All Documents | PDF version

Chapter 10. Navigation

Table of Contents

10.1. EGPWS alerts (memory item)
10.2. TCAS warnings (memory item)
10.3. RNAV downgrades
10.4. ADR faults
10.5. ADR disagree
10.6. RA faults
10.7. IR faults
10.8. IR disagree
10.9. IR alignment in ATT mode
10.10. FM/GPS position disagree

10.1. EGPWS alerts (memory item)

EGPWS alerts can be categorised into warnings and cautions. A warning is any alert with the instruction “Pull up” or “Avoid” attached. All other alerts are cautions. A warning may be downgraded to a caution if flying in daylight VMC and positive visual verification is made that no hazard exists, or if an applicable nuisance warning notice is promulgated in Company documentation [EOMA 8.3.6].

The response to a “Pull up” type warning is to call “Pull up, TOGA”, disconnect the autopilot and simultaneously roll the wings level, apply full backstick and set TOGA power. The speedbrake should then be checked retracted. Once the flight path is safe and the warning stops, accelerate and clean up as required. Note that it is highly likely that the autothrust ALPHA FLOOR protection will have engaged and thus the autothrust will need to be disengaged to cancel TOGA LK mode.

An “Avoid” warning indicates that a vertical manoeuvre alone is insufficient to prevent collision, and lateral avoiding action must also be taken. The response is essentially the same except that instead of rolling wings level, a turn must be initiated. The direction of the turn is at the discretion of the pilot, with the terrain or obstacle that is the source of the warning being displayed in red and black crosshatch on the ND.

The response to a caution is to correct the flight path or aircraft configuration as necessary. A configuration warning will almost always require a go around.

[FCOM PRO.AEP.SURV]

10.2. TCAS warnings (memory item)

TCAS warnings may be either traffic advisories (“Traffic, Traffic”) or resolution advisories (anything else).

From 28th January 2017, new easyJet deliveries are fitted with the new AP/FD TCAS mode. When this mode is fitted, the autopilot is capable of autonomously flying the TCAS escape manoeuvre. PF simply calls “TCAS blue, I have control” to establish who will take over if the autopilot does not respond appropriately, then calls the FMAs and monitors the autopilot as it flies the manoeuvre. If flying manually with flight directors and autothrust on, the flight directors will give standard guidance to fly the manoeuvre. If flying fully manually, the flight directors will pop up and the autothrust will engage, although it may be necessary to set the thrust levers to the climb gate.

If AP/FD TCAS mode is not installed or not available, the first response to either advisory is to call “TCAS, I have control” to unequivocally establish who will be carrying out any manoeuvres. If it is a resolution advisory, the autopilot should be disconnected and both flight directors turned off[33]. The autothrust remains engaged and reverts to speed mode. A vertical manoeuvre should then be flown to keep the V/S needle out of the red areas shown on the V/S scale. ATC should then be notified (e.g “Radar, Easy 123 – TCAS RA”). When clear of conflict, return to assigned level and re-engage the automatics (ATC phraseology: “Radar, Easy 123 – clear of conflict, returning to FL XXX”).

If a climb resolution advisory occurs on final approach, a go around must be flown.

[FCOM PRO.AEP.SURV, CAP413 1.7]

10.3. RNAV downgrades

RNAV operations fall into three main categories:

  1. RNAV approach (usually RNP 0.3)

  2. RNP-1 (aka PRNAV)

  3. RNP-5 (aka BRNAV)

The equipment that must be serviceable is listed in EOMB 2.3.18.3.2 for RNAV approach and FCOM PRO.SPO.51 for RNP SID/STAR.

The following messages indicate loss of RNAV capability:

  • NAV ACCUR DOWNGRAD (MCDU and ND) on both sides[34]

  • FMS1/FMS2 POS DIFF (MCDU)

  • NAV FM/GPS POS DISAGREE (ECAM)

  • CHECK IRS 1(2)(3)/FM POSITION (MCDU)[35]

For RNAV approaches, a go-around is mandated for any of these messages or if GPS PRIMARY LOST is annunciated on both NDs[36].

In an RNP-1 (PRNAV) environment, an RNAV downgrade may leave the aircraft unsure of position and below MSA. The initial response is to notify ATC with the phrase “Unable RNAV due equipment” and request reclearance. An immediate climb above MSA should be considered if a suitable alternative navigation method (e.g. radar vectors) is not available.

Some RNP-1 procedures specify additional downgrade criteria such as a requirement for dual RNAV systems or GPS. If GPS is not specifically mandated as an additional restriction, an RNP-1 procedure may still be flown without GPS PRIMARY: set RNP to 1, check NAV ACCURACY is HIGH and carry out a raw data check prior to commencement (see Section 10.10, “FM/GPS position disagree”).

Downgrades in an RNP-5 (BRNAV) environment are less critical as the aircraft will be above MSA. The IRSs provides RNP-5 required accuracy for two hours from last full alignment regardless of MCDU ENP, and it is acceptable to carry out a raw data check (see EOMB 2.3.15) to confirm that RNP-5 capability is maintained. If loss of RNP-5 capability is confirmed, inform ATC and continue with conventional navigation.

[FCOM PRO.SPO.51, EOM A.8.3.3.5, EOMB 2.3.18.3]

10.4. ADR faults

A single ADR fault simply requires switching to the hot spare and turning the affected unit off. Loss of ADR1 will lead to the loss of the extended functions of the EGPWS. Loss of ADR2 will lead to both baro reference channels being driven by the same FCU channel , so the baro refs should be checked.

