Wing Anti-Ice

Wing anti-ice (WAI) is the bleed system's first big customer in ATA-30: it pipes 200 °C air into the leading edges of the four outboard slats of each wing so that supercooled water never gets a grip. Everything about its character — where the air comes from, what pressure it holds, what happens when it leaks, which way the valves fail — follows from that one fact: this is pneumatic ice protection. This article covers the system; its failure catalogue lives in article 12, its use through the flight in article 10, and its dispatch story in article 13. The pneumatic supply chain behind it is the ATA-36 series.

1. What it protects — and why only the outboard slats

Per FCOM DSC-30-20-10:

Hot air from the pneumatic system heats the four outboard slats (4-5-6-7) of each wing in flight.

Note both restrictions in one sentence: only slats 4 to 7, and only in flight (the ground behaviour is a 30-second test, §5). Why not the whole leading edge? Ice does not damage lift evenly along the span. The outboard wing has a shorter chord and a smaller leading-edge radius — a fine edge collects supercooled droplets far more efficiently than a blunt one — and the outboard sections sit ahead of the ailerons, where asymmetric stall becomes a roll problem. The inboard leading edge is blunter and partly shadowed by the engine nacelles. Bleed air is a finite budget, so it is spent where ice bites hardest. The unprotected remainder is not forgotten: the icing minimum-speed table in article 10 explicitly carries an allowance for ice accretion on non-heated structure.

Each wing is plumbed as two sub-systems. Per AMM 30-11-00:

The LH(RH) outer anti-ice valve controls the supply of the engine bleed air to the No 5, 6 and 7 slats. The LH(RH) inner anti-ice valve controls the supply of the engine bleed air to the No 4 slat.

Four valves in total — inner and outer per side — which is exactly why the ECAM alert titles in article 12 read L(R) INR(OUTR): the alert is naming one of these four. One switch commands them all:

The WING pushbutton on the ANTI ICE panel controls the four valves.

2. Where the air comes from: own engine first, crossbleed as backup

Per AMM 30-11-00:

The usual operation is to get its bleed-air supply from the engine on the same wing. If this bleed-air supply is not available, it is supplied from the engine on the other wing through a crossbleed valve.

That single sentence wires WAI into the ATA-36 distribution network. Lose one engine's bleed and the crossbleed valve can keep both wings protected — which is why the crossbleed fault procedure lists "WING ANTI-ICE on with one bleed inoperative" among the reasons to select the valve open manually (article 12). Lose both engine bleeds and there is nothing left to regulate: the dual-bleed-failure paperwork simply declares WING A.ICE NOT AVAILABLE and tells you to avoid icing conditions.

[!warning]- APU air can feed the packs — it must not feed the wings Per FCOM PRO-NOR-SOP (before takeoff): Use of the APU bleed is not permitted, if wing anti-ice is to be used. The abnormal procedures repeat it in stronger form (the APU BLEED pushbutton must not be used for wing anti-ice purpose). APU air is scheduled for air conditioning and engine starting; in the wing anti-ice ducts it cannot promise the pressure — or, critically, the temperature — that de-icing the slats requires (see the 150 °C line in §6). A memory hook: APU air is house air, not battle air.

3. The valve: regulator, shutoff and hand-lockable — in one butterfly

The wing anti-ice control valve is electrically controlled and pneumatically operated. The construction details (a three-chamber actuator, a pilot-valve needle feedback) are maintenance territory; what a pilot should carry are its three pressures. Per AMM 30-11-00:

The anti-ice valve controls its outlet pressure at 22.5 psi (1.5513 bar) plus or minus 2.5 psi (0.1724 bar). If the pressure increases to 31 psi (2.1374 bar) plus or minus 1 psi (0.0689 bar) (or decreases to 14 psi (0.9653 bar) plus or minus 1 psi (0.0689 bar)) the related switch gives a 'high pressure' or 'low pressure' signal.

The failure direction is the wing side of the chapter's fail-safe contrast:

NOTE: If a failure of the electrical or air supply occurs, the butterfly valve always closes.

The FCOM's crew-level version: In the event of electrical power supply failure, the valves close. Spring-loaded closed, powered open — because the wing's design fear is uncontrolled heat: a valve stuck open on a stationary aircraft can bake a slat (article 01 planted this contrast; the engine valve in article 03 fails the other way).

Two more built-in provisions matter operationally. Ground dispatch has a mechanical back door — per AMM 30-00-00, If a failure of a valve occurs on the ground, it can be manually locked in the open or closed position (this permits the aircraft to fly) — which is precisely the maintenance action behind the two MEL items in article 13 (locked closed: that zone has no protection; locked open: that zone is heated whenever bleed flows). And a stuck-open valve cannot run away thermally:

An in-line restrictor is installed in the duct downstream of each anti-ice valve. If an anti-ice valve has a failure in the open position, the restrictor limits the flow of air to the slats.

That restrictor is the hardware reason the in-flight "valve stuck open" procedure can afford to shrug — protection on the failed side is continuously available and the flow is bounded (article 12).

