Yet we still don't know (nor, for the purposes of this thread, much care) what particular situation Billy is referring to.
But the "raft of different risk assessments", and methods of prioritising the work
etc. is exactly what we are interested in.
Meanwhile, in further addressing the OP:-
1) Unavailability of equipment
2) In use
3) Not found
Here are some suggestions:-
1) Arrange to carry out the PM when the equipment
is available (weekends, evenings, night-time
etc.)
2) See 1) above
3) Remove item from the inventory