Originally Posted by
212man
I think you have jumped to a conclusion that does not bear close scrutiny. I think the only scenario your comment holds true for, is that the floats were armed but there was a fault in the electrical circuit that prevented the AFDS from functioning, where a second Batt Bus circuit would/might have mitigated. Given that we have established that the Generators remain on line (and hence the DC Buses are powered) down to 80% Nr, I find it completely implausible that this aircraft touched down with the Nr below that value, with the absence of damage we see.
I've never done an engine off landing in an S92, but surely it is not beyond the bounds of possibility that a frantic hauling up of the collective with no engine power could not dip the Nr below 80% just before water impact? I suppose there is also a question of how long it takes for the alternators to go off line and bus ties to open once the Nr gets below 80%. It won't be instant but it might be quite quick.
It is all speculation of course, but I maintain that it is bad design to have an ultimate last resort life saving device not powered by the ultimate last resort electrical power source. What justification would there be for not having a supply from the battery to the float switches? It is not as if there could be any significant power drain in normal operation. And it does seem odd that there is a CB for manual float inflation on the battery bus, but the blurb posted suggests that this doesn't include powering the float switches. It all seems rather odd.
Do you know what the logic is for the float switches? Does it require any one switch, or both switches to be activated?