N.Y.C. Admin. Code § 15-104: § 15-104 Probationary period.

Preliminary to a permanent appointment as firefighter there shall be a period of probation for such time as is fixed by the civil service rules, and no person shall receive a permanent appointment who has not served the required probationary period. The service during probation shall be deemed to be service in the uniformed force if succeeded by a permanent appointment, and as such shall be included and counted in determining eligibility for advancement, promotion, retirement and pension.