Abnormals II — Wing & Engine Anti-Ice Failures

Hot-air ice protection fails into exactly two endgames: get the air back, or concede symmetrically and stay out of the ice. The wing family's eight alerts orbit four valves and one relay; the engine family is two alerts and done; ice detection adds three and the windshields three more. But the deep water is cross-chapter — bleed (ATA-36), electrics (ATA-24) and engine (ATA-70) failures can each take WING A.ICE out of your hands without a single ATA-30 alert firing. Systems background: wing, engine, detection; the probe family was article 11; the day-after dispatch story is article 13.

1. The failure tree at a glance

A WAI alert asks one question: what state is the air path in?
├─ Pressure wrong (valve regulating, badly)
│   ├─ HI PR (31 psi switch) ..... crew awareness — the chapter's quietest alert
│   └─ LO PR (14 psi switch) ..... THRUST: go find the pressure
│                                   └─ unsuccessful → OFF + avoid icing [+ severe-ice package]
├─ Valve disobeying
│   ├─ Won't open (VLVE NOT OPEN, flight) → OFF + avoid icing [package]  (asymmetry!)
│   ├─ Won't close (WING OPEN) → ground: cut all three air feeds
│   │                            flight: free anti-ice — keep using it
│   └─ Ground test overrun (WING OPEN ON GND, 40 s) → OFF; WAI AVAIL IN FLT
└─ Relay coup (WAI SYS FAULT — one relay commands all four valves)
    ├─ pb OFF, all valves open  → both-sides WING OPEN (ground isolate / flight usable)
    └─ pb ON, all valves closed → equivalent to total WAI loss → OFF + avoid icing [package]

[severe-ice package] = speed floor (G DOT clean / VLS+10 otherwise) + manoeuvre with care
                     + approach: FLAP LVR 3, APPR SPD VLS+10, landing-distance procedure

The engine side has no such tree — its valve is two-position, so the stories are "abnormally closed" (one line: avoid icing) and "abnormally open" (a fuel bill now, a thrust trap at the next takeoff). Everything else in this article is other chapters reaching in.

2. Wing family — pressure: push the levers before you surrender

Low pressure is the lead actor — the procedural face of article 02's 14 psi switch. Per the FCOM anti-ice abnormal procedures:

This alert triggers when a low pressure in the wing anti ice duct is detected and the WING ANTI ICE pb-sw is set to ON.

The first action line is thrust — increase it. The logic runs through ATA-36: WAI's upstream is engine bleed, and at low power the bleed ports simply deliver less (stage selection); the regulator holds 22.5 psi only if the supply above it is worth regulating. Spool up, port pressure rises, and duct pressure very often walks back in. Only if unsuccessful do you concede: WING ANTI ICE OFF, avoid icing conditions — and, when severe ice accretion is the backdrop, the family's shared package appears on STATUS. Its speed floor:

Note: The speed must not be lower than: ‐ G DOT, when in CONF 0 ‐ VLS + 10 kt, for other configurations.

That is article 10's speed table, "WAI failed" row. The approach lines complete the package — FLAP 3 for landing (one less high-drag configuration exposed to accretion), approach speed VLS + 10 kt, landing-distance procedure applied. And the package ends with a flight-quality note worth memorising whole:

Note: In the case of severe ice accretion, with wing anti ice failed, the angle-of-attack protections are still efficient. However, if full back stick is maintained while at maximum angle-of-attack, a divergent roll oscillation may appear. Releasing slightly the stick will stop this oscillation.

[!warning]- The protection holds; don't grind against it An iced wing stalls asymmetrically — held at maximum angle-of-attack, separation breaks out on one side first, and the mismatch feeds a divergent roll oscillation even with alpha protection fully serviceable. The protection keeps the wing flying; it does not make the iced wing symmetric. The cure is written in the note: release the stick slightly. Protections are a fence, not a bench — with ice on the wing, don't lean on them.

High pressure (the 31 psi switch) is the chapter's lowest-key alert: crew awareness only — no FAULT light, no aural, just the ECAM line and the BLEED page. The regulator has failed toward the high side, and the restrictor downstream is the mechanical backstop (article 02). Watch, and carry on.

