CEN23LA402

About 10 minutes into the accident flight, the pilot noticed the left and right battery indications on the instrument panel turned on and off several times. About 8 minutes later, he noticed a loss of electrical power to the secondary electronic flight instrument system (EFIS) and several other avionics, but the primary EFIS was still powered, and the engine continued to operate normally. The pilot turned back toward the departure airport and flew for another 10 minutes until the airplane lost all electrical and engine power. The pilot then made a forced landing to a field, which resulted in substantial damage to the airplane. Recorded flight data provided by the pilot indicated that the airplane’s EFIS generated a battery alert shortly before takeoff; intermittent battery alerts continued for about 17 minutes. However, the NTSB was unable to verify the accuracy of these data. Postaccident examinations revealed that the No. 2 alternator belt had failed; the No. 1 alternator belt remained intact. The airplane’s two batteries did not show any voltage when tested with a multimeter. Due to incorrect electrical wiring, only the No. 2 alternator charged the batteries while the airplane was operating. The No. 2 alternator belt likely failed in flight, after which the engine and some avionics were able to operate for a short time using battery power. Because the airplane was equipped with an electronic ignition and fuel injection system, the engine lost power when the batteries subsequently discharged and were unable to produce adequate voltage.

On September 4, 2023, about 1100 central daylight time, an RV-14A airplane, N14NP, was substantially damaged when it was involved in an accident near Orchard, Texas. The pilot and pilot-rated passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot had purchased the airplane from its builder about one month before the accident. According to the pilot, about 10 minutes into the accident flight from Fair Weather Field (TX42), Monaville, Texas, to Texas Gulf Coast Regional Airport (LBX), Angleton/Lake Jackson, Texas, he noticed the left and right battery indications on the instrument panel turned on and off several times. About 8 minutes later, he noticed a loss of electrical power to the secondary EFIS and several other avionics, but the primary EFIS was still powered, and the engine continued to operate normally. The pilot turned back toward TX42 and flew for another 10 minutes until the airplane lost all electrical and engine power. The pilot made a forced landing to a field and the airplane came to rest upright. Postaccident examination revealed that the airplane sustained substantial damage to the fuselage. The No. 2 alternator belt was broken. It was found inside the engine cowling, and the cowling had black rubber marks on its inside surface. The No. 1 alternator belt remained intact. During a subsequent examination, the two batteries did not show any voltage when tested with a multimeter. The two alternators were wired such that the No. 2 alternator was the only alternator charging the batteries. When tested, the No. 2 alternator worked as expected with no issues. The examination revealed no other mechanical malfunctions or anomalies that would have resulted in a loss of electrical or engine power. The airplane was equipped with an electronic ignition and injection system. The pilot stated that the alternator indication lights were not wired to turn on when the alternators are offline. The airplane builder told the pilot that he relied on the ammeters, which are displayed digitally on the EFIS, to show alternator functionality. The builder also told the pilot that the only indication that an alternator was working was when the needle pointed up on the corresponding ammeter. The pilot provided accident flight data to the NTSB that he said was recorded by the airplane’s EFIS. These data showed that a battery alert was first generated about 1031, when the airplane was traveling at a ground speed of about 3 knots. The recorded data showed an increase in ground speed about 20 seconds later, followed by an increase in altitude consistent with takeoff. Intermittent battery alerts continued until about 1048. The data also showed intermittent battery alerts during a 2-minute portion of an earlier flight on the same day. The airplane maintenance logbooks revealed that the airplane was equipped with two EarthX ETX900 13.2-volt lithium batteries, which had been installed by theairplane builder. On April 18, 2018, at airframe total time of 201.1 hours, he replaced the No. 2 alternator belt. The builder performed the airplane’s most recent annual condition inspection on February 1, 2023, about seven months before the accident, at airframe total time of 523.7 hours.