Sequence of Events
During the first cargo flight of the day, the first officer reported that the left engine propeller control was not working properly. The captain indicated they would shut down the airplane and contact maintenance if the issue could not be resolved before the return flight.
For the return flight, both engines started normally, and the propellers were cycled. The crew successfully reset the left propeller control, and the airplane departed with the first officer as the pilot flying. The takeoff and initial climb were normal.
As the airplane climbed through 4,000 feet, the left engine propeller control stopped working, and the power became stuck at 2,400 rpm. The captain attempted to adjust the propeller control and inadvertently increased power to 2,700 rpm. He then took control, leveled off at 4,500 feet, canceled the IFR flight plan, and proceeded VFR toward the destination airport, which was about 160 nautical miles away. The first officer suggested returning to the departure airport, but the captain chose to continue. The first officer did not challenge this decision.
When the flight began descending to 1,500 feet, the right engine began to surge and lose power. The crew performed the engine failure checklist, and the captain feathered the propeller and shut down the engine. Shortly afterward, the left engine also began surging and losing power. The captain ordered the first officer to declare an emergency.
The airplane continued descending and impacted the water "violently" approximately 32 miles east of the destination airport. The captain was unresponsive after impact, and the first officer could not lift him from his seat. As the cockpit filled rapidly with water, the first officer grabbed the life raft and exited through the separated tail section.
Aftermath
The first officer did not know what caused both engines to lose power. The airplane was not recovered from the ocean, preventing examination and testing to determine the cause of the engine failures.
Operator's Statement
According to the operator, the flight crew should have landed as soon as practical after the first sign of a mechanical issue. The crew should have diverted to the closest airport when the left engine propeller control stopped working, rather than continuing toward the destination.