20 C.F.R. § 225.20
The Survivor Tier I PIA and the Employee RIB PIA are used in computing the tier I component of a survivor annuity. The Combined Earnings PIA, Social Security Earnings PIA and Railroad Earnings PIA may be used in computing a vested dual benefit offset in the survivor tier II component when the survivor tier II is based on a percentage of the employee annuity tier II. In addition, these three PIA's are identical to those dual benefit PIA's used in computing an employee retirement annuity, as described in subpart B of this part, when the employee died after being entitled to an annuity. Survivor annuity computations are discussed in part 228 of this chapter. The Residual Lump-Sum PIA (RLS PIA) is used in computing the amount of the residual lump-sum payable when retirement annuity payments were made, as explained in part 234 of this chapter.
20 C.F.R. § 225.20