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Pitot icing

Old 30th May 2009, 23:42
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Pitot icing

If you were to experience pitot icing in a jet transport would you expect all your pitot systems to be affected,and what temperature/humidity conditions would cause this assuming the pitot heating was fully operational/
Airbus say that this phenomena can happen in equatorial regions near TS but I cannot believe it would happen in Northern Europe in May???
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Old 31st May 2009, 00:03
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I guess in every area with severe icing condition, you could get your pitot system frozen otherwise in a jet airliner is difficult to get ice in the pitots
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Old 31st May 2009, 00:50
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By fully operational, do you mean no fault messages?

I can't imagine anything which can burn your fingers in a second to freeze over.

Manual or automatic anti-ice?
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Old 31st May 2009, 01:55
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NSEU, keep imagining.
tubby linton et al, “…would you expect all your pitot systems to be affected…”
The problems which I am familiar with involved the TAT probe (fully heated), and has been observed in association with engine malfunctions due to unusual icing conditions (refs below).
In unusual circumstances, the atmospheric temperature and water/ice content of the air flowing through the TAT probe can match the heat flow of the heater. Thus, ice can form in the probe resulting in a ‘high reading’ of zero degrees (same as the ice).
IIRC there have been rare events involving some pitot probes, which if blocked will lock in the pressure conditions present at that time. Presumably, in the same conditions all systems could be affected simultaneously.
N Europe in May? – Yes, see the maps for the problem locations!

AIRA - Collaborations - Propulsion System Icing
SAE Aircraft & Engine Icing International Conference: 2007 Session Presentations
http://www.skybrary.aero/bookshelf/books/581.pdf
http://www.flightsafety.org/asw/jun0...n08_p12-16.pdf
AERO - Engine Power Loss in Ice Crystal Conditions
Airline Regulators Grapple With Engine-Shutdown Peril - WSJ.com
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Old 31st May 2009, 09:11
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Nseu,yes I meant no failure messages on Ecam.The problem I experienced was on one air data system producing erroneous data.Airbus are saying it was probably pitot icing but the failures we had affected both the speed and altitude indications.Some of the subsystems recognised that the data was faulty others didn't.
I should also add that there was no evidence of any airframe icing whilst this was occurring.
Thank you for the links

Last edited by tubby linton; 31st May 2009 at 09:41.
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Old 31st May 2009, 14:01
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Fly MD , No pitot icing problems!!
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Old 31st May 2009, 23:29
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tubby , I do not know about the specifics of Airbus, but in many modern aircraft the ADC may use both pitot/static inputs.
In some cases, gross pressure differences will flag an ADC error or shut the system down. In other situations, those systems using the ADC output might average, or compare raw data or a combination of data from each ADC, and depending on the system logic, differing displays / warnings might be seen.
In the incident you cite, you may wish to investigate how the effected subsystems use the ADC output and what data type is required. This might isolate which ADC dominated and thus indicate which pitot system (if applicable) was at fault.

For some lateral thinking, you could investigate how the ADCs use TAT. IIRC temperature gets into all sorts of calculations and corrections (Mach etc) and thus a TAT fault might be the root of the indications. I suspect that TAT probe icing is more likely than pitot icing; also if Mach changes in the ADC (TAT trend toward zero), the EFIS IAS will also change.

The detailed in the articles above will explain why airframe icing would not have been present in these rare circumstances, and why very few returns are seen on WXR.

Re “…MD , No pitot icing problems…”
Except when the pitot heaters are not turned on; check for an accident quite some time ago on this subject.
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