Thanks Steve, though I am not quite sure whether that counts as an incident or an event. Its always a bit alarming when you have to do what the aircraft wants to do rather than what you want to do, but did you think that safety was compromised? I suppose it could have been, in that the descent might have put you in conflict with other traffic, but apart from that it seems to show that the "system" works despite encountering severe icing.
I've now seen a copy of the flight manual RIPS section - it seems like a good system, though its not fully duplex in that the blade heating elements, though zoned, are not duplexed, which I guess is why Nick went silent when I asked if there were any single point failures that could bring the system down. The flight manual includes the information that in the event of a failure of an element, out-of-balance vibration may occur with instructions to "vacate icing conditions". As I mentioned previously it may be impossible to vacate icing conditions safely if you have embarked on a flight in IMC where freezing and cloud level are below MSA, so I suppose the wisdom of doing that would depend on how severe the vibration is likely to be.
HC