A320 Wing Icing

[Sparky08]

Is it correct to assume, that when in up to moderate icing conditions, the A320 wing anti-icing system is designed to and effective enough to prevent ice on the wing? Or is it a possible case of ice forming and shedding being acceptable?

Thoughts appreciated.

sparky

[alatriste]

ICING

Sparky:

The FCOM requires the activation of Wing Anti-ice System (WAI) whenever is an indication of airframe accumulation. The WAI can be used to prevent any ice formation (anti-ice) or to remove an ice accumulation from the wing leading edges. The AFM recommends avoiding extended flight in icing conditions with extended slats/flaps, as accreted ice may block the retraction of them causing mechanical damage.
If WAI works properly, protected areas (heated) are not suceptible to build up any ice.

Try to find out more info in "getting to grips with cold weather operations" from Airbus. ( www.airbus.com- pilots/briefing notes OR www.smartcockpit.com- flight ops)

REGARDS from sunny Spain.

[safetypee]

Sparky08, the conclusion to your assumption might be correct, but the logic may be reversed; see the following extract from UK AIP; Icing definitions.

• Light - The rate of accumulation might create a problem if flight in this environment exceeds 1 hour. Occasional use of de-icing/anti-icing equipment removes/prevents accumulation. It does not present a problem if de-icing/anti-icing equipment is used.
  
  
• Moderate - The rate of accumulation is such that even short encounters become potentially hazardous and use of de-icing/anti-icing equipment, or diversion is necessary.
  
  
• Severe - The rate of accumulation is such that de-icing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is necessary.

From these definitions, conditions of moderate icing are defined by the aircraft’s de-icing/anti-icing capability. Ice accumulations or further icing should be removed / prevented for short encounters. If ice is not being removed / prevented then the conditions are severe and you should get out of them PDQ.
The interesting and important aspect of these definitions is that the icing conditions which the aircraft experiences may not be the same as the forecast met definitions and certainly not the same as expected from PIREPS unless it is from the same aircraft type.

[Sparky08]

Thank you for your comments. My question is based in an understanding that the intent of anti ice systems is to prevent ice formation when icing conditions are suspected or actually encountered. Hence the term Anti ice vs. De-ice system.

That being said, does it have a secondary intended design function as a de-icing system, in the event icing accretion takes place before the system is selected on? Of course it is used as such when tactically required but I am trying to understand if the "late to activate" use, in the case of A320, is actually part of its design function.

Thanks again.

[nnc0]

I think de-ice means just that - get rid of accumulated ice/snow. On something like a Dash 8 with pneumatic boots it's strictly a de-ice system. The ice forms and the boots inflate/deflate to shatter/dislodge the formed ice on a set inflation cycle.

On the A320 the anti-ice bleeds will serve for de-iceing and anti-icing.

[krujje]

Didn't ATR manage to certify the de-icing boots on the -42 and -72 as anti-ice systems in the 80's and 90's?

[safetypee]

Sparky08, I believe that your understanding (#4) is correct, but it would be subject to the precise (certification) interpretation. Unfortunately CS25 does not help very much, but the quote below suggests that there is no primary or secondary function; – just operate the system i.a.w manufacturers procedures and as the situation requires.

AMC 25.21(g) A1.2.3 Ice accretion prior to normal system operation.
“Ice protection systems are normally operated as anti-icing systems (i.e. designed to prevent ice accretion on the protected surface) or de-icing systems (i.e. designed to remove ice from the protected surface). In some cases, systems may be operated as anti-icing or de-icing systems depending on the phase of flight.”

I do not know about late activation use in the A320, but in some aircraft this term relates to the system capability, e.g. a fully evaporative anti-icing system selected on after ice had accumulated is ‘de-icing’. However, due to the restricted capability of some anti-icing systems (as a deicer) or a high rate of ice accumulation, might lead to some runback ice. Then there are systems which have an additional boost capability or procedure to remove the runback ice, or alternatively the boost is used in specific configurations, again where the basic anti-icing system might have limited capability or the rate of ice accumulation is high, e.g. approach and landing. Thus in these aircraft a late activation procedure is part of the design function.

CS 25 Large Aircraft.

[lomapaseo]

There is a fuzzy transition between ant-ice (prevent ice formation) and de-ice (shed ice that has formed). In the former there is necessarily a thermal balance inferred between the ice accretion on a cold metal surface with a warm inside surface. Under severe icing conditions some ice is anticipated to accrete even when the inner surface is heated due to the temperature gradient across the thickness. However as ice accretes it adds insulation and decreases the temperature gradient across the thickness thus raising the outside surface to close enough to melting that the ice blanket now sheds (de-ice). The idea behind the certification standards is to control this balance within anticipated icing conditions to where any accumulation is shed before it seriously affects the performance of the aircraft or engine.

Some of the shortfalls in this are:

Runback ice (melting from the heatload and flowing away from heated surfaces) ) can track from a benign location in-flight to a much more critical location.

Icing conditions on the ground are not always considered in the certification, since they are not part of a flight envelop (just don't dispatch)

Remember ground icing conditions are what the aircraft and the engine feels, not what you feel on the ground. So be wary of cold metal surfaces that you wouldn't want to stick your tongue to and above freezing moisture

Some ice sheds may find their way to the engines and cause a multi-engine loss of power.

[Clandestino]

Is it correct to assume, that when in up to moderate icing conditions, the A320 wing anti-icing system is designed to and effective enough to prevent ice on the wing?

Yes - but only on the heated parts of the wing (i.e. outboard slats). Inboard portions are not that critical.

is it a possible case of ice forming and shedding being acceptable?

Shedding of the wing ice when wing anti-ice is turned on is acceptable, but with bleed air thermal de-ice, there is no ice accretion while it's working and therefore no ice shedding after the initial one.

Didn't ATR manage to certify the de-icing boots on the -42 and -72 as anti-ice systems in the 80's and 90's?

Nope. De-icing boots on the ATR will shed ice during inflation cycle, not all of it, but what's left or what grows on wings between the cycles doesn't hurt performance (or stability) much. Up till 2003. procedure was to turn on electrycal anti-ice if propellers ant flight controls horns as you entered icing conditions (TAT<10°C and visible moisture) and turn on engine and wing de-icing when ice accretion was detected (i still miss that PING! sound on bus) or observed. De-icing was to be turned off when ice accretion stopped. This was changed and new procedure was to turn off de-icing after leaving icing conditions. Needles to say, number of patches on our boots went up. Allegedly FAA has even tried to make turning on engine boots every time prop anti-ice was turned on, but as I never flew N-registered machines, I'm not certain what happened with this proposal.

Cheers, C. (2500hrs on ATR and 650hrs on A320)