Icing Operations II — Engine Ice Shedding and Cold-Weather Ground Operations

The spray rig of article 08 handles the airframe — but the ice growing inside the engines is beyond its reach. Engine anti-ice heats only the intake lip (article 03); the fan blades, spinner and core stators run bare, and their de-icer is brutally simple: run the engines up and throw the ice off. Around that one action the manuals build a clock-and-temperature regime, and a dedicated ECAM alert welds it into the aircraft. This article also closes out the ground story: the cold-weather walkaround, cold-soak parking, and the water-draining decision. The airborne narrative follows in article 10.

1. The threat: ice the anti-ice can't touch

Per the FCOM adverse-weather supplementary procedures (engine ice shedding on ground):

During engine operations on ground in icing conditions, and with the OAT at or below 1 °C (34 °F), ice accretion may affect the fan and core engine parts.

[!warning]- Engine anti-ice ON does not prevent this ice EAI heats the intake lip skin only. Fan blades, the spinner and the compressor stators have no heating at all; at ground idle the airflow is slow, centrifugal force weak, and moist freezing air packs ice steadily onto cold rotating metal. The two harvest paths: fan ice sheds and strikes blades or enters the core (FOD), and stator ice chokes the flowpath — a surge or damage risk exactly when takeoff power is applied. That second path has its own alert (§4).

The dose is time — per the same section, The quantity of ice accretion depends on the time during which the engine is running on ground in the above-mentioned icing conditions. The whole regime is therefore an ice timesheet. The remedy is acceleration: spool up and let centrifugal force, blade flexing and airflow shear evict the build-up. And note the threshold: +1 °C here versus the 10 °C definition of article 01 — the third rung of the temperature ladder. Ten degrees marks where icing conditions may exist; one degree marks where a parked, running engine demonstrably grows ice.

2. The clock: this leg inherits the last leg's debt

The two windows are defined to the minute:

The taxi-out time starts when the first engine is running, and finishes when the aircraft is aligned on the departure runway for takeoff. The taxi-in time starts at touchdown, and finishes when both engines are set to off.

[!warning]- Your acceleration allowance starts partly spent Ice does not vanish at engine shutdown. Whatever grew during the previous crew's freezing-fog taxi-in is still on the fan an hour later — so the preliminary cockpit preparation reads the logbook: Check the recorded running time of the engine on ground with FZFG for: • The taxi-in time of the previous flight • Any running time of the engine on ground associated with a maintenance activity. The allowance table then subtracts it: with freezing fog, the maximum time to the next engine acceleration is 45 minutes minus (previous taxi-in plus maintenance running); without freezing fog, 60 minutes minus the same. If maintenance de-iced the engines before start, the debt is cleared — per the procedure, If the engines are deiced with an AMM task before engine start, disregard the recorded running time of the engine on ground — and the full 45/60 minutes are yours. Changing weather rounds against you: If the OAT changes, the flight crew must consider the lowest temperature.

The bookkeeping is symmetric: parking in freezing fog, you record this leg's taxi-in time (or the time since the last shedding run-up) in the logbook — the next crew's opening balance. And it starts before you board: the aircraft-acceptance flow in icing conditions at or below +1 °C explicitly includes reading that figure (article 08 closed with the same hook).

3. Three grades of shedding run-up

Every run-up shares a fixed preamble — check the ground surface and the area behind, notify ATC, hold the aircraft on brakes — under a standing warning:

Before and during the application of the procedure, ensure that the jet blast due to the increased thrust is not a hazard to people or installations behind the aircraft.

Then the grades (action values summarised from the procedure; each run-up ends by retarding to idle — and if the aircraft starts to move during the run-up, the levers come back to idle immediately):

The gradient teaches itself: colder plus foggier grows harder ice faster, so the answer escalates — more N1, longer holds, tighter intervals — until, below −20 °C in freezing fog, mechanical shedding is no longer trusted at all and the only exit is maintenance de-icing: Return to the gate to request the deicing of the engines in accordance with the AMM. The same exit applies when the clock expires unservable:

CAUTION If the ground surface conditions or the environment do not permit the application of the procedures when reaching the maximum taxi time to next engine acceleration: cancel the takeoff.

