20 CFR § 220.187 - If the annuitant's medical recovery was expected and the annuitant returned to work.

If the annuitant's impairment was expected to improve and the annuitant returned to full-time work with no significant medical limitations and acknowledges that medical improvement has occurred, the Board may find that the annuitant's disability ended in the month he or she returned to work. Unless there is evidence showing that the annuitant's disability has not ended, the Board will use the medical and other evidence already in the annuitant's file and the fact that he or she has returned to full-time work without significant limitations to determine that the annuitant is no longer disabled. (If the annuitant's impairment is not expected to improve, the Board will not ordinarily review his or her claim until the end of the trial work period, as described in § 220.170.)

Example:

Evidence obtained during the processing of the annuitant's claim showed that the annuitant had an impairment that was expected to improve about 18 months after the annuitant's disability began. The Board, therefore, told the annuitant that his or her claim would be reviewed again at that time. However, before the time arrived for the annuitant's scheduled medical reexamination, the annuitant told the Board that he or she had returned to work and the annuitant's impairment had improved. The Board investigated immediately and found that, in the 16th month after the annuitant's began, the annuitant returned to full-time work without any significant medical restrictions. Therefore, the Board would find that the annuitant's disability ended in the first month the annuitant returned to full-time work.