ERA13FA131 · Cessna T337C

Shortly after taking off on the test flight, the pilot transmitted "mayday mayday" over the control tower's radio frequency. According to eyewitnesses, the airplane was in a left-wing-down attitude when it impacted a tree, power lines, and then another tree before coming to rest in a pasture. A review of data downloaded from the engine data monitor revealed that the rear engine exhibited erratic fuel flow beginning 2 days before the accident and continuing through the accident flight. Further, the engine data monitor indicated that the rear engine's propeller was under low-to-no power with a low pitch angle at the time of impact. The front engine exhibited no abnormalities or malfunctions, and the investigation found no other anomalies that would have precluded normal operation of the airplane.

During postaccident examination, the engine-driven fuel pump was removed and bench tested where it exhibited fuel flow higher than manufacturer guidelines with low fuel pressure. In order to meet bench test standards, an adjustment equal to three turns of the adjustment screw was made. The fuel pump then operated normally and was placed back on the engine; however, the engine still did not attain full power. Further examination revealed potential debris between the throttle assembly's brass and stainless steel plates. After removal of the debris and reassembly of the throttle assembly, it operated within the normal range. Although the source of the debris could not be definitively determined, it likely originated in either in the fuel or a fuel tank.

Maintenance records indicate that two days before the accident, the fuel pump was removed, repaired, and reinstalled after work was completed on the rear fuel selector valve. After the pump was reinstalled, the mechanic adjusted the continuous flow fuel injection system using the airplane's JPI engine monitor system and an external low pressure gauge to set the takeoff fuel flow; he then refueled the plane from containers in which he had stored the fuel in order to service the fuel pump. The following day, the pilot and the mechanic again adjusted the fuel pump's fuel flow after conducting an unsatisfactory engine run-up . After the adjustment, the run-up appeared to be normal. Directives from the engine's manufacturer recommended using a Model 20 ATM-C Porta Test Unit or equivalent to ensure the fuel injection system meets all pressure and flow specifications. Using a JPI engine monitor and an external gauge would have given inaccurate results without a properly calibrated fuel pump, and the mechanic's recalibration of the engine-driven fuel pump's adjustment screw would have only masked the debris issue within the throttle assembly.

Further, review of the manufacturer's approved engine-out emergency procedures indicated that with a rear engine failure, the propeller should be immediately feathered and the landing gear retracted after obstacle clearance. Therefore, even with a loss of rear engine power, the airplane's operating manual indicated that the airplane would have been able to climb at least 275 feet per minute with one engine, assuming the required pilot inputs were made. Had those single-engine climb performance conditions been met, the airplane likely would have been able to, at a minimum, maintain altitude until a safe landing could have been accomplished. However, as the rear propeller was found with a low pitch angle and the landing gear was found in the down and locked position after the accident, the airplane had not been configured for maximum single-engine performance as outlined in the engine-out procedures.

Verbatim NTSB analysis and probable cause from the NTSB dataset