Convair 580 ZK-KFU was scheduled for 2 regular return night freight flights from Christchurch to Palmerston North. At 20:32 flight 642 started its takeoff from runway 20 on schedule and climbed to FL210. The flight progressed normally. At 21:13 the Wellington controller cleared the flight to descend initially to FL130 and later to FL110. After contacting Ohakea Control the crew were further cleared down to 7000 feet and were given vectors for the approach to Palmerston. The aircraft descended through an area of forecast severe icing, which was probably beyond the capabilities of the aircraft anti-icing system to prevent ice build-up on the wings and tailplane. The aircraft then probably stalled because of a rapid build-up of ice, pitching the aircraft nose down and probably disorientating the crew. Airspeed increased to 392 kts and the G loading was peaking at 3.21 G. The angle of bank was probably between 50ø and 60ø. Increasing torsional stress on the wing roots probably caused panels to buckle and separate. At an altitude of 6800 feet the wings and engines started to separate. Nine seconds later the remaining fuselage impacted the sea about vertically and at high speed. PROBABLE CAUSE: The TAIC accident investigation report did not contain a probable cause.