Icing Operations I — Ground De-Icing and Holdover Time

An aircraft under snow is not dirty — it is wearing armour that destroys lift (article 10 covers the clean-wing aerodynamics). This article is about taking that armour off and dressing the aircraft in a time-limited raincoat — anti-icing fluid — plus everything the cockpit must do while the spray happens. Of all ATA-30 operations, this is where the captain's personal authority weighs heaviest. The engine's own ice (fan and core) is a separate war fought in article 09; the airborne story is article 10.

1. Who decides — and the fluid chemistry they decide with

The procedure's first sentence is an assignment of responsibility. Per the FCOM adverse-weather supplementary procedures:

In all situations, it is the responsibility of the captain to decide if the ground crew must deice/anti-ice the aircraft, and/or if additional deicing/anti-icing treatment are required.

And the basis of the decision is personal inspection. Per the FCTM cold-weather chapter:

When icing conditions on ground are encountered, and/or when ice accretion is suspected, the Captain should determine, on the basis of the exterior inspection, if the aircraft requires ground deicing/anti-icing treatment. This visual inspection must take into account all vital parts of the aircraft, and must be performed from locations that offer a clear view of these parts.

De-icing and anti-icing are different verbs. De-icing removes what has already frozen on; anti-icing lays a fluid film against what has not yet fallen. The fluids split the labour — per the FCTM: Type 1 is low-viscosity, short holdover, mainly for de-icing; Types 2, 3 and 4 are high-viscosity, long-holdover, dual-purpose. High viscosity is a double-edged requirement, and the FCTM's mission statement for the fluids captures both edges:

Deicing/anti-icing fluids must be able to remove ice and to prevent its accumulation on aircraft surfaces until the beginning of the takeoff. In addition, the fluids must flow off the surfaces of the aircraft during takeoff, in order not to degrade takeoff performance.

A coat that clings through the snow shower yet shears cleanly off under takeoff airflow — otherwise you'd be departing with self-applied contamination. The application methods:

‐ In one step, via the single application of heated and diluted deicing/anti-icing fluid: This procedure provides a short holdover time, and should be used in low moisture conditions only. The holdover time starts from the beginning of the application of the fluid. ‐ In two steps, by first applying the heated deicing fluid, then by applying a protective anti-icing fluid: These two sprays must be applied consecutively. The holdover time starts from the beginning of the application of the second fluid.

[!warning]- Holdover time starts when spraying begins, not when it ends Halfway through the spray, the first-treated surfaces are already spending their protection — so the clock starts at the earliest exposure, conservatively. And the tables that convert fluid type and precipitation into minutes are explicitly advisory. Per the FCTM: The holdover time starts from the beginning of the application of the fluid, and depends on the type of fluid, and on the nature and severity of precipitation. The flight crew should refer to applicable tables as guidelines. These tables must be used in conjunction with the pre-takeoff check. Guidelines — the snow can out-fall the table, and the final referee is always eyes on the wing (§3).

One more chemistry rule with a memorable logic — per the adverse-weather procedures, if repeated anti-icing becomes necessary, the ground crew must deice the surfaces with a hot fluid mixture before applying a new layer of anti-icing fluid. A spent anti-ice layer is water-saturated gel; painting fresh fluid over it seals the failed coat underneath. Take the wet raincoat off before putting on a dry one.

2. Before the spray: seven cockpit steps and the DITCHING trick

The skeleton (adverse-weather procedures; action lines paraphrased): establish communication with the crew doing the spraying → check the fluid type against operator requirements → do not start engines during spraying → CABIN PRESS MODE SEL checked AUTO → both ENG BLEEDs OFF and APU BLEED OFF → DITCHING pushbutton ON → thrust levers checked idle → tell the ground crew "AIRCRAFT PREPARED FOR SPRAYING". Note the nuance on engines — per the procedure's own note, Engines and APU can be either stopped or running during deicing/anti-icing — running is fine; starting mid-spray is not.

Two cautions ride with the spraying itself:

Do not move flaps, slats, ailerons, spoilers or elevators if they are not free of ice.

Always ensure that both left and right side of the aircraft receive the same complete and symmetrical deicing/anti-icing treatment.

Symmetry has no exceptions — even a local frost patch on one wing buys a symmetrical treatment of both (per the procedure's note, the captain may request local de-icing of affected areas but shall take care that both wings receive the same symmetrical treatment). Asymmetric surface roughness is asymmetric stall behaviour.

Switching both engine bleeds off with engines running has a scripted side effect:

Note: If both engines are running, the AIR ENG 1+2 BLEED FAULT alert triggers when both ENG BLEED pb-sw are set to OFF. If this occurs, disregard this alert.

