On March 10, 1984, a Cessna 421B (registration N41022) was involved in an aviation accident near Madison, WI. Investigators recorded the probable cause as: The pilot's inability to maintain directional control during landing due to overload failures of the bellcrank assembly bolts, which sheared off without signs of fatigue. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During a landing with strong crosswinds, the aircraft departed the runway to the left. Post-accident inspection revealed that overload failures of the bellcrank assembly bolts caused the loss of control.
What happened
The aircraft departed the runway surface to the left side while executing a landing maneuver. At the time of the incident, wind conditions were characterized by a crosswind component ranging between 15 and 28 knots. The pilot reported that the aircraft began to veer to the left during the roll-out phase and was unable to be maintained on the runway centerline.
The investigation
Following the accident, a mechanical inspection was conducted to determine the condition of the flight control linkages. Examination revealed that specific hardware components had failed. Specifically, the 464P-26 bolt and the 5133-4032 spacer were found to be sheared off from both the left and right bellcrank assemblies.
Findings
A qualified mechanic analyzed the failed components and determined that the bolts experienced overload failures. The inspection showed no evidence of fatigue in the metal, indicating that the failure was sudden and caused by excessive force rather than material wear or age. The loss of control was directly attributed to these mechanical failures during the critical landing phase.
Probable cause
The pilot's inability to maintain directional control during landing due to overload failures of the bellcrank assembly bolts, which sheared off without signs of fatigue.