Event Sequence
On October 12, 2021, at about 1300 mountain daylight time, a Cessna 180, registration N926LL, was substantially damaged during a landing at an airport near Kalispell, Montana. The pilot, who was the sole occupant, was not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
According to the pilot, she initially received clearance to land on runway 20 but performed a go-around due to a tailwind. She then requested and was cleared to land on runway 02. Upon touchdown, the airplane abruptly veered right, skipped several times, and exited the right side of the runway, where the left wing contacted the terrain. The pilot stated that she was uncertain whether a mechanical malfunction or failure occurred.
A tower controller reported that the pilot had been cleared for runway 20 but went around after bouncing. The pilot then asked for runway 02, and after clearance, the airplane "skidded off east of runway mid-field."
Damage and Examination
The airplane came to rest upright in open terrain adjacent to the runway. The left wing and aileron exhibited a sharp upward bend from the tip to about 30 inches inboard. The right wing was bent downward, and the right strut buckled. The left horizontal stabilizer and elevator were bent upward at mid-span. The left main landing gear assembly separated from the fuselage. The landing gear had a wheel alignment shim on the left side but no shim on the right side. According to Cessna, wheel alignment shims are an "as required" item, and the absence of a shim is acceptable. The pre-accident wheel alignment could not be determined due to the left landing gear separation.
An FAA representative examined the accident site and reported that the damage pattern was consistent with a ground loop. The landing gear alignment could not be assessed because of the damage. No mechanical malfunctions or failures that would have precluded normal operation were found.
The airport's automated weather observation recorded wind from 040° at 4 knots with no gusts about the time of the accident.
Maintenance History
Five days before the accident, on October 7, 2021, maintenance was performed on N926LL. The main gear axle spindles were aligned, and new ABI-1010 wheels with 8.5-10 6-ply tires and tubes were installed per Supplemental Type Certificate (STC) SA017655E. New ABI 30-52N brake calipers were installed, and the left tailwheel cable was re-routed. The elevator and stabilizer movement were checked. The STC SA017655E addresses the installation of Alaskan Bushwheel TSO-C26d wheels (part number ABI-1010). Another STC, SA01015SE, covers the installation of eligible Alaska Tire and Rubber Company TSO-C62d tires. The FAA Approved Model Lists indicated that the Cessna 180H is approved for use with these components.
According to the mechanic who performed the work, the pilot's husband had reported handling problems during landings and requested different tires and rims. The mechanic replaced the tires, wheels, and brake calipers, setting the alignment per procedures for oversized tires.
The STC SA01015SE documentation includes a statement that tundra tires reduce directional stability and controllability during ground rolls, increase ground loop tendency, and increase nose-over tendency on paved surfaces relative to gravel or grass.