops, NAV stays: the lateral containment survives the RA).

6. AR engine-out — the manual's rare training clause

Per FCOM PRO-SPO-51:

In the case of engine failure during departure or a missed approach procedure, the flight crew must consider the bank angle limitation when flying at a speed below the maneuvering speed. Turns in the procedure may require bank angles above 15 °. Flying with one engine inoperative affects the aircraft lateral performance. The flight crew should be trained and instructed to disconnect AP if the aircraft deviates from the intended track. This training must consider turning and straight legs as appropriate.

The collision of two schedules: engine-out bank is capped at 15° below manoeuvring speed (article 06/19), while the procedure's turns may demand more than 15° — single-engine lateral performance may not close the turn. Hence the manual's unusual step of writing training into a procedure: crews must be trained to disconnect the AP and fly back to the track by hand when it deviates, on straight and turning legs alike. The inversion to notice: everywhere else the doctrine is "use the AP when you can"; AR engine-out reverses it — when the AP can't hold the turn, the human is the last lateral margin. Contingency detail beyond this lives in the ACD-to-airline chain (the FCOM: detailed information is provided in the ACD for the airline to develop contingency procedures) — this series stops where the company card begins.

7. The whole chain — and the series' last word

A full AR approach, as a replay of the entire book: dispatch (GPS prediction + the MEL's three questions — article 32) → the five checks late in cruise (§5) → DECEL sequences the phase (article 22; high-elevation procedures activate it by hand) → APPR pushbutton (article 11's six FINAL APP conditions) → FINAL APP confirmed at the FDP with the blue arrow (article 11) → XTK callouts valid mid-turn (article 23's arc definition) → GPS PRIMARY LOST → go around unless visual (article 20's QRH branch; AR gets no "value-plus-HIGH" continuation waiver) → missed approach in NAV (article 14). Every link in that chain is a section of the preceding thirty-three articles — PBN is the final exam.

The GPS PRIMARY LOST family layers, disambiguated: RNAV 10 — the time account (5.7 h); RNAV 5/1/2 and RNP 1/2/4 — report the capability loss to ATC (the value-plus-HIGH continuation cases are article 33's); RNP APCH/AR on approach — go around unless already visual.

[!warning]- Four misconceptions this article corrects (1) Past 5.7 hours without updating, a HIGH on the PROG page is not to be believed — the accuracy is LOW by decree; trust the clock over the screen. (2) A terminal procedure from the database is not editable — the only two exceptions are ATC-driven (vectors/DIR TO, database-waypoint insertion). (3) RNP AR capability is one-third aircraft — the airline's procedures, the operational approval and the crew qualification are the other locks; a below-0.3 fit alone authorises nothing. (4) AR engine-out inverts the automation doctrine — the AP may be unable to hold the procedure's turns at the engine-out bank schedule, and the trained response is to disconnect and hand-fly back.

Self-test

[!note]- Q1. The three door checks before PBN airspace — and the one thing watched inside?

Equipment per the specification's list; navigation accuracy HIGH on PROG; AIP local requirements. Inside: HIGH.

[!note]- Q2. RNAV 10's two GPS time limits — and is a HIGH display after 5.7 hours credible?

GPS required beyond 6.2 h from IRS ground alignment or 5.7 h from the last position update, outside navaid coverage. No — past 5.7 h without updating, accuracy is considered LOW regardless of the display.

[!note]- Q3. The memory pattern for the family's equipment lists?

Oceanic wants the pairs (dual FMGEC/MCDU or one plus backup navigation); terminal wants the FD; AR wants everything.

[!note]- Q4. With both sides showing NAV ACCUR DOWNGRAD, may the required accuracy be changed — and what happens on leaving the airspace?

The FMS default (2/1 NM) may be stricter than the airspace; relaxing it to the airspace value is crew discretion — and it must go back to the default on exit. Still downgraded: report the capability loss to ATC.

[!note]- Q5. The two lawful modifications to a database terminal procedure?

Both from ATC: a DIR TO under radar vectoring, and insertion of waypoints from the database.

[!note]- Q6. The equipment deltas from RNP APCH to RNP AR — and when are two APs required?

AR adds the second FMGEC/MCDU/FD, dual GPS in the MMRs, three ADIRS in NAV, both PFDs with L/V-DEV, TAWS terrain display (and keeps both FCU channels, one FWC). Two APs: RNP below 0.3 NM, or a missed approach below RNP 1.

[!note]- Q7. The five pre-procedure AR checks?

OAT/wind within limits; the FMS lateral and vertical plan against the chart; two GPS sensors NAV/SBAS on GPS MONITOR; the correct RNP value with HIGH accuracy; GPS PRIMARY available. (Dispatch adds the GPS prediction tool.)

[!note]- Q8. The AR departure's takeover criterion — in both dialects?

XTK at/above 0.1 NM is the callout; XTK growing toward one full RNP → manual takeover on the FD, back to the plan, re-engage. The parallel text monitors PFD L/DEV against ½ dot — the airline's procedure chooses the dialect.

[!note]- Q9. Why does AR engine-out demand "disconnect on deviation" training?

Engine-out bank is limited to 15° below manoeuvring speed while AR turns may need more — the AP may not close the turn. The trained answer: disconnect, hand-fly back onto the track, on turning and straight legs.

[!note]- Q10. GPS PRIMARY LOST in RNAV 10, RNP 2, and RNP AR — the three responses?

RNAV 10: the time account (unlimited with radio updating, 5.7 h without). RNP 2 (and the RNAV/RNP en-route family): report the capability loss (continuation cases per the limitations). RNP APCH/AR on approach: go around unless visual.

Key takeaways

References

PBN definitions, entry/in-airspace criteria, per-specification equipment lists and procedures, the RNAV 10 time accounting, degradation trees, terminal database discipline, the RNP AR locks, checks, departure monitoring (both dialects) and the engine-out training clause per FCOM PRO-SPO-51; RNP accuracy and AR/ACD clauses per FCOM LIM-AFS (article 33); the RNAV(RNP) approach card per a representative operator QRH (articles 11/13); option fits per one representative airframe's options list. The chain replay and the family-layers table are integrative syntheses.

And with that, the ATA-22 series closes where it opened: everything in this chapter reduces to two questions — does the aircraft know where it is, and does it know when it doesn't? PBN merely wrote those questions into law.

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.