20 C.F.R. § 225.23
The Combined Earnings PIA used in survivor annuities may be used in computing the tier II component when the survivor tier II is based on a percentage of the employee annuity tier II and the employee had been or would be, if he or she were still alive, entitled to a vested dual benefit. If the employee received a retirement annuity before death, this PIA is identical to the retirement Combined Earnings Dual Benefit PIA described in subpart B of this part. If a retirement annuity was not paid before the employee's death, the PIA is determined as if the employee were 65 years old in the month of his or her death. The Combined Earnings PIA used in survivor annuities is determined in accordance with section 215 of the Social Security Act as in effect on December 31, 1974. It is computed using the deceased employee's combined railroad and social security earnings after 1950 (or after 1936 if a higher PIA would result) through December 31, 1974.
20 C.F.R. § 225.23