(a) Tier I. The tier I benefit of a parent annuity ends with the earliest of the last day of the month before the month in which the parent—

(1) Dies;

(2) Becomes entitled to an old age benefit under the Social Security Act that is equal to or larger than the tier I benefit of the parent annuity before any reduction for the family maximum, unless he or she is also entitled to a tier II benefit (reduction for the family maximum is discussed in part 228 of this chapter);

(3) Becomes entitled to another survivor annuity in a larger amount, unless he or she elects to be paid the smaller annuity; or

(4) Remarries after the employee's death, unless he or she marries a person who is entitled to Social Security or Railroad Retirement Act benefits as a divorced spouse, widow, widower, mother, father, parent, or disabled child.

(b) Tier II. The tier II benefit of a parent annuity ends with the earliest of the last day of the month before the month in which the parent—

(1) Dies;

(2) Remarries after the employee's death; or

(3) Becomes entitled to another survivor annuity in a larger amount, unless he or she elects to be paid the smaller annuity.