Amateur-built STOL CH 750 N484XB accident near Grain Valley, Missouri

Probable cause

The pilot’s failure to maintain airplane control during a low-speed, high-pitch climb after the airplane experienced a loss of electrical power and subsequent total loss of engine power, which resulted in an aerodynamic stall. Contributing to the accident was the airplane’s modified electrical system and the pilot’s failure to obtain adequate familiarization and experience in the airplane with the recent slat-removed configuration.

NTSB analysis

Data from the onboard avionics device revealed that, after conducting a touch-and-go landing, the amateur-built airplane immediately began a low-speed, high-pitch-angle climb. The airplane's airspeed began to decrease as the airplane climbed to about 47 ft above ground level and then began rolling left; the recording then ended. Witnesses reported observing the airplane roll, descend, and impact terrain. The data and the witness statements are consistent with the airplane having experienced an aerodynamic stall. A postaccident examination of the composite propeller found that it did not display signatures of rotation during impact, consistent with a total loss of engine power.

The engine manufacturer's initial installation used a single battery with a series of breakers and relays to provide power to the engine components and other equipment. This design was subsequently replaced by a dual-battery design that incorporated a simpler wiring harness. The airplane was originally wired for a single-battery operation, and a second battery was subsequently added. However, the simpler wiring harness was not used; instead the electrical path from the alternator to the alternator sense wire used a complex series of fuses to provide power to the components; one of these fuses was found open, which is indicative of an electrical power failure and would have led to the loss of engine power. Although the onboard avionics device did not record the airplane's loss of engine power, descent, or impact with terrain, the interruption of the recorded data likely resulted from the electrical failure.

The pilot had removed the airplane's slats 9 days before the accident; the accident flight was the pilot's first flight in the airplane with the new configuration. According to the kit designer, the airplane was not designed to fly with the slats removed because it would result in a higher stall speed with a distinct stall break and roll if the flight was not coordinated. In addition, the pilot had recently resumed flying after not having flown in about 45 years. Although he had received 2 hours of dual instruction about 2 months before the accident, after a test flight in a company airplane, another pilot assessed the accident pilot's piloting skills as poor and advised him to obtain further instruction; however, the accident pilot did not do so. Given his lack of recent flight experience, he was likely not properly prepared for how to respond to a loss of engine power and the subsequent stall.

Text from the NTSB. Open the NTSB docket for CEN14LA441 for the full record.