A long way above is a post that lllustrates the rate that when the temperature is only just below freezing ice can accumulate on an aircraft, the person who was flying an aircraft with a far less critical wing entered cloud at 5000 ft in the decent and control was almost lost until the aircraft entered warm air and the ice melted. Being daylight and with full cooperation from ATC who had been put fully in the picture, disaster was narroly averted.
To me this looks simply like and aircraft that was flown into icing conditions that proved far beyond the capabilities of the aircraft to shed the ice and a pilot who failed to appreciate the rate that ice can accumulate.