An A320ceo departed with a METAR indicating a temperature of -16 °C with freezing fog and a visibility of 600 m. The flight crew did not perform the engine ice shedding procedure, because they evaluated that the aircraft was not affected by ice accretion considering that the visibility was good with no precipitation.

The taxi-out lasted 18 minutes. When aligned on the runway, the flight crew applied a thrust stabilization step of 2 s (50 % N1) as per SOP and then TOGA thrust. During the takeoff roll, the ENG 1 HIGH VIBRATION ECAM alert triggered and the flight crew decided to perform a Rejected TakeOff (RTO) at 61 kt.

The flight crew taxied the aircraft back to the holding point of the takeoff runway and set the parking brake to ON. During 25 s, they gradually increased thrust up to 68 %. They maintained thrust for 6 s until the ENG 1 HIGH VIBRATION and ENG 2 HIGH VIBRATION ECAM alerts triggered. The flight crew put the thrust levers back to idle and decided to return to the parking stand.

During post-flight walkaround, the flight crew visually confirmed significant ice accretion on the fan blades and compressor inlet of both engines. The ground crew performed a manual deicing of the engines using hot air. After that, the flight crew were able to resume the flight. They performed the ice shedding procedure just before takeoff and managed to take off normally.

The METAR indicated a temperature of -16 °C with freezing fog and visibility of 600 m. These conditions were within the criteria of application of the ice shedding procedure provided in the “ENGINE OPERATIONS ON GROUND IN ICING CONDITIONS” section of the FCOM. However, the procedure was not applied before the first takeoff attempt.

The A320ceo aircraft was equipped with CFM56 engines. Because there was freezing fog, the ice shedding procedure for those engines requested that they had to be accelerated to 70 % N1 every 10 minutes, with no hold time.

The taxi-in time of the previous flight, performed in similar conditions, was 4 minutes, and the taxi-out time, 18 minutes. This represents more than two times the maximum time that the aircraft is permitted to be in icing conditions with freezing fog, with engines at ground idle, as described in the FCOM. This overexposure caused significant ice accretion in the engines. This resulted in the strong vibrations felt during the first takeoff attempt. The additional exposure time during the taxi back to the runway holding point most probably enabled additional ice accretion in the engines. This caused the triggering of the ENG 1(2) HIGH VIBRATION ECAM alerts when the flight crew attempted to perform an engine acceleration for ice shedding.

There was no other solution but to return to the parking stand to perform manual deicing.

Ground operations in icing conditions with engines thrust close to ground idle can result in ice accretion on engine components (fig.1). The engine anti-ice system prevents ice accretion on the inlet leading edge, but it does not protect the engine itself. Ice can develop on the fan blades, fan spinner, and first stages of the compressor core.

(fig.1) Example of ice accretion on the fan blades and compressor inlet vanes of an A380 engine during icing tests

Fan blades must be perfectly balanced to prevent asymmetric aerodynamic and centrifugal forces. When ice accumulates and sheds unevenly on these rotating blades, it creates an important imbalance. This imbalance can cause severe vibrations as the engine accelerates, that can result in high-speed RTOs and even engine damage.

The compressor stator blades, that do not rotate, can also accumulate ice. As the engine warms up and core flow increases during the takeoff roll or initial climb, this ice can detach in solid chunks. It can then be ingested into the engine core, causing perturbation of the airflow in the compressor and triggering compressor stall. If the stall occurs at high thrust, it can significantly damage the compressor.

To prevent the above-listed risks, engines must be cleared from ice before takeoff.

Manual deicing of engines must be performed following the dedicated maintenance task from the Aircraft Maintenance Manual (AMM) (or Aircraft Maintenance Publication (AMP) for A220). Depending on the engine type, it can usually be performed using hot air. Deicing fluid must not be used, because it can have a corrosive effect that can cause damage to some engine parts. It can also flow in internal engine parts and freeze.

Ice can also be removed by the flight crew by performing regular engine accelerations at high thrust. This is the principle of the ice shedding procedure.

The conditions to apply the ice shedding procedure are described in the certification requirements EASA CS-25.1093(b)(2), FAA 14 CFR 25.1093(b)(2) and TCCA AWM 525.1093(b)(2). They are included in the Airplane Flight Manual (AFM) when required. The definition of icing conditions and the description of the ice shedding procedure are part of the FCOM of all Airbus aircraft.

A review of Airbus in-service data from 2024 and 2025 indicates that 7 RTOs due to high vibrations and 8 engine stalls during climb with engine damage were reported to Airbus. For those events, the ice shedding procedure was either not applied or incorrectly performed. This highlights a constant safety risk, with significant operational effects that can be mitigated through strict compliance to the ice shedding procedure.

