Zlin Aviation S R O SAVAGE NORDEN N7373 accident near Cabot, Arkansas

Probable cause

The airplane manufacturer’s routing of the fuel pump wiring next to the engine’s turbocharger and exhaust, which thermally damaged the wiring and resulted in a malfunction of the fuel delivery system and a total loss of engine power.

NTSB analysis

The flight instructor and pilot receiving instruction, who was also the airplane owner, were performing takeoffs and landings as part of a tailwheel training flight. After an uneventful landing, they departed, remained in the traffic pattern, and were on final approach when the engine lost all power. The flight instructor took control of the airplane and conducted a forced landing to a field. The airplane impacted a fence and sustained substantial damage to both wings and the fuselage. The flight instructor noticed a small fire in the engine compartment after the accident that continued for about 30 seconds.

Postaccident examination revealed that the wiring for the 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. Examination of the remaining systems revealed no mechanical anomalies that would have precluded normal operations.

The engine control unit (ECU) data confirmed that the engine functioned normally for the majority of the flight but exhibited a total loss of power during the final approach. The data illustrated that the pilot increased the throttle position but the engine did not respond.

Examination of an exemplar airplane revealed that the fuel pump’s wiring harness was routed near the firewall and not next to the turbocharger and exhaust, as observed 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. It is most likely that the engine lost power due to the thermally-damaged fuel pump wiring.

Text from the NTSB. Open the NTSB docket for CEN23LA390 for the full record.