Accident Overview
On August 30, 2023, at approximately 1600 central daylight time, a Zlin Aviation Savage Norden airplane, registration N7373, was substantially damaged during an accident near Cabot, Arkansas. The flight, conducted under Title 14 Code of Federal Regulations Part 91 as an instructional flight, involved a flight instructor and a pilot receiving instruction. Both individuals were not injured.
Flight Details
The flight departed from North Little Rock Municipal Airport (ORK) in North Little Rock, Arkansas, and proceeded to Red Oak Airport (4AR2) in Cabot, Arkansas, for tailwheel training takeoffs and landings. After an uneventful landing, the airplane departed runway 09 at 4AR2 and remained in the traffic pattern. While on final approach, the engine experienced a total loss of power. The flight instructor executed a forced landing to a field, and during the landing roll, the airplane impacted a fence. Following the accident, a small fire was observed in the engine compartment that persisted for about 30 seconds.
Damage Examination
Postaccident examination revealed substantial damage to both wings and the fuselage. The engine remained attached to the airframe with minimal impact damage. Soot residue was present on the right upper engine cowl air louvers, engine valve covers, and the aft engine area. The throttle position sensor wiring, oil temperature sensor wiring, and 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 did not function when tested with airframe controls but operated normally after the thermally damaged wires were bypassed.
ECU Data Analysis
Engine control unit (ECU) data showed that engine parameters were nominal during the first portion of the flight, with throttle position corresponding to engine rpm as expected. During the final approach, the throttle was reduced to 27%, leading to a decrease in engine speed to 1,844 rpm. About 7 seconds later, with the throttle unchanged, engine speed suddenly dropped to approximately 300 rpm, and the engine stopped running. The throttle was then increased to 74%, but the engine did not respond.
When engine speed decreased to 300 rpm, fuel injection mass and manifold pressure increased, consistent with inadequate fuel delivery. Calculated fuel flow initially decreased as engine speed dropped, then increased rapidly, indicating that the engine control module attempted to inject more fuel to compensate for the loss of speed.
ECU Faults
During the initial power loss, the ECU recorded two faults for "Generator Select in Failsafe." According to Rotech, this fault can occur if a lane check is performed too quickly or if the engine is turned off by switching off the fuel pumps, particularly 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."
Wiring Routing Observations
An exemplar airplane was examined, and its fuel pump power wiring harness was routed near the firewall, not adjacent 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 the placement of the fuel pump wiring during the manufacturing process.