Asset with a cost of $1,000 has a useful live of 5 years. At the end of year 2, the NBV will be $600. At this point of time, there is impairment on this asset and it has to be written down to $450. An unplanned depreciation of $150 will be posted. Subsequently, the assets should be depreciated at a rate of $150/year for the remaining 3 years. However, current SAP configuration calculates depreciation based on the initial acquisition costs (in this case it will be based on $1,000 which will have an annual depreciation of $200/year and the asset will be fully depreciated before the end of Year 5.
A way is needed in which the asset written down will be depreciated based on the new cost basis ($450). Maybe a unique depreciation key is usable.