Cessna 180A N5281D accident near Nordman, Idaho

Probable cause

Maintenance personnel's improper installation of the left main landing gear wheel assembly, which resulted in a loss of torque and subsequent separation of the wheel and axle assembly from the main landing gear leg during landing.

NTSB analysis

The pilot reported he was receiving flight instruction and was practicing landings in a tailwheel-equipped airplane. During a power-off approach, the throttle was set to idle and carburetor heat was applied. As the airplane approached short final, both pilots observed an increased sink rate and the flight instructor called for additional power. Although power was increased, the engine briefly hesitated before full power was requested again. The flight instructor adjusted pitch and power, which resulted in a firm touchdown with a minimal bounce. Upon touchdown, the left wheel and axle assembly separated from the left main landing gear leg. The landing gear leg struck the grass surface and the left main landing gear leg fractured at the fuselage end. The airplane slid on the left wing and right main landing gear wheel before it came to rest 180° opposite the direction of landing.

Post accident examination of the airplane revealed that the left main landing gear axle assembly had separated; the landing gear attachment bolts remained in place, however, the attachment nuts were not present. Following a search of the accident area, the nuts were not recovered.

Metallurgical examination of the fractured landing gear leg revealed features consistent with inboard bending overstress. Although the separation occurred after the wheel and axle assembly detached, the fracture surface exhibited a fatigue crack that had originated from a corrosion pit on the outboard surface of the leg which had been painted over.

The corrosion pitting indicated that either the corrosion was not observed or ignored during the last overhaul or landing gear exchange when the floats were removed and the airplane wheels reinstalled.

Improper maintenance of the attachment bolts during assembly on the left main landing gear axle likely left them loosely secure, which produced inadequate thread engagement; unable to sustain the stress of landing loads, the bolts failed, which caused the wheel assembly to separate during the landing roll.

Text from the NTSB. Open the NTSB docket for WPR24LA122 for the full record.