The Board of Trustees shall grant an ordinary disability retirement allowance to a member if: the member has at least 5 years of eligibility service; and the medical board certifies that: the member is mentally or physically incapacitated for the further performance of the normal duties of the member’s position; the incapacity is likely to be permanent; and the member should be retired. This subsection applies only to a member of the Employees’ Pension System who: is promoted within the Department of Corrections to a position that no longer is eligible for membership in the Correctional Officers’ Pension System as provided in § 25-201 of this article; elects not to transfer the years of creditable service the individual accrued in the Correctional Officers’ Retirement System to the Employees’ Pension System; and is eligible to receive a vested allowance from the Correctional Officers’ Retirement System. A member may combine the eligibility service accrued in the Correctional Officers’ Retirement System and the Employees’ Pension System to determine if the member is eligible for an ordinary disability retirement allowance under subsection (a) of this section from the Employees’ Pension System.