Argentinian investigators have provisionally concluded that a Saab 340A suffered serious icing and entered a stall from which it failed to recover before crashing in the south of the country.
None of the 19 passengers and three crew members survived the accident, which occurred while the Sol Lineas Aereas turboprop was en route to Comodoro Rivadavia on 18 May.
Flight 5428 had departed the city of Neuquen and was climbing through 17,900ft. Cockpit-voice recorder transcripts, released by investigation agency JIAAC, show that the two pilots watched and commented on ice formation for several minutes.
"It is like we were getting ice impact in all places," one of them said, adding a few seconds later: "It builds a lot. It builds more than it sheds."
They discussed a descent to 14,000ft and continued to mention the spread of ice to various parts of the airframe, before alerting to deteriorating speed and sudden vibration.
A stall warning and bank angle alarm sounded and, about 40s later, having failed to regain control of the Saab, the pilots issued a Mayday.
Satellite images identified an extensive weather front over Patagonia at 20:45, around the time when the flight lost contact.
Argentina's weather service, Servicio Meteorologico Nacional, had stated that the probability of icing was "high" between 8,000ft and 19,000ft, said investigation agency JIAAC.
The captain of the flight had 2,187h on type - out of 6,133h in total - while the co-pilot had 288h on type.
JIAAC investigators said there had probably been "inadequate" flight planning and "complacency" by the crew. It pointed out that the pilots had opted to descend in conditions which exacerbated the icing, without looking at possible re-routing or a quick return flight.