Authorities in Iceland do not rule out a technical problem or human error as cause of the accident. Iceland's RNF have opened an investigation into the accident.
Sukhoi reported the aircraft was conducting test flights to evaluate the CAT IIIa automatic landing system on one engine in strong crosswinds. 3 flight crew and 2 certification engineers were on board. One of the certification engineers received a leg injury during evacuation.
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Source: avherald.com; flightglobal.com; aviation-safety.net