(A 50 % N1 run-up on a glazed taxiway is its own emergency — hence the caution.) Housekeeping: taxi time in freezing fog beyond 30 minutes gets its own logbook entry, and taxi-in mirrors taxi-out — same table, count reset to zero after each shedding run-up, request gate de-icing when the environment defeats you.

4. The pre-takeoff iron rule — and the alert that counts for you

The flight crew must perform a final engine acceleration before takeoff to remove ice accretion from the engine (regardless of any engine acceleration performed during the taxi-out).

Lined up, held on brakes, 50 % N1 for 10 seconds (in icing conditions at or below +1 °C) — and then the line in capitals:

DO NOT PERFORM ROLLING TAKEOFF

The physics: a rolling takeoff merges the shedding event with the takeoff itself, so the ice lets go at full power and full inhale — the worst possible ingestion. A static run-up sheds the ice at moderate power and zero ground speed, and takeoff thrust is then applied to a clean fan. If the runway itself can't host the run-up, the procedure allows it before line-up in an area offering both better friction and jet-blast clearance.

The regime's electronic enforcer is an alert discovered in the engine abnormals — ENG RISK OF STATOR ICING:

This alert triggers if all the following conditions are satisfied: ‐ OAT below 1 °C ‐ Engine anti-ice set to ON ‐ Cumulative engine idle time since the previous landing above 40 min ‐ No engine core de-icing procedure performed. This alert is reset if: ‐ The aircraft is in flight, or ‐ The engine core de-icing procedure is performed.

Its procedure is one line — in freezing fog, apply the core de-ice procedure, with the reference pointing straight back to this chapter's ice-shedding section.

[!warning]- One of the trigger conditions is anti-ice ON Read the four conditions again: the alert fires with engine anti-ice on. EAI ON is not a talisman here — it is merely the system's evidence that you really are sitting in icing conditions, while the alert watches the ice EAI cannot reach: the stators. And the 40-minute counter runs since the previous landing — the last leg's debt (§2), kept electronically by the FADEC ecosystem. The alert converts a crew discipline into a monitored quantity: forget to count, and the engine counts for you.

5. Taxi discipline: 10 kt, no single-engine taxi, flaps up

The FCTM's contaminated-taxiway package, key sentences verbatim:

On contaminated taxiways, the taxi speed should be limited to 10 kt, and any action that could distract the flight crew during taxiing should be delayed until the aircraft is stopped.

At speeds below 10 kt, the antiskid is deactivated

Ten knots is also where your braking becomes purely tyre-versus-surface. Add the quieter items: engine anti-ice raises ground idle (so speed control is a deliberate act), avoid large tiller inputs, and on slippery surfaces differential braking and thrust can steer better than the nosewheel. In prolonged holds the FCTM restates the shedding habit with a tell-tale attached:

‐ In icing conditions: When holding on ground for extended periods of time, or if engine vibration occurs, thrust should be increased periodically, and immediately before takeoff, to shed any ice from the fan blades.

"Or if engine vibration occurs" — vibration on the ground is ice already unbalancing the fan, the ground edition of the airborne suspicion test in article 12. Single-engine taxi is banned outright in this regime:

One engine taxi is not permitted in icing conditions with OAT at +1 °C (34 °F) or below (due to ice accretion and the required engine acceleration during the ice shedding procedure).

(The shut-down engine would grow ice with no way to shed it — you would be pre-loading a contaminated start or takeoff.) Flap timing joins the family — per the after-start SOP, taxiing in icing with rain, slush or snow:

Maintain the flaps retracted until the aircraft reaches the holding point of the takeoff runway. This action prevents contamination of the slats/flaps mechanism.

