A pilot must obtain landing clearance prior to landing.  Normally the airport controller will initiate landing clearance without having first received the request from the aircraft; however, should this not occur, the onus remains upon the pilot to request such clearance in sufficient time to accommodate the operating characteristics of the aircraft being flown.  NORDO and RONLY aircraft shall be considered as intending to land when they join and conform to the traffic circuit.  Landing clearance will be given on final approach.  If landing clearance is not received, the pilot shall, except in case of emergency, pull up and make another circuit.