An insurance cut is an additional trim-out of material made after the removal of initially assessed damage boundaries.
Usually an insurance cut is specified as 0.040".
There are several reasons for insurance cuts to be specified in a repair plan:
If damage such as corrosion or gouges / notches have been found and removed by trimming, insurance cuts help ensure that the full extent of damage has been removed. For example, if corrosion was beginning to exfoliate or had penetrated beyond boundaries which can be easily identified with inspection to the desired POD. Or if the time since damage is unknown it is possible that a crack could be developing at a gouge or nick which again, may not be detectable within typical statistical reliability.
If there is damage which has been known to have been present for a span of continued operation before it was documented, the insurance cut can help "zero-time" the damage from a fatigue perspective. In a similar manner to how things like fastener holes having undergone a period of load cycling might be oversized to a specific size when installing a repair or modification to help "zero-time" the installation.
Basically, an insurance cut does what it says on the can... it removes additional material as an insurance of damage removal.
This is an extremely common step in virtually every repair plan I have seen or written in the context of post-production support for aircraft.
Oh, then it's an "assurance" cut, then, not an "insurance" cut.
But shortly all the English majors will come out from behind the shop benches and correct me.
