CEN13FA267 · Beech 58

The pilot and the pilot-rated passenger were preparing to depart from an airport where the twin-engine airplane had just undergone refurbishment of the interior. The pilot stated that both engines started normally. They taxied to the runway and used the checklist to perform an engine run-up on both engines. The pilot said the engine run-up was normal. He then lined the airplane up on the runway, applied full power to each engine (red line is 2,700 rpm), and departed. Once airborne, the pilot initiated a right turn. The pilot said that, when the airplane was at an altitude of between about 1,200 and 1,400 feet, he brought the propeller controls back to 2,500 rpm and left the power on both engines at 30 inches of manifold pressure. The mixture controls remained full forward. Almost immediately after reducing the rpm, the pilot heard a "faint" and indistinguishable "pop" from the left engine. Both engines simultaneously went from "full power" to idle, but the manifold pressure remained at 30 inches. The pilot said he made an immediate turn back to the runway and landed gear-up on the grassy area adjacent to the departure runway threshold.

A postaccident examination of the airplane revealed only minor damage to the right wing, left horizontal stabilizer, and fuselage. The propeller blades also exhibited slight twisting, which was consistent with them rotating at the time of impact. Several slash marks made by the propellers were observed in the grass where the airplane made the forced landing. The measured distance between these marks was consistent with both engines operating between 1,570 and 1,890 rpm at the time the propellers contacted the ground.

Data from the onboard engine monitor, which recorded exhaust gas temperature (EGT), cylinder head temperature (CHT), and turbocharger turbine inlet temperature on each engine, were downloaded and plotted. The data revealed that the left engine lost power several seconds before the right engine. A rise in EGT was observed at this time as well. According to the engine manufacturer, if the mixture control were leaned, it would have decreased the mechanical fuel pumps' fuel flow and might have caused the smooth rise in EGT. However, the CHT continued to climb for several seconds after the decline of EGT on both engines. The data also indicated that the EGT appeared to rise again slightly before the data ended. The pilot reported that he did not move the mixture control at any time during the short flight. Due to the engine monitor's limited parameters (no rpm or fuel flow data), a conclusive cause for the power loss could not be determined. Examination of the airplane's fuel, electrical, and flight control systems revealed no preincident mechanical deficiencies that would have led to a loss of engine power. Both engines were examined then test run on the airframe using the airplane's fuel system. No mechanical deficiencies were identified that would have contributed to a loss of engine power.

Verbatim NTSB analysis and probable cause from the NTSB dataset