100 N225CK accident near Glendale, Arizona

Probable cause

Maintenance personnel’s failure to comply with the procedures of an airworthiness directive, which resulted in a fatigue failure of the longitudinal frame tube during landing and collapse of the right main landing gear.

NTSB analysis

The pilot and pilot-rated passenger took turns performing touch-and-go maneuvers. According to their recount, the landings were smooth, and they did not observe or hear anything unusual. After their final touchdown, which was also normal, they heard a thud, and the airplane veered to the right. The pilot attempted to correct the movement but was unsuccessful. The airplane departed the right runway edge, the right main landing gear collapsed, and the airplane came to rest.

Examination of the airplane revealed that the right main landing gear strut had failed due to preexisting upward crushing deformation of the longitudinal frame tube where it mated with the upper clamp at the outboard right main landing gear location. The longitudinal frame tube was likely crushed during a prior landing, which reduced the clamping force on the gear leg. Witness marks and rubbed surfaces on the longitudinal frame tube and upper clamp surfaces and a fatigue fracture on the inboard attachment bolt suggest that the looseness that resulted from the crushed tube had existed for some time before the accident. Further, the fatigue cracks that led to the fracture of the inboard attachment bolt likely developed due to looseness at the outboard attachment location.

The airplane manufacturer released an alert service bulletin (ASB) requiring an inspection of the longitudinal frame tube for cracks at 50-hour intervals and to measure the tube’s wall thickness. The ASB was followed-up by a Federal Aviation Administration airworthiness directive (AD) that referred to the procedures established within the ASB. Entries in the accident airplane’s logbook indicated that the main landing gear had been inspected in accordance with the AD. However, the mechanic who performed the inspection did not comply with the procedures prescribed by the ASB, despite it being a requirement specifically listed in the AD. This required a reinforcement of the frame tube and would have prevented the landing gear failure; however, no repair was ever made.

Text from the NTSB. Open the NTSB docket for WPR20LA165 for the full record.