Accident Overview
The flight from Wellington to Picton-Koromiko Airport was uneventful until the pilot began a descent in good weather conditions. While on final approach at an altitude of 1,700 feet, the single-engine aircraft entered clouds and struck the slope of Mt Robertson, located 10 nautical miles northeast of Blenheim. The aircraft was destroyed.
Casualties
All five occupants were killed, and the pilot was seriously injured.
Probable Cause
The official investigation reported the following causal factors: the pilot's decision to descend beneath the cloud layer; illusions created by the conditions producing misleading visual references; misidentification of distant terrain features; an undetected heading error and loss of positional awareness; insufficient forward visibility during the later stages of the descent; the high speed of the aircraft; and the pilot's decision making, including a delayed decision to descend beneath the cloud layer and continued flight into deteriorating conditions. Contributing factors included the pilot's familiarity with the area creating a false sense of security; improved general weather conditions causing the pilot to relax; a possible false horizon created by a sloping cloud base; and the absence of documented procedures to ensure pilots crossed the coast south of Rarangi.