(1) Upon the receipt of proper proofs of the death of a member in service on account of which no accidental death benefit is payable under section twelve, there shall be paid to such person as he shall have nominated by written designation duly executed and filed with the board of trustees, otherwise to his estate:
(a) His aggregate contributions at the time of death; and
(b) If the member has five or more years of creditable service, an ordinary death benefit of five thousand dollars ($5,000.00).
(2) The beneficiary of an ordinary death benefit may elect to receive the amount payable in equal installments over a period of years or as a life annuity.