3. Wing family — stuck open: enemy on the ground, gift in the air

Per the FCOM anti-ice abnormal procedures, the ground version:

This alert triggers on ground when one wing anti ice valve remains open and the WING ANTI ICE pb-sw is set to OFF.

The ground response is a siege — cut every feed the stuck valve could eat from: WING ANTI ICE OFF, crossbleed CLOSE, the affected side's ENG BLEED OFF, and APU BLEED OFF if the left wing is affected (the APU delivers into the left side of the manifold — ATA-36 topology — so it only matters when the leak of heat is on its side of the closed crossbleed). After takeoff, above 1500 ft, the recall hands everything back: ENG BLEED ON, X BLEED AUTO, WING ANTI ICE as required — because the airborne verdict is entirely different:

On the failed side, wing anti-ice is continually ON, and is therefore available, if needed.

[!warning]- Same failure, opposite verdicts — the environment decides On the ground, an open valve means continuous 200 °C heating of a slat that the 30-second test window exists to protect (article 02) — structural damage, so starve it. In flight, ram airflow carries the heat away and the same stuck valve becomes free anti-ice: the failed side is permanently protected, at the price of bleed consumption (the crossbleed is managed OPEN or AUTO to keep it fed; STATUS books the engine-bleed and pack consequences). Land, and the recall flips the page back to "enemy" — the ground isolation drill reappears. It is not a new failure; it is the same valve meeting a different environment.

The mild cousin is the ground test overrun:

This alert triggers when the aircraft is on ground and the wing anti ice valves remain open for more than 40 s after the WING ANTI ICE pb-sw is set to ON.

Thirty seconds is the test; at forty the system declares the auto-close missed (article 02's 30/35/40 ladder). Response: WING ANTI ICE OFF — and STATUS posts WAI AVAIL IN FLT. No more ground games; the airborne system is untouched.

4. Wing family — the relay coup and the symmetry rule

Per the FCOM anti-ice abnormal procedures:

This alert triggers when the when the wing anti-ice relay is failed.

(The doubled when the is the source text's own.) One relay carries the command to all four valves (article 02) — when it defects, the fleet of valves goes with it, so the alert has two faces. Pushbutton OFF with all valves open is a both-sides WING OPEN: on the ground the siege widens to all engine bleeds plus APU plus crossbleed; in flight (or through the 1500 ft recall) supply is restored and the MEMO typically shows WING ANTI ICE ON — both wings on free anti-ice, with ENG BLEED (ALL) booked inoperative for management. Pushbutton ON with all valves closed is the other face: functionally a total WAI loss — OFF, avoid icing, severe-ice package.

The single-valve "won't open" completes the family:

This alert triggers in flight when one wing anti ice remains closed and the WING ANTI ICE pb-sw is set to ON.

Response: the same full concession — OFF, avoid icing, package.

[!warning]- One valve fails to open; all four get switched off Three good valves remain — and the procedure shuts them anyway, because asymmetric anti-ice is more dangerous than none. One wing with clean slats and one wing carrying ice means two different stall characters on the two sides of the centreline — the roll-oscillation note of §2 as a pre-existing condition. WAI's failure philosophy in one line: better symmetrically without than asymmetrically with.

5. Engine family — two positions, two stories

Abnormally closed. Per the FCOM anti-ice abnormal procedures:

This alert triggers when the valve is abnormally closed.

The procedure is a single line — avoid icing conditions — with no "try thrust first". The engine anti-ice valve is two-position (article 03): there is no regulation midpoint for pressure to recover into, and since loss of electrical supply drives the valve open, a valve stuck closed is almost certainly mechanical. Airborne, that has no fix.

Abnormally open doesn't even earn a procedure — crew awareness — but the second-level text buries a takeoff mine:

If the fault occurs before takeoff, it may cause an ENG THRUST LOSS caution during takeoff power application.

The mechanism is article 03's accounting: a stuck-open valve bleeds the HP compressor continuously while the FADEC's thrust datum still believes anti-ice is off — actual thrust sits below the datum, and applying takeoff power exposes the gap. The disarm lives in dispatch: the FCOM points to the MMEL item for an open engine anti-ice valve, and the dispatch procedure has you select that engine's pushbutton ON — command aligned with reality, FADEC computing on the "anti-ice on" datum, mine removed (article 13). The same family logic appears in the takeoff-thrust-disagree alert: if the disagreement traces to abnormal engine or wing anti-ice configuration, the branch is THR LEVERS IDLE — takeoff abandoned until the anti-ice configuration is straightened out.