(The bleeds close so the packs cannot inhale fluid mist — an ATA-36 favour to ATA-21.) And then the clever step. DITCHING — the water-landing seal button — is borrowed as a fluid seal:

Outflow valves, pack flow control valves, avionics ventilation overboard valve close. This prevents de-icing fluid from entering the aircraft. Avionics ventilation is provided by operating cabin fans, since air blows to the inboard valve. Considering the low OAT, there is no time limitation associated with this configuration.

Three attached notes are all exam-worthy: forget to switch it off and it will lead to lack of pressurization in flight, and ultimately trigger the CAB PR EXCESS CAB ALT alert; the outflow-valve and lavatory/galley-vent alerts that appear while sealed are expected — disregard; and passenger comfort suggests not running both packs off on the ground beyond about 20 minutes.

3. After the spray: a code, two waits, one ice patrol

The probe-region trap — this caution describes a mechanism, not just a rule:

When the OAT is low (below -5 °C) during snow/freezing rain precipitations and with crosswind conditions, melted snow or raindrops may drip from the cockpit windshields and freeze on the fuselage below. Ice may then build up and possibly disturb the airflow around the static/pitot/angle-of-attack probes, and result in unreliable air data measurements during takeoff. Therefore during taxi out before takeoff beware of this possible build up of ice. The area around static/pitot/angle-of-attack probes must be free of ice/snow before starting takeoff.

Trace the chain: window heat (article 05) melts the snow → meltwater runs onto unheated skin below → refreezes into ridges upstream of the probes → corrupted airflow → unreliable air data on the takeoff roll. Every system working exactly as designed, combining into a hazard — and the seed of the ice-ridge/spurious-stall-warning story in article 11.

The anti-icing code. The report the ground crew owes you, per the same procedure — The information from ground personnel who performed the deicing and post-application check must include (ANTI-ICING CODE): • The type of fluid used • The ratio of fluid to water (e.g. 75/25) • The time of the holdover beginning — plus the post-application verdict that the aircraft's critical parts are clean. Fluid type and dilution select your holdover-table column; the start time sets the clock.

DITCHING off, with a small trap for the stationary case: confirm on the ECAM pressurisation page that the outflow valve reaches open — and if spraying was done engines-off:

If spraying is performed with the engines not running, a small negative cabin delta P may appear for a short time, just after selecting the DITCHING pb-sw to OFF. During this time, do not open any doors or windows.

Two waits before restoring bleed air — at least 1 minute after spray completion for the engine bleeds, and at least 5 minutes for APU bleed, with the reason attached:

Note: There is a risk of deicing fluid ingestion by the APU air intake, resulting in specific odors, or smoke warnings. Therefore: ‐ Keep the APU running with the APU bleed off for 5 min after spraying completion before setting the APU bleed to on (if required), ‐ Consider takeoff with APU bleed off.

(The APU inlet sits on the fuselage where atomised fluid lingers longest — hence five minutes against the engines' one. Fluid odour in the cabin afterwards connects to the smoke-procedure smell signatures of article 05.)

And the closing law of the whole business:

Apply appropriate normal procedures. Pay special attention to the flight control check. In freezing precipitation, perform the appropriate checks to evaluate aircraft icing. Base the decision on whether to takeoff, or to re-protect the aircraft, on the amount of ice that has built up on the critical surfaces since the last de-icing, as revealed by a personal inspection from the inside and outside of the aircraft. Make this inspection before the holdover time expires, or just before takeoff.

[!warning]- Holdover time unexpired ≠ cleared for takeoff The criterion is never the clock; it is the state of the critical surfaces, established by personal inspection. The holdover table is an alarm clock telling you when to go and look — an expired HOT doesn't automatically mean re-spray (look first), and an unexpired HOT doesn't authorise departure through a heavy shower (look anyway). This is what "tables used in conjunction with the pre-takeoff check" means in practice.

4. Taxi to the de-icing bay: the five interlocks

When the aircraft taxis contaminated to a remote pad, the after-start flow adds five prohibitions, all reading "…until the aircraft is deiced":

One sentence version: on a frozen aircraft, touch nothing that moves. Spray, confirm clean, then run the after-start items.

5. The fluid's electronic side effect: radio-altimeter ghosts

De-icing fluid on the radio-altimeter antennas produces one of the stranger ground phenomena. Per the adverse-weather procedures:

On the ground with contaminated surfaces or deicing fluid on radio altimeter antennas, the radio altimeters may indicate some erroneous values or no values.

