Accident Summary
While descending to Tauranga Airport in poor weather conditions, a twin-engine aircraft struck the slope of Mount Ngatamahinerua, located 30 km west of Tauranga Airport. The aircraft was destroyed and all 23 occupants were killed.
Investigation Findings
The official investigation determined that the probable cause of the accident was a strong downward current in the lee of the Kaimai Range close to the Gordon quarry. This downward current carried the aircraft below the level of the crests of the range. Under the conditions prevailing at the time, the aircraft then encountered an area of extreme turbulence in which it was impossible for the pilot to regain effective control and recover height.
Contributing Factors
Several contributory causes were identified. First, the captain of the aircraft was unaware of his true position and initiated a premature descent. However, it was noted that he descended only to the level officially designated as the minimum safe altitude in the area of his descent. Second, the Civil Aviation authorities had classified the Kaimai Range as non-mountainous terrain for the purpose of determining the safe altitude for the route. Third, the forecast of the upper wind between Whenuapai and Tauranga was misleading.