One more engine-side alert is really a visibility failure. Per the FCOM engine abnormal procedures:

This alert triggers when either bleed valves, pack valves, wing and engine anti-ice valves or crossbleed valve position status is not received by the active FADEC channel.

A FADEC that cannot see valve positions cannot trim its thrust datum. The before-takeoff counter is to push the configuration to a known, most-conservative state — packs off, affected engine anti-ice ON, wing anti-ice ON: everything open, datum computed for everything open, no more guessing.

6. The detection family and SEVERE ICE DETECTED

Loss of both detectors (article 06's grading):

This alert triggers when the ice detection system is lost.

Procedure: ANTI ICE — as required. The crew inherits the detectors' job with article 01's definition and their own eyes (the dispatch version of that discipline is in article 13). ICE DETECTED is likewise a single line — ENG (ALL) ANTI ICE ON. SEVERE ICE DETECTED is the family at full dress: engines ON, then ignition —

This line is displayed, if continuous IGNITION is not automatically selected.

(Severe ice sheds in slabs, and slabs go through engines: continuous ignition is flameout insurance — the manual echo of article 03's automatic EIU selection.) Then the wing branch splits on the bleed system's health: if the bleed configuration permits, WING ANTI ICE ON; if a bleed failure forbids it, WING ANTI ICE OFF and avoid icing conditions — severe ice stacked on a limping bleed system has one exit, and it is the nearest door out of the icing area (§7).

The windshield trio closes the ATA-30 list: a windshield-heat failure's procedure line — if due to a WHC command failure, PROBE/WINDOW HEAT ON — is article 05's pushbutton bypassing the WHC automatics; side-window heat alerts are crew awareness (demisting only). The arcing scenario and the ground overheat false alert are handled in article 05.

7. Cross-chapter I — four ways the bleed system takes WAI away

Air arrives, but not hot enough. Per the FCOM air abnormal procedures:

This alert triggers when the engine bleed supplies bleed air at a temperature below 150 °C in flight and the WING A-ICE pb-sw is set to ON.

In flight, engine bleed temperature is too low for correct wing deicing.

The 150 °C line is article 02's floor made procedural, and the first response is the same reflex as LO PR — thrust — with one operating detail attached:

The thrust lever of the affected engine must be advanced with the autothrust OFF.

(Leave autothrust engaged and it politely pulls back whatever you push forward.) Idle bleed is both soft and cold — pressure and temperature ride the same spool. If thrust doesn't cure it: one side affected → that side's ENG BLEED OFF and let the crossbleed deliver the other engine's hot air; both sides → WING ANTI ICE OFF, avoid icing, package.

The abnormal-bleed-configuration family touches WAI twice. An overheating bleed with a stuck valve ends in PACK OFF, WING A.ICE OFF, avoid icing. And one iron law rides along:

Note: APU BLEED pb-sw must not be used for wing anti-ice purpose, or after ENG 1 FIRE.

The first half is article 02's SOP prohibition in abnormal dress (unregulated APU air against a fixed orifice); the second half is fire isolation — the APU line enters the left side, and after an engine 1 fire that side accepts no air from anyone.

The precooler makes WAI a suspect. Per the FCOM air abnormal procedures:

This alert triggers when the precooler outlet temperature is above 240 °C and when: ‐ The wing anti-ice is activated above FL 320, or ‐ The PACK FLOW selector is not in the LO position, or ‐ The cargo COOLING selector is in the MAX position.

High and thin, fan air is a weak coolant — and WAI holds the bleed at its 200 °C setpoint. If the alert persists, the procedure takes wing anti-ice away (OFF, avoid icing). Running WAI for long stretches above FL 320 is itself a cue to keep half an eye on bleed temperature.

The crossbleed's manual position lists WAI third among its reasons to exist. Per the FCOM air abnormal procedures:

Select OPEN, when the APU BLEED pb-sw is ON, or for engine start, or when WING ANTI-ICE pb-sw is ON with one bleed inoperative.

