N40DT

On September 7, 2025, about 0932 eastern daylight time, a CubCrafters Carbon Cub EX airplane, N40DT, sustained substantial damage when it was involved in an accident near Thompsonville, Michigan. The private pilot was not injured and the passenger sustained minor injury. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 personal flight.

The airplane 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). 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 main alternator circuit breakers several times. He checked the voltage in the backup ignition battery which read 12.8 VDC.

Since he had about a 15-minute flight back to 7Y2, he decided to save the backup ignition 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 backup ignition 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 backup battery was faulty, and it only lasted about one or two minutes.

While on short final, about 300 ft, the pilot performed a forced landing near trees. During the forced landing, the airplane came to rest nose down in the trees. The airplane sustained substantial damage to both wings and the wing struts.

The wreckage was recovered from the accident site to 7Y2. Postaccident examination of the engine revealed a broken ring terminal for the Denso 021080-0760 12-volt alternator. The pilot reported the broken ring terminal is from a factory-built harness (see figure 1).

Figure 1 – View of the broken ring terminal in the red circle (courtesy of the pilot).

The pilot built the experimental airplane from a kit in 2025. The airplane was equipped with a CubCrafters CC363i (Lycoming Engines YIO-360-EXP128) reciprocating engine. The airplane was also equipped with a two-blade carbon fiber composite Hartzell Propeller HC-C2YR-IN/NG8301 Trailblazer Homebuilt constant speed propeller.