The crew of Rescue 312 departed Val D ‘Or, Quebec, Canada, to search for a missing helicopter in an assigned search area between Matagami and Chibougamou. They descended to low-level and conducted a visual search from Chibougamou west to Chapais and then west to a logging camp identified as Camp 8. Enroute to Camp 8, at approximately 750 feet above ground level the left spotter reported a possible contact in a river. The aircraft commander, in the right seat and in control of the aircraft, descended to identify the sighting. After orbiting the river at approximately 400 feet above ground and ascertaining that the reported contact was not the object of the search, the aircraft commander initiated a climbing left turn to regain search track and altitude. The aircraft commander began his left climbing turn at approximately 115 knots. As he turned through 90 he increased the aircraft’s bank angle to 45. During this turn the aircraft experienced what the first officer described as a stall buffet. It is not known whether this stall buffet occurred as a result of the aircraft commander attempting to recover a nose drop during the turn or as a result of using excessive bank angle and “G” loading for the speed available. In either event, from this point to final impact, the crew alternately experienced stall buffet and wing drop. Prior to striking a small hill the aircraft’s right wing tip cut a narrow swath through a cluster of trees 60 feet high. The tree cut indicated a right bank of approximately 40ø. At impact the aircraft was in a nose high attitude with 20ø of right bank established. The ground scars and wreckage distribution indicated slow forward speed with the bulk of destruction occurring as a result of post impact fire. Cause Factors: PERSONNEL PILOT (32A) CARELESSNESS: The aircraft commander did not exercise due care in ensuring that the aircraft remained within its operation envelope during low level SAR manoeuvring while at the controls of the aircraft. PERSONNEL PILOT (32A) TECHNIQUE: The aircraft commander failed to take effective stall recovery action. PERSONNEL OTHER FLT. CREW INATTENTION: The first officer did not adequately monitor airspeeds nor advise the pilot when the airspeed decreased below a safe margin