And the endgame is the dual bleed failure: every branch of that QRH procedure carries the line WING A.ICE NOT AVAILABLE, a ceiling (FL 220 with APU bleed supplying; FL 100 or minimum safe altitude without), and AVOID ICING CONDITIONS. An aircraft with no air answers every anti-ice question the same way: don't be where the ice is.

8. Cross-chapter II — anti-ice buttons inside engine procedures

Engine stall (parameters-normal branch): affected engine's anti-ice ON, wing anti-ice ON. The second-level text explains:

Operation of the engine and wing anti-ice will increase the stall margin but EGT will increase accordingly.

Drawing more bleed lowers the compressor's back-pressure and unchokes the flow; the bill goes to the turbine as heat. The anti-ice buttons here are bleed-demand knobs — nothing to do with ice at all.

High N1 vibration starts with a diagnosis. Per the FCOM engine abnormal procedures:

An increase of the N1 vibrations in icing conditions, with or without engine anti-ice, may be due to icing of the fan blades and/or spinner. Ice accretion on the engine fan may result in a temporary increase of the EGT.

With or without engine anti-ice — because EAI heats the intake lip only (article 03); the fan is its lawful blind spot. The FCTM compresses suspicion into one sentence:

The flight crew should suspect icing if N1 vibrations occur without variation on other engine parameters.

Suspected, the QRH's airborne shedding drill is the in-flight sibling of article 09's ground run-ups: autothrust off, thrust (one engine at a time) idle then increase toward high N1 —

If ENG ANTI ICE is off, switch it ON at idle fan speed, one engine after the other with approximately 30 s interval. To shed ice, it may be necessary to perform several thrust variations between idle and a thrust compatible with the flight phase.

Switch it on at idle — don't time the valve's thermal shock to a spinning-fast fan; one engine after the other — never have both engines shaking ice loose at once.

Relight and all-engine-failure procedures cast WAI only to switch it off: before a starter-assisted relight the bleed must serve the starter, not the slats — and the all-engine-failure drill pairs its WING ANTI ICE OFF lines with the note:

Green dot speed is the optimum speed for starter-assisted relight with the APU bleed.

Engine fire: the affected side's wing anti-ice goes OFF as part of a total quarantine — per the FCOM, The affected side is isolated from any source of air. Volcanic ash inverts the family one last time: engine and wing anti-ice ON — the heated airflow doubles as a purge for ash-choked surfaces — with the counter-clause that before any relight attempt, wing anti-ice goes back OFF to give the starter its air.

9. Cross-chapter III — the electrical network decides what survives

The emergency-electrical remaining-systems table answers ICE & RAIN in four columns (emergency generator running / batteries only / engine-pump hydraulics / RAT). The load-bearing rows, per the FCOM electrical abnormal procedures:

WING A.ICE Norm Inop Inop Inop ENG A.ICE Open Open Open Open CAPT PITOT Norm Norm Norm Norm

Read it slowly: WING A.ICE is Norm only with the emergency generator — everywhere below that, gone. ENG A.ICE is Open in all four states — the fail-open valve (article 03) turns total electrical poverty into permanent, unregulated, working engine anti-ice, at the standing fuel cost of a stuck-open valve. The captain's pitot survives everything — article 01's emergency trio in table form (captain and standby probes), with window heat 1 recovering only under the emergency generator (and not while the RAT alone is driving it), and rain repellent remaining on the captain's side in all four columns.

Single DC-bus failures read like a seating plan of article 01's power map: DC BUS 1 takes the captain's wiper; DC BUS 2 takes the first officer's static and TAT heating, the right windshield and window heat, the first officer's wiper and rain repellent; both together add up to no wipers at all and a CAT 2 ceiling; and DC ESS — the essential bus — takes wing anti-ice itself, the left windshield and window, the captain's AOA and rain repellent, and posts AVOID ICING CONDITIONS with the severe-ice package straight onto STATUS. The teaching habit: on any major electrical failure, go read the ICE & RAIN section of STATUS first — ice protection's fate is a fixed by-product of the power distribution.

10. The four endgames, distilled

"Avoid icing conditions" is not a benediction. Executed, it means article 01's definition run backwards — change level or routing to leave the overlap of visible moisture and near-freezing temperature; if already inside, the task is out, promptly, and until out, the package speeds are your floor. And both middle rows of the table end at the same desk: logbook entry, then article 13 for tomorrow's dispatch — remembering that a WING OPEN carried through flight will re-present its ground isolation drill at landing via the recall. Same valve, old news.

