Investigation
The final report of the accident blamed it mainly on pilot error; specifically the inability to arrest the high rate of descent existing at 50 ft altitude on the radar altimeter. The descent rate at touch down was 18–20 ft/s. The flight data stored in the volatile memory of the aircraft's Quick Access Recorder (QAR) during the last 500 ft of the approach could not be recovered due to the interruption of the power supply at impact. Probable wind variations and the loss of headwind component, together with the early retardation of thrust levers, led to a 20 kt loss in indicated airspeed just prior to touchdown.
Due to the severe weather conditions forecast for Hong Kong, the flight crew had prepared to divert the flight to Taipei if the situation at Hong Kong was deemed unsuitable for landing. Extra fuel was carried for this possibility, resulting in a landing weight of 429,557 lbs, which is just 443 lbs below its maximum landing weight. Based on the initial weather and wind check which was passed to the crew from Hong Kong during the flight, they believed they could land there and decided against a diversion to Taipei. However four earlier flights had carried out missed approaches at Hong Kong and five had diverted.
During the final approach, the plane descended along the ILS glideslope until at about 700 ft, the crew visually acquired the runway. They disengaged the autopilot but left the autothrottle on. During the flare, the rate of descent was not arrested, the plane landed with the right wing slightly lower. The right landing gear touched down first, the right engine impacted the runway and the right wing was detached from the fuselage. Since the left wing was still attached, the lift from that wing rolled the fuselage onto its right side, and the plane came to rest inverted in the grass strip next to the runway. The spilled fuel caught fire.
Several suggestions were given to China Airlines concerning its training.
Read more about this topic: China Airlines Flight 642