All original appointments to positions as fire apparatus operators shall be for a probationary period of six months, but during the probationary period an appointee may be dismissed only for a cause specified in section thirteen of this act or because of incapacity for duty due to the use of alcohol or drugs. If at the close of the probationary period the conduct or fitness of the probationer has not been satisfactory to the appointing body or officer, the probationer shall be notified in writing that he will not receive a permanent appointment, and the appointment shall cease. If the probationer is not notified or dismissed in accordance with this section, his retention shall be equivalent to a permanent appointment.