The crew was conducting a series of circuits and landings. The check pilot was sitting in the right hand control seat and was holding the checklist. During the circuit in question, the check pilot spent a considerable amount of time discussing various aspects of the aircraft operation. There was further cockpit talk during the final approach, and neither pilot realised that the landing gear had not been lowered. The aircraft slid on its belly for some 360 metres after touchdown. No fault was subsequently found with the aircraft or its systems. The gear warning horn was serviceable, but had probably been deactivated by the pilot when power was reduced in the early stages of the circuit. To re-arm the warning system, the power levers have to be advanced to about 30 torque. The particular circuit was being flown with the flaps up, and was probably conducted at a power setting lower than that required to effect re-arming. The pilot in the left seat had experienced minor difficulties in handling the aircraft as precisely as desired, and the check pilot had assumed an instructional role. Under these circumstances, the normal two-pilot challenge and response method of conducting the various pre-landing checks had broken down.