The crew (pilots and technicians) were engaged in a local test flight consisting of an electric equipment post maintenance check. After liftoff, while in initial climb, the seaplane encountered difficulties to gain height, stalled and crashed in flames in an open field. Both pilots were killed while three other occupants were seriously injured. The aircraft was destroyed.
Probable cause (official findings): Inadequate preflight preparation on part of the crew who failed to obtain/maintain flying speed at takeoff. It was determined that the airplane stalled due to an excessive accumulation of ice on airframe. At the time of the accident, approximately 50% of frost accumulated on aircraft that was not de-iced prior to takeoff. Mineral research and electric test flight.