Upon subsequent retirement, his retirement annuity shall consist of:
The total retirement annuity shall not, however, exceed the maximum applicable to the member at the time of original retirement. In the computation of any such retirement annuity, the time that the member was on retirement shall not interrupt the continuity of service for the computation of final average compensation and the additional membership service shall be considered, together with service rendered before the previous retirement, in establishing final average compensation.
A person who re-enters the service of a department within 3 years after retiring may qualify to have the retirement annuity computed as though the member had not previously retired by paying to the System, within 5 years after re-entry and prior to subsequent retirement, in a lump sum or in installment payments in accordance with such rules as may be adopted by the Board, an amount equal to all retirement payments received, including any payments received in accordance with subsection (c) or (d) of Section 14-130, plus regular interest from the date retirement payments were suspended to the date of repayment.
40 ILCS 5/14-111