And when the after-start checklist reaches its anti-ice line, the FCTM's scripted response set is the neat summary of the whole panel: the pilot flying checks the WING and ENG pushbuttons and answers "OFF", "Engines ON", or "Engines ON Wings ON." Takeoff-performance side notes that belong to this picture (developed in articles 10 and 13): FLEX thrust is prohibited on contaminated runways (derated thrust may be used), anti-ice use carries its performance penalty — and the last line of defence is the FCTM's: Before the aircraft lines up on the runway for takeoff, the flight crew must ensure that the airframe has no ice or snow.

6. Cold-weather ground operations: the walkaround and the cold start

Safety exterior inspection extras (action lines summarised): protective covers removed; APU intake, pack inlet/outlet doors, outflow valves and pressure-relief valves checked free of snow and ice, de-iced as necessary. Preliminary cockpit preparation in deep cold:

Note: 1. Ground power should be used to start the APU if the OAT is -15 °C (5 °F) or below. 2. With cockpit temperatures below -15 °C (5 °F), the display units may not be available.

For temperatures at or below -15 °C (5 °F) in the avionics bay, the IRS alignment requires 15 min.

A cold-soaked jet boots slowly — plan the turnaround around a quarter-hour alignment. The windshield gets its own caution, the twin of article 08's probe trap:

With ice or snow accumulated on the windshield and/or the upper cockpit fuselage, and if the PROBE/WINDOW HEAT is on, melted ice or snow running down from these areas could re-freeze on the fuselage area below, if the temperature is very low. This could create ice build-up on the forward fuselage that could possibly disturb the airflow around the static/pitot/angle-of-attack probes.

Hence the order of operations: clear the snow above first, then switch the heat on. Probe covers come off before the pushbutton — per the procedure, Ensure that the probe covers are removed in order to prevent them from melting — then PROBE/WINDOW HEAT ON (back to AUTO after the first engine start).

The walkaround proper — the critical-surfaces sentence, verbatim:

Check critical surfaces: leading edges, upper wing surfaces, vertical and horizontal stabilizers, all control surfaces, slats and flaps.

Two legal allowances, both from article 01's definitions: Thin hoarfrost is acceptable on the upper surface of the fuselage, and On the underside of the wing tank areas, a maximum layer of 3 mm (1/8 in.) of frost is acceptable (cold-soaked fuel frost — the mechanism appears in article 10). The engine items include one that surprises first-timers:

Check that engine fans are not stuck and can rotate freely.

Overnight slush frozen at the fan root will fight the starter — spin the fan by hand before asking the starter to. Plus: drains, bleeds and probes clear; fuel-tank vents, radome and lower nose fuselage clear; and the water system checked not frozen and refilled — with the note that commercial water should have been previously emptied prior to aircraft cold soak, which hands over to §7.

7. Cold soak: parking the aircraft for a freezing night

The definition, verbatim:

Cold soak should be considered in the following conditions: ‐ The OAT is less than 0 °C (32 °F), and ‐ No electrical supply and no air conditioning are provided to the aircraft, and ‐ The temperatures of aircraft components decrease below 0 °C (32 °F).

The securing flow, with each step's logic: after all bleeds off and before AC power off, DITCHING ON (the same borrowed seal — this time against snow entering the outflow valve; after battery-off it goes back OFF, since the valves reopen at next power-up). Chocks in, then:

Releasing the parking brake prevents the brakes from freezing.

(Moisture between hot discs freezes them into one lump overnight.) Captain's seat fully forward — To ease access to the avionics bay, since seat operation becomes difficult once the mechanism is cold-soaked — covers requested for wheels, engines and probes; water draining requested; and the harshest line for the coldest nights:

If the APU battery is subject to a cold soak for 12 h or more and the ambient temperature is below -15 °C (5 °F), its remaining capacity may not allow the cold-soaked APU to start. Remove the battery and store it in a warm place.

One parking-time footnote: early in a cold soak the green-reservoir underfilled alert may trigger from transient fluid-temperature differences — check the quantity sits in the upper half of the normal band before assuming a leak.

The drain decision is a table (reconstructed from the water-system draining procedure):

Which is article 07's "anti-ice, not de-icing" turned into operations: power and heat are the water system's protection — remove them, and you empty the pipes. The draining procedure itself is ground teamwork (service-panel handle to DRAIN, indicator lights, and in freezing temperatures the drain valves stay open afterwards by design — caps off, panel doors unclosable, all intentional).