Loss of two ADRs will lead to Alternate Law with associated speed restrictions and landing configuration considerations. Air data switching is used as necessary, and the affected ADRs are turned off. ATC switching may be required to restore transponder. If ADR 1 and 3 are lost, the landing gear safety valve is controlled closed, so the gear must be gravity extended and cannot subsequently be retracted. This is not mentioned by the ECAM – the gear will simply fail to extend normally.

If all three ADRs are lost, the result is airframe dependent. Some of the fleet now have a NAV ADR 1+2+3 FAULT ECAM and an appropriate procedure utilising the Backup Speed Scale, completing with the QRH AEP.NAV ALL ADR OFF paper procedure. For older airframes the ECAM displayed will be for Dual ADR failure and must be ignored since it will request meaningless air data and ATC switching. Instead revert to standby instruments (the standby ASI and Altimeter have direct pressure feeds from the the standby pitot and static ports) and refer to QRH AEP.NAV ADR 1+2+3 FAULT. Interestingly, when Backup Speed Scale is available, the ECAM advises that the standby instrument indications may be unreliable…

Triple ADR failure has a few additional ramifications. Of note is loss of automatic cabin pressure control (see Section 3.14, “Pressure controller faults” for manual pressure control methodology), Alternate Law and gravity gear extension. Of lesser concern are loss of stall warning, rudder travel limiter frozen until slat extension and loss of auto flap retraction.

[NAV ADR 1(2)(3)(1+2)(1+3)(2+3) FAULT, QRH AEP.NAV, FCOM PRO.AEP.NAV]

10.5. ADR disagree

The ECAM message indicates that, following an ADR fault or rejection, there is a speed or angle of attack disagreement between the two remaining ADRs. This will cause a degradation to alternate law. If there is a speed disagreement, see Section 2.3, “Unreliable airspeed (memory item). If the speed does not disagree, an AOA sensor is providing incorrect data and there is a risk of spurious stall warnings.

[NAV ADR DISAGREE, FCOM PRO.AEP.NAV]

10.6. RA faults

A single RA fault results in degradation of approach capability to Cat II.

Loss of both RAs will lead to Direct Law at landing gear extension and a loss of ILS APPR mode capability. Therefore, landing will be CONF 3 with associated corrections and the approach should be flown in LOC and FPA. The FCTM recommends that the final stages of the approach are flown raw data as the autopilot gains are not being updated and autopilot performance is likely to be unsatisfactory. Height callouts are not available.

[NAV RA 1(2) FAULT, FCOM PRO.AEP.NAV, FCTM AEP.NAV]

10.7. IR faults

In case of simultaneous loss of the ADR and IR associated with an ADIRU, apply the ADR FAULT procedure first.

A single IR fault will simply require ATT/HDG switching. This may lead to loss of the extended functions of the EGPWS and/or loss of TCAS. It may be possible to recover the IR in ATT mode (see Section 10.9, “IR alignment in ATT mode”).

A dual IR fault will lead to loss of PFD indications on at least one side so use ATT/HDG switching to recover. It will also lead to Alternate Law and associated speed restrictions and landing configuration considerations.

[NAV IR 1(2)(3)(1+2)(1+3)(2+3) FAULT, FCOM PRO.AEP.NAV]

10.8. IR disagree

Following rejection or failure of an IR, there is disagreement between the two remaining IRs. Normal and alternate laws are lost, but alternate law with reduced protections can be recovered by isolating the faulty IR (use standby horizon to cross-check) and resetting the ELACs.

[NAV IR DISAGREE, FCOM PRO.AEP.NAV]

10.9. IR alignment in ATT mode

If IR alignment is lost, it may be possible to recover attitude and heading information by switching the ADIRU selector to ATT and maintaining level constant speed flight for 30 seconds. The magnetic heading will need to be entered, the exact method being dependent on the ADIRS CDU fitted.

[IR Alignment IN ATT Mode, QRH AEP.NAV, FCOM PRO.AEP.NAV]

10.10. FM/GPS position disagree

This can be disregarded if on an ILS or LOC approach. On an overlay approach, revert to raw data. On an RNAV approach, go around unless visual.

In other flight phases, manually tune a VOR and check against either the needle and DME on the ND or the BRG/DIST TO field on the PROG page. If the error is greater than 3nm in the cruise or greater than 1nm for approach, raw data navigation and AP/FD selected lateral and vertical modes should be used.

[NAV FM/GPS POS DISAGREE, QRH AEP.NAV, FCOM PRO.AEP.NAV]



[33] If one FD is left engaged, the autothrust will not revert to speed mode, possibly resulting in speed decay and engagement of normal law protections.

[34] If NAV ACCUR DOWNGRAD occurs on one side only, the procedure may be continued using the unaffected FMGC.

[35] This is missing from the RNP-1 list in EOMB but is listed in the FCOM. It is not listed as a go around criteria for RNAV approach, but continuing would seem somewhat brave…

[36] If GPS PRIMARY LOST is annunciated on only one ND, the approach may be continued using the unaffected FMGC. There is also conflict between EOMA and EOMB as to whether GPS PRIMARY is required at all for RNAV(VOR/DME) or RNAV(DME/DME) etc. – I’ve gone with the most restrictive here.