If the PFD displays erroneous radio altimeter values, the flight crew can disregard the triggered auto callouts and/or the GPWS/EGPWS alerts.

An aircraft calling "RETARD" on the parking stand is not haunted — it is a belly antenna reading through a film of glycol. Undue calls can appear at the stand, during taxi, and on the takeoff or landing roll; with no values on either side, the radio-altimeter fault alerts may equally be disregarded. Recovery comes when the aircraft leaves the contaminated surface or the film flows off. The bottom line is a positive check: confirm radio-altimeter values are displayed on the PFD before entering the runway — the entire low-altitude protection stack (GPWS modes, auto callouts, landing logic) stands on that sensor.

6. Where the cockpit meets the paperwork

The de-icing question actually opens at aircraft acceptance, not at the spray pad: reviewing the technical log and MEL items (article 13) tells you whether today's aircraft is even allowed into icing conditions; and in icing conditions at or below +1 °C, acceptance includes reading the previous crew's freezing-fog taxi time out of the logbook — an input the engine ice-shedding clock of article 09 consumes. The spray procedure itself is the textbook case of a read-and-do task: per the FCTM's operating philosophy, not-routine actions like airframe de-icing are performed from the written procedure, not from memory. The captain's three personal decision points stay personal: whether to treat, local or full treatment, and — after the last look at the wing — go or re-protect.

Self-test

[!note]- Q1. Define de-icing versus anti-icing, and the two fluid families.

De-icing removes accumulated ice/snow (Type 1 — low viscosity, short holdover, hot); anti-icing prevents new accumulation (Types 2/3/4 — high viscosity, long holdover, also usable for de-icing). The fluids must protect until takeoff begins, then shear off cleanly in the takeoff run.

[!note]- Q2. When does holdover time start for one-step and two-step procedures — and what is the one-step restriction?

One-step: from the beginning of the (single) application; low-moisture conditions only. Two-step: from the beginning of the second fluid's application, the two sprays applied consecutively. Either way, the clock starts at first exposure, not completion.

[!note]- Q3. What does DITCHING ON close, why, and what are the three attached gotchas?

Outflow valves, pack flow control valves and the avionics overboard valve — sealing the hull against fluid ingestion, with avionics cooling carried by cabin fans (no time limit at low OAT). Gotchas: left ON it blocks pressurisation in flight (EXCESS CAB ALT); the sealed-configuration valve alerts are expected — disregard; both packs off on the ground is uncomfortable past ~20 minutes.

[!note]- Q4. Explain the below-−5 °C windshield-meltwater trap.

Heated windshields melt snow; the meltwater refreezes on the unheated fuselage below, building ridges that disturb airflow around the static/pitot/AOA probes — unreliable air data on takeoff. The probe region must be verified free of ice and snow before takeoff.

[!note]- Q5. Why one minute for engine bleeds but five for APU bleed after spraying?

Ingestion risk scales with where the inlet sits: the APU intake lives in the lingering fluid mist, so the procedure keeps the APU running bleed-off for 5 minutes (and suggests a bleeds-off takeoff from the APU's standpoint); engine bleeds wait only 1 minute. APU ingestion announces itself as odd smells or smoke warnings.

[!note]- Q6. The five interlocks for taxiing to a de-icing bay — and the principle behind them?

No ground-spoiler arming, no trim movement, no flap-lever movement, no flight-control check, after-start checklist delayed — all until fully deiced. Principle: on a frozen aircraft, touch nothing that moves.

[!note]- Q7. What must be confirmed about the radio altimeters before entering the runway, and why?

That the PFD shows radio-altimeter values. Fluid on the antennas can blank or corrupt them (ghost callouts may be disregarded on the ground), but GPWS, auto callouts and landing logic all stand on the RA — don't take off with it silent.

Key takeaways

References

Captain's responsibility, repeat-anti-icing rule, no-engine-start note, surface-movement and symmetry cautions, local-frost note, bleed/DITCHING sequence with its three notes, probe-area caution, anti-icing code items, negative-delta-P caution, bleed-restoration timing with the APU ingestion note, and the personal-inspection closing law per the FCOM adverse-weather supplementary procedures (airframe de-icing/anti-icing on ground); five de-icing-bay interlocks per the same chapter's after-start section; radio-altimeter behaviour and disregard authority per its contaminated-airports section. Fluid characteristics, one-step/two-step methods, holdover definition and captain's-inspection basis per the FCTM cold-weather chapter; read-and-do philosophy per the FCTM operating-philosophy chapter. Aircraft-acceptance links per the FCOM cockpit-preparation SOP. The raincoat framing, the meltwater-chain narrative and the alarm-clock reading of HOT 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.