212man - thanks for the offer of the rfm pages, I would appreciate a look-see and I can wait til the 23rd!
As you say, one option is to fly out of the icing conditions but if you make it a requirement to have somewhere to go, surely you are back in the realms of the limited icing clearance and so the full de-icing isn't giving you much advantage?
On the other hand, if the rfm (any rfm, not just the 92's) allows you, for instance, to fly in icing conditions in a mountainous region where surface temperatures are below zero and cloud base is well below msa, but its not a fully duplex system, surely that's a gotcha if (when) it fails?
TOD - interesting that the airbus only has a simplex system. Of course you make a fair point that you are normally above all the crap that we mortals fly in, but if the system fails at cruising FL, and you are above 8/8 icing clouds, how do you comply with the flight manual?
Answering my own question, perhaps you have the range / speed to go somewhere else where there isn't 8/8 icing clouds?
And I suppose it could be argued that the fixed wing system should be more reliable as surely its easier to de-ice bits when they are not whirling round and round!
To 212's other points I would say that you should have the ability to cope with a single failure but not a double. ie you should not fly above float vne with the system armed, as a single failure (the firing system) would cause you a problem. However if not armed, its OK to fly above that speed (just as well on a SKY machine!) as you would have to have a problem with both the arming and the firing systems (assuming a well designed system!) before a problem occured. But with the Vne power off, its OK to fly above that because you would have to have a double simultaneous engine failure for there to be a problem and that is extremely unlikely. Perhaps not impossible but then consider where the limit comes from? I don't know that answer but perhaps it is just because that is as far as the test pilots wanted to go with no engines and an eyewatering rate of descent, or because the handling at that speed is not nice. But its probably not because anything catastrophic would happen in the few seconds it took to lose the speed. But inflating floats above float Vne could be catastrophic in various ways such as the floats ripping off and hitting rotors, or an uncontrollable pitching up/down etc. Not a very scientific analysis I know so I'll stop now!
HC