N7373Zlin Aviation S R O SAVAGE NORDEN · 2022

On August 30, 2023, about 1600 central daylight time, a Zlin Aviation Savage Norden airplane, N7373, was substantially damaged when it was involved in an accident near Cabot, Arkansas. The flight instructor and pilot receiving instruction were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight.

The flight instructor stated that they departed North Little Rock Municipal Airport (ORK), North Little Rock, Arkansas, and flew to Red Oak Airport (4AR2), Cabot, Arkansas, to perform takeoffs and landings for tailwheel training. Following an uneventful landing, they departed runway 09 at 4AR2 and remained in the traffic pattern. The flight instructor reported that, while on final approach, the engine sustained a total loss of power. He subsequently executed a forced landing to a field and the airplane impacted a fence during the landing roll. After the accident, he noticed a small fire in the engine compartment that continued for about 30 seconds.

Postaccident examination of the airplane revealed substantial damage to both wings and the fuselage. The engine remained attached to the airframe with minimal impact damage. Soot residue was observed on the right upper engine cowl air louvers, the engine valve covers, and the aft engine area. The throttle position sensor wiring, oil temperature sensor wiring, and the oil pressure sensor wiring were melted and damaged. The wiring for the two primary electric fuel pumps was thermally damaged and rested on the turbine section of the turbocharger and near the exhaust system. The fuel pumps would not function when tested with airframe controls. However, they functioned normally after the thermally damaged wires were bypassed.

The ECU data revealed that the engine parameters were nominal during the first portion of the flight and the throttle position corresponded to engine rpm as expected. During the final approach, the throttle position was reduced to 27%, which led to a corresponding decrease in engine speed to 1,844 rpm. About 7 seconds later, with the throttle position unchanged, the engine speed suddenly decreased to about 300 rpm, and the engine stopped running. The throttle position was then increased to 74% but the engine did not respond.

When the engine speed suddenly decreased to 300 rpm, the fuel injection mass and manifold pressure increased, consistent with the engine not receiving adequate fuel. The calculated fuel flow initially decreased as the engine's speed suddenly decreased to 300 rpm before it then increased rapidly, consistent with the ECM attempting to inject more fuel to compensate for the loss of engine speed.

During the initial loss of power, the ECU recorded two faults for Generator Select in Failsafe. According to Rotech, this fault can be caused by a lane check being conducted too quickly or by turning off the engine by switching off the fuel pumps (especially when the engine is running on Generator A). Rotech further reported that the Generator Select in Failsafe fault, “further substantiates the existence of fuel supply issues, as this fault was recorded at the time of the engine power loss.”

An exemplar airplane was examined; the fuel pump power wiring harness was routed near the firewall and not next to the turbocharger, as seen on the accident airplane. According to the airplane manufacturer’s sole U.S. distributor, there is currently no standardization for placement of the fuel pump wiring during the manufacturing process.