Self-test

[!note]- Q1. WING LO PR — first recovery action, its mechanism, and the concession if it fails?

Thrust increase: WAI drinks from engine bleed, and idle-power ports deliver little for the 22.5 psi regulator to work with — spool up and duct pressure usually returns. Unsuccessful: WING ANTI ICE OFF, avoid icing conditions, and in severe accretion the package — G DOT/VLS+10 floors, careful manoeuvre, FLAP 3 landing with VLS+10 and the landing-distance procedure.

[!note]- Q2. The roll-oscillation note: are protections still working? What provokes the oscillation, and what stops it?

Protections remain efficient. Holding full back stick at maximum angle-of-attack on an iced wing lets asymmetric separation feed a divergent roll oscillation; releasing the stick slightly stops it. The fence holds — don't grind against it.

[!note]- Q3. Why are the ground and flight versions of WING OPEN opposite — and why does APU BLEED go off only for a left-wing case?

Ground: continuous heating threatens the slat structure, so every feed is cut — engine bleed, crossbleed, APU. Flight: ram air carries the heat away and the stuck valve is free anti-ice, kept fed and used as needed. The APU enters the manifold on the left; with the crossbleed closed it can only feed a left-wing valve, so only then does switching it off starve anything.

[!note]- Q4. One wing valve won't open. Three are healthy. Why shut all four?

Asymmetric anti-ice gives the two wings two different stall characters — the pre-condition of the roll-oscillation note. Better symmetrically without than asymmetrically with; hence OFF, avoid icing, package.

[!note]- Q5. What mine does a stuck-open engine valve plant for takeoff, and how does dispatch defuse it?

An ENG THRUST LOSS caution at takeoff power: the valve bleeds the HP compressor while the FADEC datum assumes anti-ice off. The dispatch procedure selects that engine's anti-ice pushbutton ON — command matches reality, the datum includes the bleed, no disagreement left to alert on.

[!note]- Q6. SEVERE ICE DETECTED — the full sequence and the wing branch's two exits?

Engines ON; ignition selected if continuous ignition hasn't self-selected (slab shedding = flameout insurance); then wing anti-ice ON if the bleed configuration permits — or OFF plus avoid icing conditions if a bleed failure forbids it, which is the severe-ice-on-a-limping-bleed case whose only move is leaving the icing area.

[!note]- Q7. Emergency electrical configuration: state of WING A.ICE, ENG A.ICE, the captain's pitot — and what does STATUS post when DC ESS alone is lost?

WING A.ICE Norm only with the emergency generator, otherwise Inop; ENG A.ICE Open in all four states (fail-open valve = unregulated but working); captain's pitot Norm throughout. DC ESS loss takes wing anti-ice, left windshield/window, captain's AOA and rain repellent — and posts AVOID ICING CONDITIONS with the package.

Key takeaways

References

Wing-family triggers (low/high pressure, open on ground/in flight, 40 s ground overrun, relay fault, valve not open), the continually-ON note, speed-floor and roll-oscillation notes, approach package lines, engine valve closed/open with the ENG THRUST LOSS second-level note and MMEL pointer, ice-detection and SEVERE ICE procedures with the ignition display condition, and windshield-heat lines per the FCOM anti-ice and severe-ice abnormal procedures. Bleed-side material — the 150 °C low-temperature alert with its autothrust note, the APU-bleed prohibition, the precooler condition set, and the crossbleed manual-OPEN cases — per the FCOM air abnormal procedures; the dual-bleed endgame (wing anti-ice unavailable, ceilings, avoid icing) per the QRH. Engine-side quotes (stall margin, fan-blade icing and EGT, position-status alert, green-dot relight note, fire-side air isolation) per the FCOM engine abnormal procedures; the one-sentence suspicion criterion per the FCTM; the airborne shedding drill per the QRH. The remaining-systems rows per the FCOM electrical abnormal procedures. The failure tree, the four-endgames table, the DC-bus consequence lists and the ground-versus-flight framing are integrative syntheses of the referenced material; takeoff-thrust-disagree and volcanic-ash lines are condensed from the corresponding FCOM/QRH procedures.

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.