I don't recall seeing a specific reference in the "new" comptroller handbook series, but if you have a copy of the OLD Comptroller's Handbook for Fiduciary Activities, (the one with the green cover)look at on page 36, bottom left column.
It says: "The bank, as trustee, must have a program of appraisal and inspection of all real estate held in accounts where the bank has investment responsibility. The appraisal program must require appraisals at least every three years for real properties held in personal trust accounts. In the case of real properties held in employee benefit accounts and collective investment funds, appriasals should be performed at least annually. The inspection program must require the inspection of real properties at least as often."
As I recall, the annual inspection and triennial appraisal was never specifically required by regulation, but more or less falls under the risk and management of trust assets. Also **IMPORTANT** the appraisal requirement for doesn't say anything about the appraisal meeting any USPAP standards or having to be completed by a credentialed appraiser.
If you think about it, what they are looking for is to make sure the TTEE is evaluating the real estate on a regular basis to see if it continues to be 1) an appropriate investment for the trust; 2) it is income producing (or if it'snot you can justify why not - as in the case of a grantor's residence); and 3) is the continued retention of the real estate consistent with the needs and requirements of the trust.