Amateur-built Kitfox N87TJ accident near Nampa, Idaho

Probable cause

The owner's improper installation of the tailwheel, which resulted in the pilot's inability to maintain directional control during landing as a result of severe tailwheel vibrations.

NTSB analysis

The pilot reported that, during takeoff in the experimental, amateur-built, tailwheel-equipped airplane, he experienced a hard shimmy before liftoff. Following an uneventful flight, the pilot landed the airplane onto the main landing gear. When the tailwheel touched down, the airplane immediately became uncontrollable and unresponsive. The airplane was rolling toward the right side of the runway and the pilot applied the brakes in an attempt to slow the airplane. The propeller contacted the runway surface before the airplane exited the runway, nosed over, and came to rest inverted.

The pilot reported that, about 6 to 8 weeks before the accident, the owner installed a larger tailwheel on the airplane. The original tailwheel was about 3 or 4 inches in diameter. The new tailwheel was about 6 inches in diameter.

A postaccident examination of the airplane revealed that the airplane was equipped with a 1 1/4-inch tailwheel leaf spring. The new tailwheel was designed for a 1 1/2-inch tailwheel leaf spring; therefore, a shim would have been required to ensure proper installation. In addition, a longer bolt would be needed to ensure that the bolt would properly secure within the locking nut. The examination revealed that the bolt was still present in the leaf spring, but the locking nut was not present and was not located along the runway. The washer was found underneath the tail, and there were no indications that a shim was installed. The bolt was removed from the leaf spring and measured; it was not long enough to reach the locking portion of the locking nut.

Since the bolt was not long enough to reach the locking portion of the locking nut, it is likely that the nut vibrated loose during normal operations, which caused excessive play in the tailwheel during landing.

Text from the NTSB. Open the NTSB docket for WPR19TA248 for the full record.