WPR23LA314

Factual narrative

On August 8, 2023, about 1824 mountain daylight time, an experimental amateur-built Team Acft Z-Max airplane, N440ZM, was substantially damaged when it was involved in an accident near Rigby, Idaho. The private pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot, who was also the airplane owner, reported that he had not flown the airplane in 8 years. The day before the accident flight, he drained and refilled the fuel tanks, cleaned the carburetors and fuel pump, and test ran the engine. He completed four taxi tests at Rigby Airport (U56) the day before and the day of the accident, before departing on the accident flight. The pilot does not remember the accident flight. A witness reported the pilot told him that he had been working on the engine because he was having problems getting it to start. On the day before and the day of the accident flight, the pilot was working on the engine and was seen taxiing the airplane up and down the taxiway. Shortly after, the witness saw the airplane depart on the accident flight. The witness stated the airplane flew past his hangar about 100-200 ft above ground level (agl) heading southbound. As the airplane passed his hangar, he heard the engine sputtering and it was not operating at full power. He remembers the airplane making an abrupt left turn above the airport, and while in the turn, the left wing dropped sharply. The airplane then descended and impacted the ground with the left wing. Examination of the accident site revealed that the airplane impacted the taxiway and came to rest in the runway safety area, on the east side of the airport. The header fuel tank separated from the airplane during the accident sequence and was burned. The fuselage and wings sustained substantial damage and did not catch fire. Postaccident examination of the wreckage revealed that two red wires from the starter solenoid to the voltage regulator were inadequately secured and worn on their outer sheath, revealing the internal copper wires. The wires were routed across the right forward side of the engine support structure. The copper wires were in contact with the metal support structure. Figure 1- Wire routing. Figure 2- Wire sheath worn. The airplane’s maintenance records were not available during the investigation. FAA Advisory Circular 43.13-1B Section 8, paragraph 11-96, “Wiring Installation Inspection Requirements,” states that wires and cables should be inspected for adequacy of support, protection, and general condition throughout. Ensure that wires and cables are routed in such a manner that chafing will not occur against the airframe or other components. Before takeoff for a local flight, the pilot emptied the wing tanks, cleaned the carburetors and fuel pump, and test ran the engine. The airplane had not flown in 8 years. A witness saw the airplane taxi up and down the taxiway multiple times both the day before and day of the accident, and then saw it depart on the accident flight. The witness heard the engine sputtering shortly after takeoff and stated that it was not operating at full power. The witness recalled the airplane made an abrupt left turn above the airport, and while in the turn, the left wing dropped sharply. The airplane then descended and impacted the ground with the left wing. Postaccident examination of the wreckage revealed that two wires from the starter solenoid to the voltage regulator were inadequately secured and worn on their outer sheath, revealing the internal copper wires. The wires were routed across the right forward side of the engine support structure. The copper wires were in contact with the support structure, which likely grounded the airplane’s electrical system and caused the engine to lose power. The sudden drop of the left wing during the turn was consistent with the pilot exceeding the airplane’s critical angle of attack during the turn, resulting in an aerodynamic stall at an altitude too low for recovery. Source: NTSB Aviation Accident Database Retrieved: 2026-02-12

NTSB Findings

FAA avdata. C = Cause, F = Factor.

• — Aircraft-Aircraft power plant-Engine (reciprocating)-Recip eng wiring-Fatigue/wear/corrosion
• — Aircraft-Aircraft power plant-Engine (reciprocating)-Recip eng wiring-Failure
• — Aircraft-Aircraft power plant-Engine (reciprocating)-Recip eng wiring-Incorrect service/maintenance
• — Personnel issues-Task performance-Use of equip/info-Aircraft control-Pilot
• — Aircraft-Aircraft oper/perf/capability-Performance/control parameters-(general)-Not attained/maintained