What happened
Following the completion of an annual inspection, the owner of the aircraft elected to perform a maintenance test flight. During the flight, the pilot shut down the right engine to test the propeller by feathering and unfeathering it; the engine was successfully restarted using a windmill technique.
The pilot then attempted the same procedure on the left engine. However, after feathering the left propeller, the propeller failed to unfeather, preventing the engine from restarting. The aircraft continued the flight with only one engine operating.
Upon returning to the airport, the pilot attempted to extend the landing gear during pattern entry, but the gear failed to deploy. In response, the pilot initiated a go-around. During this maneuver, the aircraft failed to climb and began losing altitude. The aircraft eventually collided with the ground off the airport during an unarrested descent.
The investigation
The investigation determined that the landing gear extension and retraction system was hydraulic in nature and powered by a pump located on the left engine. Because the left engine could not be restarted, the hydraulic pressure required for normal gear operation was unavailable. While the flight manual provided two alternative methods for emergency gear extension, the pilot did not attempt either of these procedures during the initial landing approach.