JFZ90,
It is worth noting that 10-7 would be well into the broadly acceptable category so the risk wouldn't even need to be reduced to ALARP - it already exceeds the acceptable risk threshold.
Not necessarily. If you consider the EXAMPLE in 00-56 (because it is only an example although many projects followed it, and from Iss 2), then a Catastrophic event with a probability of 10-7 would be a Class A risk.
One has to be careful in considering the overall aircraft target versus individual system / hazard targets.
sw