There is no Fixed Asset Impairment feature in Dynamics GP per se but that doesn't mean that I can't be done. The simplest way to accomplish a full or partial Fixed Asset impairment is do a full or partial retirement of the asset in GP and create a retirement code to identify impairments. Since GP supports partial retirement by cost or % this will work for assets that contain multiple quantities in GP.
For example, a $100,000 assets is impaired and is now only worth $60,000. The company can partially retire 40% of the asset (or specifically retire $40,000) and take a loss.
The nice thing about this is that it's easy to un-retire an asset. While Generally Accepted Accounting Principles (GAAP) won't allow you to un-impair an asset, International Financial Reporting Standards (IFRS) will. As the world moves toward IFRS, the ability to un-retire an asset and recapture the impairment becomes more important. It's also nice if you goof when retiring the asset.
For reporting purposes, using an impairment retirement code makes it easy to separate out impairment transactions from true retirements.