Self-test

[!note]- Q1. Where does ground engine ice grow, and why doesn't EAI prevent it?

On the fan blades, spinner and core stators — EAI heats only the intake lip. At ground idle, slow airflow and weak centrifugal force let moist freezing air pack ice onto the unheated rotating and static hardware.

[!note]- Q2. Define taxi-out and taxi-in times, and explain the "last leg's debt".

Taxi-out: first engine running until aligned on the departure runway. Taxi-in: touchdown until both engines off. Ice survives shutdown, so the freezing-fog allowance (45 min; 60 min without FZFG) is reduced by the previous flight's taxi-in and any maintenance ground-running — read from the logbook at acceptance; cleared only by a maintenance de-ice.

[!note]- Q3. Recite the three run-up grades and the below-−20 °C verdict.

No freezing fog: 50 % N1 for 10 s, every ≤ 60 min. Freezing fog, −7 to +1 °C: 50 % N1 for 60 s, every ≤ 45 min. Freezing fog, −20 to −7 °C: 70 % N1 for 50 s, every ≤ 45 min. Freezing fog at or below −20 °C: no run-up offered — cancel the takeoff and have maintenance de-ice the engines.

[!note]- Q4. Why is a rolling takeoff forbidden after the final shedding run-up?

A rolling takeoff merges shedding with departure: ice releases at full power and maximum ingestion. The static run-up sheds at moderate power and zero speed, so takeoff thrust is applied to a clean fan — that is the entire point of "regardless of any acceleration performed during taxi-out".

[!note]- Q5. The four trigger conditions of ENG RISK OF STATOR ICING — and why is "anti-ice ON" among them?

OAT below 1 °C; engine anti-ice ON; cumulative idle time since the previous landing above 40 minutes; no core de-icing performed. Anti-ice ON is the system's evidence of real icing exposure — the alert guards the stator ice EAI can't reach, and its 40-minute counter is the last-leg debt kept electronically. Reset: get airborne, or do the core de-ice.

[!note]- Q6. Why is single-engine taxi banned at or below +1 °C in icing conditions?

The shut-down engine accretes ice with no means of shedding it (run-ups need the engine running) — you would be storing up a contaminated start or takeoff. Both engines run, both get their run-ups.

[!note]- Q7. Name the cold-soak securing steps that most often surprise, and their reasons.

Parking brake released once chocked (prevents brake freezing); captain's seat fully forward (avionics-bay access before the mechanism stiffens); DITCHING ON until battery-off (seals the hull, reopens at power-up); APU battery removed to a warm store after 12 h below −15 °C (a cold-soaked battery may not start a cold-soaked APU); water drained per the table — heaters prevent, they don't thaw.

Key takeaways

References

Threat statement, accretion-time dependence, taxi-time definitions, logbook debt and subtraction table, lowest-temperature note, jet-blast warning, three run-up grades with repeat intervals, gate-return exits, expired-clock caution, final-acceleration rule, rolling-takeoff prohibition, off-runway alternative, taxi-in mirror and parking record per the FCOM adverse-weather supplementary procedures (engine ice shedding on ground). ENG RISK OF STATOR ICING trigger, reset and procedure per the FCOM engine abnormal procedures. Cold-weather inspection additions, APU ground-power note, display-unit and IRS cold notes, windshield-meltwater caution, probe-cover rationale, critical-surfaces list, hoarfrost and 3 mm allowances, fan-rotation check and water-system checks per the FCOM adverse-weather ground-operations section; cold-soak definition, securing steps, APU-battery rule, reservoir note and water-draining table and procedure per its securing and water-draining sections. Taxi speed, antiskid threshold, periodic-thrust habit, single-engine-taxi prohibition and line-up assurance per the FCTM cold-weather and taxi chapters; checklist responses per the FCTM normal-checklists chapter; flap-retention line per the FCOM after-start SOP. The timesheet framing, the gradient reading and the "engine counts for you" formulation 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.