"Consider a supplementary defined benefit plan with the following features: [1] Unit accrual pattern: No cost leveraging from final average salary designs. [2] Later benefit accruals: Plan participation would not begin before age 45. [3] Later benefit commencement: No earlier than age 75. [4] Life annuity options only: Single life option for single participants and 75 percent joint and survivor option for married participants. [This] plan structure ... forms the basis for a longevity plan. The first two features address employer cost and volatility concerns. The [last two] features ... address longevity risk."