WPR19FA093 · Piper PA23 250

While descending from cruise altitude toward the destination airport, the pilot reported to air traffic control that he needed to divert to a closer airport because the left engine was "misfiring" and that he was going to "shut it down." Radar data indicated that the airplane flew toward the diversion airport and continued to maneuver south past the airport, where radar contact was lost around 700 ft mean sea level. The airplane subsequently impacted a lake about 1/2 mile west of the airport. Data from the airplane's engine monitoring system revealed a drop in left engine exhaust gas temperature (EGT), cylinder head temperature (CHT), and fuel flow values near the end of the flight. These values then increased again for a few minutes before decreasing a second time. The left engine fuel flow value for the last 3 minutes of the data was 0, and the left propeller was found in the feathered position, consistent with the pilot having shut down and secured the engine in flight. Review of the airframe maintenance logbook indicated that several airframe-related fuel system components were replaced during the 4 months before the accident. An entry in the left engine logbook about 4 days before the accident stated that the left engine No. 5 CHT was fluctuating and that a loss of 300 rpm was experienced when testing the right magneto in flight; however, this issue could not be duplicated on the ground, and the airplane was returned to service. Fuel residue was observed on and around the left engine's electric fuel pump. The pump was removed and functionally tested, during which two leaks were found during pressure tests; however, the effect of these leaks on engine operation could not be determined. No other anomalies of the airframe fuel system were observed; however, the system was heavily fragmented and had been submerged in water for several days before recovery. Based on the available information, the reason for the reported loss of engine power and the extent to which the left engine may have been able to continue to produce power could not be determined. Additionally, the reason for the pilot's low-altitude maneuvering in the vicinity of the runway could not be determined; however, it is likely that the pilot failed to maintain airspeed while maneuvering for landing with the left engine inoperative, which resulted in a loss of control and impact with water.

Verbatim NTSB analysis and probable cause from the NTSB dataset