NTSB Identification: CHI07LA159.
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Accident occurred Wednesday, May 30, 2007 in Middleton, WI
Probable Cause Approval Date: 04/30/2008
Aircraft: Cessna 340A, registration: N17MH
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot stated that multiple approaches and landings had been conducted during the dual proficiency flight. Prior to the accident landing, he observed three green lights indicating that the landing gear was properly extended. The landing touchdown was "light." A "few seconds" after touchdown the aircraft began to "shudder" and the gear horn started to sound. The airplane began to drift right and the right wing began to settle. As the right main gear collapsed, the aircraft departed the runway pavement, striking two runway lights in the process. The aircraft came to rest in a grass area adjacent to the runway. The nose and left main landing gear remained extended during the accident. A post accident examination of the aircraft revealed that the forward bellcrank attachment flange on the landing gear strut failed. In addition, the lower flange on the bellcrank had also failed. According to the airplane manufacturer, the location of the failures was consistent with the cumulative effect of improper adjustment of the downlock mechanism over time. However, any improper adjustment procedure could not be attributed to any specific maintenance action or to a particular mechanic. Additionally, the maintenance log entry related to the adjustments made during the most recent annual inspection indicated that the airplane maintenance manual instructions regarding landing gear adjustments were complied with properly.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

Failure of the right main landing gear extension and retraction linkage, which allowed the gear assembly to collapse during landing rollout. An additional cause was the improper adjustment procedure(s) by undetermined mechanic(s). The runway lights struck during the accident sequence were contributing factors.

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