4. Distribution: piccolo tubes and the art of even heating

Per AMM 30-11-00:

The piccolo tubes release the air into the slats through holes along their forward length. The air flows around the forward area of the slat then goes through acceleration slots into the rear section. It is then released overboard through the holes in the bottom surface of the slat.

So the air enters through a perforated spray-bar (the piccolo tube), washes the inside of the leading edge, accelerates through slots into the rear of the slat and exits through holes in the slat's lower surface. The tube diameters taper along the span — 80 mm in slat 4, 63.5 mm in slat 5, 58 mm in slat 6, and 58 mm narrowing to 38 mm across slat 7 (AMM component data). A piccolo tube is deliberately a leaking flute: keep the bore constant and the pressure — and therefore the jet strength — would sag hole by hole toward the tip. Necking the tube down keeps the last hole blowing as hard as the first. Even spanwise heating is the goal; the taper is the method. Because the slats move, the plumbing moves too: telescopic ducts (three concentric tubes) follow slat extension, and flexible ducts jump the air from slat 6 across to slats 5 and 7 — a layer of mechanism the fixed engine-intake system never needs.

5. Control logic: the 30 / 35 / 40-second ladder

The FCOM gives the ground rule; the AMM explains who enforces it and why. Per FCOM DSC-30-20-10:

When the aircraft is on ground, the flight crew can initiate a 30 s test sequence by turning the system ON.

Per AMM 30-11-00:

The system is only used during flight, but can be tested on the ground. To prevent heat damage to the slats, the ground test stops automatically after 30 seconds.

In flight, ram airflow carries the heat away — the slat is cooled as fast as it is warmed. Parked, the same 200 °C air just accumulates in aluminium. So the ground gets 30 seconds — enough to prove the valves open and pressure builds — enforced by a dedicated ground-test relay (The relay 4DL also limits the system operation time to 30 seconds to prevent the slats from overheating), with air/ground discrimination from the LGCIUs. Above that sit two more rungs:

If the test continues for more than 35 seconds, the ECAM shows the warning message ANTI-ICE GND TST OVRUN on the EWD. The crew must then stop the operation of the wing ice-protection system to prevent heat-damage to the slats.

And at 40 seconds with the valves still open, the A.ICE WING OPEN ON GND alert triggers (article 12). Read the ladder as designed escalation: 30 s — the timer should have closed it; 35 s — the display asks you to; 40 s — the system formally declares it will not close. Five-second margins between "automation acts", "human is prompted" and "alert is raised".

The FAULT light has a scripted false alarm worth pre-briefing:

Note: The amber FAULT light comes on briefly during pressure built up, or when the valves open.

Mechanically: at switch-on the valve is open but the duct has not yet pressurised, so the low-pressure switch still reads low and the FAULT circuit is live; once pressure climbs through 14 ± 1 psi the fault relay re-energises and the light goes out. The light's on-time is the duct's fill time — a light that stays on is the real event (LO PR follows). The ECAM adds its own de-bounce: failure-data transmission is suppressed for 10 seconds after switching the system on and 20 seconds after switching it off (AMM), so valve transients never page the crew.

6. The thrust bill and the temperature handcuff

Selecting WAI changes the engines' manners immediately. Per FCOM DSC-30-20-10:

When wing anti-ice is selected, the N1 or EPR limit is automatically reduced, and the idle N1 or EPR is automatically increased.

Both ends move for the same reason: air extracted ahead of the combustor is work the turbine never sees, so the rated-thrust ceiling drops; and the compressor must stay spooled high enough to feed the extraction, so idle rises. The operational costs land elsewhere in the series — a shallower idle-descent path needing half speedbrake (article 10) and a measurable fuel bill when a valve jams open (article 13).

Temperature is the quieter handcuff. The zone controller normally saves precooler effort by asking the bleed system to regulate down from 200 °C to 150 °C — but per FCOM DSC-21-10-30, This reduction is inhibited, if the wing-anti ice is ON. Because 150 °C is WAI's body-temperature floor: in flight, bleed air below 150 °C with the WING pushbutton on triggers the AIR BLEED LO TEMP alert, whose note states the air is too low for correct wing deicing and whose first remedy is to push the thrust up (article 12). One sentence to keep: WAI on locks the bleed at the 200 °C schedule; sagging below 150 °C is an alert and a thrust problem.

7. Leak self-protection and the ice-detection handshake

Per FCOM DSC-30-20-10:

If the system detects a leak during normal operation, the affected side's wing anti-ice valve automatically closes (Refer to DSC-36-10-60 Leak Detection).

The eutectic-salt loops, their 124 °C threshold and the "isolate the whole side" convention are ATA-36 material (leak detection); the ATA-30 consequence is simply that a WING LEAK confiscates that side's wing anti-ice along with its bleed. The other handshake goes to the ice detectors. Per AMM 30-11-00:

If the wing ice-protection system is set to off and ice is detected, the ECAM upper DU shows a warning message. This advises the crew to set the wing ice-protection system to ON.

