Ice and Rain Protection — System Overview and Icing Conditions

Ice attacks more of the aircraft at once than almost any other threat: it reshapes the wing, chokes the engine intakes, lies to the air-data probes, blinds the windshield, bursts water lines and can even freeze the escape-slide locks shut. ATA-30 is therefore not one system but a defence map organised by body part — hot air for two large surfaces, electric heat for everything small and scattered, a pair of "eyes" (the ice detection system) and a rain kit for the windshield. This opening article lays out that map and plants the chapter's legal foundations: the definitions of icing conditions, severe ice accretion and thin hoarfrost that every later decision hangs on. Wing anti-ice follows in article 02, engine anti-ice in article 03, probe heat in article 04, windows and rain removal in article 05, ice detection in article 06, the water and door-slide systems in article 07, then three operations articles (08, 09, 10), the failure catalogue (11, 12) and dispatch (13).

1. The mission in one word: unrestricted

Per FCOM DSC-30-10-10:

The ice and rain protection system allows unrestricted operation of the aircraft in icing conditions and heavy rain.

The AMM says the same thing in maintenance language — the system lets the aircraft operate, without restrictions, in conditions of ice or heavy rain. "Unrestricted" is the acceptance standard for the whole chapter: with this equipment serviceable, dispatch does not stop because icing conditions exist along the route. Keep the converse in mind, because it shapes everything in article 13: the moment a protection item is inoperative, the dispatch conditions almost always bolt on a weather fence — no flight in known or forecast icing conditions.

2. Two weapons: hot air and electric heat

Per FCOM DSC-30-10-10:

Either hot air or electrical heating protects critical areas of the aircraft as follows:

The FCOM's split is simple. Hot air protects the four outboard leading-edge slats of each wing and the engine air intakes. Electric heat protects the flight-compartment windows, the sensors (pitot probes, static ports, TAT probes, angle-of-attack probes) and the waste-water drain mast. Rain removal is mechanical and chemical: wipers on each front windshield, plus a rain-repellent fluid system.

Why this division of labour? Anti-icing a surface means feeding it heat continuously over area. The slat leading edges and the intake lips are large curved surfaces — electric elements sized for that job would be prohibitively heavy, while 200 °C bleed air is available on tap from the pneumatic system (see the ATA-36 series). Probes, window panes and drain lines are small or far from any duct run, so copper wins there. A memory hook that survives the simulator: big surfaces breathe air, small parts run on wire.

The AMM's census is longer than the FCOM's, and the difference is worth teaching. Per AMM 30-00-00:

The electrically heated areas/systems are: - the cockpit windshield (for ice protection) - the cockpit windows (for defogging) - the Angle Of Attack (AOA) sensors - the Total Air Temperature (TAT) sensors - the Pitot and Static probes of the Air Data/Inertial Reference System (ADIRS) - the escape slide locking mechanism - the waste water system - the water servicing panel - the potable water system.

[!warning]- The AMM map has eleven tiles; the FCOM draws only eight Three systems appear in the AMM list that the FCOM never mentions: the escape-slide locking-mechanism ice protection, the water servicing-panel heating and the potable-water ice protection. All three are fully automatic, have no cockpit control and raise no ECAM alert — and the FCOM is a pilot's operating manual, so anything a pilot cannot operate simply is not in it. You should still know they exist (article 07): cabin crew can see a WATER ICE PROTECTION status page, and the MEL has a waste-water heating item. Note also the precision in the window line: the windshield gets ice protection, the side windows only defogging — the side panes carry no anti-ice duty (article 05).

One more AMM sentence anchors the chapter's supply lines:

The engine bleed air system supplies the hot air. The AC BUS, DC BUS, and DC ESS BUS supply the electrical power.

Ice protection generates nothing itself — it is a customer of the bleed network (ATA-36) and the electrical network (ATA-24). Every cross-chapter failure in article 12 is, at root, a supply cut.

3. The chapter's first pillar: what "icing conditions" means

The Limitations chapter gives the definition that every anti-ice decision in this aircraft references. Both sentences matter. Per FCOM LIM (Ice and Rain Protection):

Icing conditions exist when the OAT (on ground or after takeoff) or the TAT (in flight) is at or below 10 °C and visible moisture in any form is present (such as clouds, fog with visibility of 1 sm (1 600 m) or less, rain, snow, sleet or ice crystals).

Icing conditions also exist when the OAT on the ground and for takeoff is at or below 10 °C and operating on ramps, taxiways or runways where surface snow, standing water or slush may be ingested by the engines, or freeze on engines, nacelles or engine sensor probes.

Read them as "one cold, two waters":

[!warning]- Why 10 °C when water freezes at 0 °C? Two effects eat the margin. Local flow acceleration around a leading edge or an intake lip drops static pressure and static temperature well below the free-stream value, and supercooled droplets evaporating on impact absorb further heat. The 10 °C figure builds those local effects into the definition, so the crew never has to estimate them. The exam trap runs the other way: quoting "below zero" as the icing threshold is wrong by ten degrees.

Why OAT on the ground but TAT in flight? Stationary, the two are essentially equal. In flight, ram rise means the skin and probes feel total temperature — so TAT is the number the hardware experiences. Hold that thought for article 10: ice crystals can freeze the TAT probe itself, pinning the indication near 0 °C and quietly corrupting this very criterion.

This 10 °C is the first rung of a temperature ladder that the rest of the series climbs — four numbers, four different jobs:

4. Pillars two and three: severe ice, thin hoarfrost

Per FCOM LIM:

Ice accretion is considered severe when the ice accumulation on the airframe reaches approximately 5 mm (0.2 in) thick or more.

