What happened
Following takeoff for a nearby destination, the pilot retracted the landing gear but failed to retract the 20-degree flaps as required by the after-takeoff checklist. While flying at an altitude of approximately 2,400 feet in heavy rain, the pilot observed a power reduction in the right engine. In response to the power dropping to 40 percent, the pilot feathered the propeller, though the flaps remained extended.
Weather conditions at the time included a broken cloud layer at 1,200 feet and scattered clouds at 500 feet. The pilot initially informed air traffic control of the intent to perform an ILS approach, provided altitude could be maintained. However, after maneuvering, the pilot notified controllers that altitude could not be sustained. The aircraft descended to a right base leg, positioned roughly 300 feet above the ground and 0.25 nautical miles from the runway.
The aircraft touched down 6,200 feet down the 8,000-foot runway, with the aircraft tracking approximately 20 degrees to the left. During the landing roll, the aircraft veered off the left side of the runway and exited the airfield through a perimeter fence. Upon arrival of emergency services, the left engine was running at high speed, while the right propeller was in the feathered position. There were no fatalities or injuries reported.
Findings
Investigations revealed that the right engine's power loss could not be definitively attributed to a specific mechanical failure, though rain ingestion was considered a potential factor. Post-accident testing of the right engine in a test cell showed no significant loss of power.
Calculations regarding aircraft performance indicated that the aircraft possessed sufficient climb capability to maintain the necessary altitude for a stabilized approach, even with the flaps at 20 degrees. The failure to properly configure the aircraft by leaving the flaps extended, combined with the engine power loss, contributed to the inability to maintain the required flight path.