20 C.F.R. § 225.22
The Employee Retirement Insurance Benefit PIA (Employee RIB PIA) is used to compute the employee RIB amount when the employee had received a retirement annuity which was reduced for early retirement. As explained in part 228 of this chapter, the employee RIB amount may be used in the survivor tier I component. This PIA is computed in accordance with section 215 of the Social Security Act using the deceased employee's combined railroad and social security earnings. The Employee RIB PIA is the same as the Survivor Tier I PIA when the employee had no earnings in the year of death. Earnings in the year of death are used in the recomputed PIA beginning January 1 of the year after the employee's death. (See subpart F of this part for a discussion of PIA recomputations.)
20 C.F.R. § 225.22