That 5 mm is the most elegant closed loop in the chapter. The limitations chapter defines it; the ice detectors are calibrated so that their SEVERITY signal — seven elementary detections — corresponds to approximately 5 mm on the wing tips (article 06); and the abnormal procedures translate it into a speed-and-configuration package (minimum speed VLS +10 kt / green dot, FLAP 3 landing — article 12). One number stitches definition, sensor and procedure together.

Thin hoarfrost gets a definition because it earns a limited pardon during the walkaround:

Thin hoarfrost is typically a white crystalline deposit which usually develops uniformly on exposed surfaces on cold and cloudless nights.

It is so thin that surface features (lines or markings) can be distinguished beneath it.

The test is built into the definition — if you can read the markings through it, it qualifies. Where that pardon applies (upper fuselage yes, thin frost under the wing tank areas within limits, critical surfaces never) is walked through with the cold-weather ground procedures in article 09. The remaining LIM entries close the chapter's rulebook: rain repellent is reserved for moderate to heavy rain, and the wiper maximum operating speed lives with the speed limitations — 230 kt (article 05).

5. Power: three buses normally, three survivors in emergency

The AMM's power-supply section answers a question every EMER ELEC drill raises — what ice protection is left on the essential network? Per AMM 30-00-00:

When only emergency power is available, these busbars supply electrical power to the equipment shown: (1) AC ESS BUS 901XP: - probe heat, Captain or standby pitot. (2) DC ESS BUS 401PP: - Captains windshield rain repellant. (3) DC ESS BUS 801PP: - Wing Anti-ice System.

The QRH's ELEC EMER CONFIG summary compresses the probe picture into one capitalised line:

ONLY STBY AND CAPT PITOT AND AOA PROBES HEATED

Engine anti-ice does not appear on either list for a good reason — its valves fail open on electrical loss, so it protects without power (at a fuel cost; article 03). One shedding chain is easy to miss: the galley and commercial-load pushbuttons on the electrical panel also carry ice protection. Per FCOM DSC-24-20, setting GALLEY off means Water/Waste (drain mast) ice protection is lost, and the COMMERCIAL pushbutton sheds both the Escape slide lock mechanism ice protection and the drain-mast heating — the chapter's silent subsystems ride on the commercial electrical load (article 07).

6. The cockpit interface map — and a preview of fail-safe directions

Everything the pilot can touch or read for this chapter, on one table (details in the articles listed):

And the single most valuable contrast to pre-load before the systems articles — what each hot-air valve does when the electrical supply dies:

Twenty-eight ECAM alerts belong to this chapter — one of the densest alert families on the aircraft — yet they resolve into just four response patterns: switch sources (probes), isolate (wing), avoid icing conditions, or crew awareness. Articles 11 and 12 sort all of them into those four drawers.

Self-test

[!note]- Q1. What does hot air protect, what does electric heat protect, and why is the split where it is?

Hot air: the four outboard leading-edge slats of each wing and the engine air intakes — large curved surfaces needing area heating, fed from the bleed system. Electric: windshields and windows, the four probe families, and the water/waste heaters — small or scattered elements where wiring beats ducting. "Big surfaces breathe air, small parts run on wire."

[!note]- Q2. Recite the two-sentence definition of icing conditions. Which temperature applies where?

At or below 10 °C — OAT on the ground or after takeoff, TAT in flight — with visible moisture in any form (cloud, fog below 1 600 m visibility, rain, snow, sleet, ice crystals). Also: on the ground and for takeoff, OAT at or below 10 °C while operating on surfaces with snow, standing water or slush that engines could ingest or that could freeze on engines, nacelles or engine sensor probes. Stationary the two temperatures coincide; in flight the hardware feels ram rise, so TAT governs.

[!note]- Q3. What are the four rungs of the chapter's temperature ladder?

10 °C — icing-conditions definition and ice-detection alert window. 8 °C — the AMM's ice-detector inhibition line (taught alongside the 10 °C with the tension flagged). +1 °C — ground engine ice-shedding regime. −40 °C SAT — the climb/cruise engine anti-ice exemption, which descent revokes.

[!note]- Q4. How does the 5 mm figure connect three layers of documentation?

LIM defines severe ice accretion as approximately 5 mm on the airframe; the ice detectors issue their SEVERITY signal after seven elementary detections, calibrated to roughly 5 mm on the wing tips; the abnormal procedures respond to "severe ice accretion" with the VLS +10 kt / green dot minimum-speed and FLAP 3 landing package. Definition → sensor → procedure, one number.

[!note]- Q5. Only emergency power is available. What ice protection survives?

Captain or standby pitot heat (AC ESS), the captain's rain repellent (DC ESS), and the wing anti-ice control circuit (DC ESS). The QRH summary line: ONLY STBY AND CAPT PITOT AND AOA PROBES HEATED. Engine anti-ice needs no power — its valves fail open.

[!note]- Q6. Which way do the wing and engine anti-ice valves fail on electrical loss, and what is each design afraid of?

Wing valves close (fear: uncontrolled heat damaging slats on the ground). Engine valves open (fear: shed intake ice going through the fan). Learn the fears and the directions come free.

Key takeaways

References

Chapter mission, hot-air/electric split and rain-removal means per FCOM DSC-30-10-10. Eleven-subsystem census, supply buses and emergency-power allocations per AMM 30-00-00 (Description and Operation). Icing-conditions definition (both sentences), severe ice accretion, thin hoarfrost and the rain-repellent usage limitation per FCOM LIM, Ice and Rain Protection section; wiper maximum operating speed per FCOM LIM, speed limitations. Emergency probe-heat summary per the QRH ELEC EMER CONFIG summary. Galley/commercial shedding lines per FCOM DSC-24-20. The "temperature ladder", the defence-map framing, the fail-safe-direction table and the four-response-pattern classification are integrative syntheses of the referenced material, developed across the articles cited inline.

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.