Lyman,
I think we are looking at this from different perspectives. You make some interesting points, but you may have read too much into my simplistic observation. I well remember getting very seriously iced-up in strato-cumulus on an (empty) C-47 in my misspent youth. We ended up with ice about an inch thick over the whole of both unheated windshields, and - when that had later melted enough for us to see through a hole in same - there was a stalagmite-like horn sticking forward about 6 inches from the frame between the two. The ice seemed to have propagated gradually backwards along both sides of the nose (I don’t recall noticing any ASI problems). When we eventually landed, there was still a circular area of glaze ice about 3 ft in diameter below the centre of the nose.
Now the characteristics of ice in strato-cumulus at an IAS of 120kts and TAT of just below freezing may be very different from those in cirrus or Cb at, say, IAS 280kts and TAT MS30C. And I don’t know how much research has been done into how much accretion there is on the nose in the latter circumstances. Although the heated windshields usually remain fairly clear (in my experience), except in heavy precipitation, you can see very little of the fuselage skin from the cockpit. It may be that the heated pitots and, usually further back, the AoA vanes can ice up before the unheated nose skin. But I doubt it.
When I ask if it’s a good idea for numbers 1 and 2 in each case to be positioned exactly symmetrically on the left and right sides respectively, I’m assuming that aircraft are normally flown with zero sideslip. Therefore, if both installations are serviceable and identical, they are likely to accumulate any ice in unison (unless the sun is shining from the side). You say that turbulence is required, but I presume that would even out in zero sideslip?
You suggest that the positioning of probes is arbitrary, which I doubt. But I’m sure you have noticed that the positions of numbers 1 and 2 mirror one another? And, when I ask about pre-AF447 accidents related to probes (heated as designed, and not damaged or blocked by any foreign object), I’m not limiting the question to Airbuses.
N.B.
Once again: are we discussing this on the wrong thread?
[EDIT]
Have reposted this on the Rumours & News A330/A340 EAD (AoA PROBES) thread. Thanks Turbine_D.
Last edited by Chris Scott; 7th Jan 2013 at 00:24.