Flytest,
When we want to measure the aircraft to be sure it is airworthy, especially in flight, we don't use the HUMS. We use a level A software Bearing Monitor Unit, which has the redundancy, integrity and internal logic to be trusted with this critical info. A normal HUMS, like the kind mandated by the CAA, is not of the integrity to generate a pilot inflight warning, after all, that warning, if false, could actually cause a worse incident by alarming the crew to do something rash, like ditch.
We have gone round on this before. The typical HUMS is not of a level of airworthiness that allows us to trust it with real time warnings, it is useful as a keeper of times and conditions, a general guide for establishing trends, and a way to require post flight preventative maintenance to be performed.