Mind the verb — advises. The detection system recommends; the switch stays yours (article 06 builds the whole advisory philosophy on that verb).

8. Operating it: pushbutton, MEMO, BLEED page

Pushbutton states (FCOM DSC-30-20-20): off — ON light out, valves closed. FAULT (amber) — valve position disagrees with the commanded position, or low pressure is detected, with an ECAM caution. ON — blue light, WING A.ICE memo, and the conditional worth quoting:

Wing anti-ice control valves open, if pneumatic supply is available.

On the ground, they open for the 30-second test only — the SOP phrasing is explicit that after the self-test the valves close as long as the aircraft is on ground.

MEMO lines: WING A.ICE : This memo appears in green if the WING ANTI ICE pb-sw is ON. The companion advisory — ICE NOT DET appearing when no ice has been detected for 130 seconds after switch-on — and the pulsing "ice has gone" behaviour belong to the ice-detection story (article 06). Cockpit shorthand: steady memo = you selected it; pulsing memo = the detectors suggest you de-select it.

BLEED page: with the WING pushbutton on and both valves of a side open, the ANTI ICE legend shows white with green valve arrows; amber means at least one valve disagrees with the selection. The arrow's "open but amber" triad is a ready-made troubleshooting index — per FCOM DSC-36-20:

The valve is open, and at least one of the following conditions is met: ‐ Bleed air pressure high or low ‐ Wing anti-ice pb is at OFF position ‐ Open for more than 35 s, while the aircraft is on ground.

Three conditions mapping one-to-one onto three failure families: HI/LO PR, WING OPEN, and the ground-test overrun. One glance at the arrow colour tells you which page of article 12 you are about to need.

Self-test

[!note]- Q1. Which slats does WAI protect, and which valve feeds which?

Slats 4-5-6-7 of each wing. The inner valve of each side feeds slat 4; the outer valve feeds slats 5, 6 and 7. Four valves total — hence the L(R) INR(OUTR) naming in the ECAM alerts.

[!note]- Q2. Name the three pressures and explain the FAULT light's "brief flash" at switch-on.

Regulation 22.5 ± 2.5 psi; high-pressure switch 31 ± 1 psi; low-pressure switch 14 ± 1 psi. At switch-on the duct is still filling, so the low-pressure switch holds the FAULT light on until pressure rises through 14 ± 1 psi — the flash lasts exactly as long as the fill.

[!note]- Q3. Recite the 30/35/40-second ladder and the reason the ground only gets 30 seconds.

30 s — ground-test relay closes the valves automatically (no ram cooling on the ground; the slats would overheat). 35 s — ANTI-ICE GND TST OVRUN appears on the EWD, telling the crew to switch off. 40 s — A.ICE WING OPEN ON GND: the system declares the valves failed open.

[!note]- Q4. Why does the piccolo tube taper toward the wing tip, and where does the air finally go?

A perforated tube at constant bore loses pressure hole by hole; necking it down keeps the last hole blowing as hard as the first, for even spanwise heating. The spent air crosses the slat interior through acceleration slots and exits overboard through holes in the slat's lower surface.

[!note]- Q5. One engine's bleed is lost in icing. How does WAI survive — and why is APU air not the answer?

Open the crossbleed: the opposite engine feeds both wings. APU bleed is prohibited for wing anti-ice — it cannot guarantee the pressure and temperature the slats need (150 °C floor). House air, not battle air.

[!note]- Q6. What two things happen to engine parameters the moment WAI is selected, and what temperature handcuff comes with it?

The N1/EPR limit drops and idle N1/EPR rises. The bleed system is also held at the 200 °C schedule (the 150 °C economy setting is inhibited); if bleed temperature still sags below 150 °C in flight with WAI on, AIR BLEED LO TEMP triggers and the remedy starts with more thrust.

Key takeaways

References

Protected slats, single-pushbutton control, ground 30-second test, leak auto-closure, thrust-limit and idle changes, and electrical-failure closure per FCOM DSC-30-20-10; pushbutton states, FAULT transient note, pneumatic-supply conditional and MEMO lines per FCOM DSC-30-20-20. Same-side/crossbleed supply, inner/outer valve assignment, in-line restrictor, piccolo and telescopic-duct arrangement, valve regulation and switch values, fail-closed note, ground-test relay, ECAM transmission suppression windows and ground-test overrun message per AMM 30-11-00 (Description and Operation); manual valve locking per AMM 30-00-00. APU-bleed prohibition per FCOM normal procedures (before takeoff) and the air abnormal procedures. Zone-controller temperature-reduction inhibit per FCOM DSC-21-10-30; BLEED-page arrow conditions per FCOM DSC-36-20; the 150 °C low-temperature alert per the FCOM air abnormal procedures. The collection-efficiency rationale for outboard-only coverage, the "leaking flute" explanation of the taper and the escalation reading of the time ladder are integrative syntheses of the referenced material.

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.