CEN25LA401

Shortly into the local area flight with the experimental amateur-built airplane, the pilot noticed a flicker on the avionics display, but a low voltage warning never appeared. The pilot then looked at the engine monitoring display which indicated the alternator was not charging, and it showed 12.8 volts direct current (VDC) on the main battery. The pilot immediately started a climbing turn back to the departure airport. After reaching about 4,000 ft, he tried several methods to get the alternator working including cycling both the field and the main alternator circuit breakers several times. He checked the voltage for the ignition backup battery, which read 12.8 VDC. Since he had about a 15-minute flight back to the departure airport, he decided to save the ignition backup battery and run off the main battery until he received a low voltage warning. The airplane was on final approach when a low voltage warning appeared on the display. The pilot switched over to the ignition backup battery and watched as the voltage dropped from 12.8 VDC down to 0 VDC, and the engine sustained a total loss of engine power. The pilot reported that the ignition backup battery only lasted about one or two minutes before the voltage dropped to 0 VDC. While on short final, about 300 ft agl, the pilot performed a forced landing near trees and a grass field. The airplane came to rest nose down in the trees and sustained substantial damage to both wings and the wing struts. Postaccident engine examination revealed a fractured ring terminal for the 12-volt alternator. It is likely that the ring terminal fractured from vibrations while the engine was operating. It is also likely that there was too much tension and not enough relief on the wire that the ring terminal was connected during the installation to the alternator. The airplane’s engine was built to use a dual electronic ignition system that operated from the airplane’s electrical system, which included the main battery, the alternator to maintain the main battery’s charge, and the ignition backup battery. Once the ring terminal fractured, the ignition system relied completely on the main battery as the source of ignition power. Once the main battery power was depleted and the ignition backup battery power was depleted, the ignition system could not operate, and the engine sustained a total loss of power due to the lack of ignition. The airplane did not accumulate enough time to require its first annual inspection for the airframe and the engine. According to the airplane maintenance manual, the ignition backup battery is to be changed at each annual inspection. The pilot expressed concern that with the ignition backup battery that came with the kit, as it may take a builder some time to complete the building of the airplane, and that could easily go over a one-year timeline for example. The pilot would not have been able to detect the fractured ring terminal without removing the engine cowl, which is not normallypart of the pilot’s preflight inspection.

On September 7, 2025, about 0932 eastern daylight time, a CubCrafters CCK-2000 EX airplane, N40DT, sustained substantial damage when it was involved in an accident near Thompsonville, Michigan. The private pilot and the passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The experimental airplane, known as a Carbon Cub, which the pilot built from a kit, departed from the Thompsonville Airport (7Y2), Thompsonville, Michigan, about 0917. Shortly into the local area flight, the pilot noticed a flicker on the Garmin G3X Touch display, but a low voltage warning never appeared. The pilot then looked at the engine monitoring display which indicated the alternator was not charging and it showed 12.8 volts direct current (VDC) on the main battery. The pilot immediately started a climbing turn back to 7Y2. After reaching about 4,000 ft, he tried several methods to get the alternator working including cycling both the field and the main alternator circuit breakers several times. He checked the voltage for the ignition backup battery, which read 12.8 VDC. Since he had about a 15-minute flight back to 7Y2, he decided to save the ignition backup battery and run off the main battery until he received a low voltage warning. The airplane was on final approach when a low voltage warning appeared on the Garmin G3X Touch display. The pilot switched over to the ignition backup battery, he watched as the voltage dropped from 12.8 VDC down to 0 VDC, and the engine sustained a total loss of engine power. The pilot noticed that the ignition backup battery was faulty, and it only lasted about one or two minutes. While on short final, about 300 ft agl, the pilot performed a forced landing near trees and a grass field. During the forced landing, the airplane came to rest nose down in the trees. The pilot and the passenger were able to egress from the airplane. The airplane sustained substantial damage to both wings and the wing struts. Postaccident examination of the engine revealed a fractured ring terminal for the Denso 021080-0760 12-volt alternator. The ring terminal, a 10 AWG (American Wire Guage), was found fractured in place. The pilot reported that the fractured ring terminal is from a harness, which does not have a part number, came with the kit he purchased (see figure 1). Figure 1 – View of the fractured ring terminal in the red circle (courtesy of the pilot). The pilot reported that the ring terminal likely fractured from vibrations while the engine was operating and that it is possible that there might have been too much tension on the wire and ring terminal. The pilot additionally reported that he did not have any previous issues with the alternator, including during the build process. The engine was built to use a dual electronic ignition system that operated from the airplane’s electrical system, which included the main battery, the alternator to maintain the main battery’s charge, and theignition backup battery. The engine, which was equipped with a dual electronic ignition system (Light Speed Engineering 1.334-D-H-22 Dual Plasma III), does not have magnetos installed. The 12-volt ignition backup battery that failed, a Power Sonic PS-1221S (that has a CubCrafters part number of SP91001-201), had a decal on it that stated “received 03/14/2023.” The ignition backup battery also came with the kit that he purchased and was installed during the build process. A review of the historical FAA airworthiness records showed that a conformity inspection was performed by an FAA aviation safety inspector on the airplane on July 7, 2025, and that a FAA special airworthiness certificate was issued for the airplane on the same date. The airplane did not accumulate enough time to require its first annual inspection for the airframe and the engine. According to the CubCrafters CCK-2000 airplane maintenance manual, the ignition backup battery is to be changed at each annual inspection. The pilot expressed concern with the ignition backup battery that came with the kit, as it may take a builder some time to complete the building of the airplane, and that could easily go over a one-year timeline. The pilot reported he believed the ignition backup battery failed because it was old. For the Garmin G3X Touch display, the pilot reported the following voltage settings were programed from the airplane: 10.0-10.8 Volts – Red Range + Alert 10.8-11.5 Volts – Yellow Range + Alert 11.5-12.6 Volts – Yellow Range 12.6-15.8 Volts – Green Range 15.0-15.8 Volts – Yellow Range + Alert 15.8-16.0 Volts – Red Range + Alert For the area where the ring terminal fractured by the alternator, it is not visible during a preflight inspection to a pilot, as the engine cowl covers it.