11 Pa.C.S. § 12002

The chief of police shall be designated by the mayor from within the ranks and may be demoted without cause in the same manner, but not to any rank lower than the rank which was held at the time of designation as chief of police. In the event that no qualified officer from within the ranks has applied for the designation, the chief of police shall be designated by the mayor from outside the ranks. The officers, other than the chief of police, shall be designated in accordance with Chapter 144 (relating to civil service).