On November 4, 2023, at 1200 Pacific standard time, an Arrow Falcon Exporters UH-1H, N3053Q, was substantially damaged during startup near Firebaugh, California. The pilot was not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight. The pilot stated that he thought the helicopter may not have been flown for the prior 2 weeks. He performed the preflight inspection and startup with no anomalies. As he was turning on the GPS system and putting his helmet on, he began to see and smell smoke in the cockpit. He looked outside and noted smoke coming from the upper engine compartment, so he secured and shut down the helicopter and called 911. The fire department extinguished the fire. Postaccident examination of the helicopter revealed significant thermal damage to the left side cockpit and cargo areas near the engine from the on-ground fire. The engine remained attached to the upper engine compartment. The engine side fuel filter remained in its normal position with the fuel lines attached. The area where the fuel shutoff valve was located on the airframe side was thermally destroyed and the fuel lines were thermally consumed in the fire. Maintenance personnel concluded the fire started on the airframe side at a fuel inlet line to the fuel shutoff valve. A review of the maintenance logbooks showed an annual inspection had been completed on July 18, 2023, about three and a half months before the accident. According to the director of maintenance, the fuel line fittings would have been checked for tightness at that time.