The ice shedding procedure uses the same philosophy across all engine types.

On ground, when operating the engines at or near idle thrust in icing conditions, regular accelerations must be performed. The combination of the induced centrifugal force, the engine speed variations, the increased airflow and the increased temperature from higher thrust will remove the ice from the fan blades and the fan spinner.

Each engine has its own characteristics, and therefore ice shedding procedures must be customized.

Depending on the engine type, the time interval between two engine accelerations, the N1 or EPR target, and the acceleration holding time may vary.

The triggering conditions and the conditions to require maintenance may also vary. All those specificities cannot be listed in this article. Therefore, it is essential to always refer to the FCOM procedure dedicated to your engine type.

At the aircraft level, there are ground icing conditions when the Outside Air Temperature (OAT) on the ground and for takeoff is 10 °C or below, and there is visible moisture. Visible moisture includes clouds, fog with visibility of one mile or less, rain, snow, sleet, and ice crystals.

In addition to ground icing conditions, the FCOM procedure includes other conditions to consider before the application of the ice shedding procedure, depending on the engine type, for example:

• More restrictive temperature conditions
• Type of precipitation (freezing rain, heavy snow, …)
• RVR conditions
• Visibility conditions.

The assessment of the environmental conditions always requires accurate situational awareness, particularly because these conditions can evolve rapidly over time. In addition, some environmental parameters can be measured like temperatures, RVR or visibility, but other parameters like the “visible moisture” rely on pilot perception and can be subject to interpretation.

The quantity of ice accretion depends on the total time the engines are running on ground at or near idle in icing conditions. This includes the taxi-in time of the previous flight, and the taxi-out time, but also any maintenance tasks with engine running must be taken into account.

The time interval between two successive engine accelerations is a maximum time interval, therefore the accelerations can be performed at any time before the time interval elapses. For some engine types, the time counter of the interval between two successive engine accelerations can be reset to 0 if an AMM/AMP task to remove the ice is performed.

For all aircraft, except A350-900 and A350-1000 with specific conditions, a last engine acceleration for ice shedding is requested before takeoff, even if the time interval is not elapsed. The aircraft must be static to perform this pre-takeoff ice shedding. Rolling takeoff cannot be performed.

(fig.2) Example of ice shedding intervals

Before each engine acceleration for ice shedding, careful consideration must be given to selecting an appropriate location.

The flight crew needs to check the ground surface and make sure that the aircraft is in a safe area with no risk associated with the jet blast. Blast diagrams highlighting danger areas can be used to define the hazard zone behind the aircraft. As a conservative approach, the flight crew can refer to the danger areas diagrams for TOGA thrust that are available in the FCOM sections:

• “Procedures / Normal Procedures / Standard Operating Procedures / Engine Start / Ground Run-Up - Danger Areas”, for A300-600, A310, A320 family, A330, A340, A350, and A380 aircraft
• “FCOM 1 / General Information / Aircraft General / Ground Handling / Engine Hazard Areas”, for A220 aircraft.

Ice shedding can be performed on taxiways, but it requires ATC authorization. Because the aircraft must come to a stop, traffic is affected, particularly because a safe distance must be maintained between two aircraft. In the case that the taxiways are too slippery due to ice or slush contamination, the flight crew must coordinate with ATC to find an alternative solution. After making sure that the aircraft is at an appropriate location to perform an engine acceleration, the flight crew must notify ATC before setting the parking brake to ON.

The ice shedding procedure requires a static engine run-up. It cannot be performed at the gate. Airports affected by severe winter operations often assign specific, safe taxiway segments for engine run-ups, but other airports do not always have an appropriate area. Some airports may even prevent ice shedding procedures, because they are not able to provide a location with sufficient safety distance. If appropriate taxiways or run-up areas are not available, the ice shedding procedure can also be performed when aligned on the runway before departure, provided the maximum time interval is not exceeded.

In congested airports, tight departure slots and pressure from ATC to line up and take off rapidly create a high-pressure environment. Performing ice shedding takes additional time creating additional operational pressure, particularly because multiple aircraft may require ice shedding simultaneously. This pressure can increase the risk of errors, because it may cause the flight crew to apply the procedure incorrectly.

To ensure flight crews can safely apply the ice shedding procedure and to prevent too important operations disruptions, airlines need to prepare in advance when possible and work in coordination with airports and ATC. Depending on the airports, manual deicing is still possible by ground crew, but it implies additional costs and additional delays if not anticipated.