On April 24, 1990, a Bellanca 8KCAB (registration N2976R) operated by Gran-aire, Inc. was involved in an aviation accident near West Bend, WI. Investigators recorded the probable cause as: The right wing separated due to fatigue progression in both side plates of the lift strut-to-wing spar attachment fitting, with initiation areas adjacent to the ends of two welds. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
The right wing separated from an aircraft during an instructional aerobatic flight. Metallurgical examination found fatigue progression in both side plates of the lift strut-to-wing spar attachment fitting, initiating adjacent to weld ends.
Accident Details
During an instructional aerobatic flight, the right wing separated from the aircraft. The aircraft was engaged in aerobatic maneuvers at the time of the event.
Metallurgical Examination
A metallurgical examination of the separated wing revealed that the lift strut-to-wing spar attachment fitting had failed. The failure was due to fatigue progression in both side plates of the fitting. The initiation areas of the fatigue cracks were located immediately adjacent to the ends of two welds on the fitting.
In the weld heat-affected zone, the microstructure transitioned from a spheroidized pearlite region near the base metal into a coarse tempered martensite region adjacent to the fusion zone. This microstructural variation indicates a change in material properties across the weld region, consistent with the observed fatigue initiation sites.
Probable cause
The right wing separated due to fatigue progression in both side plates of the lift strut-to-wing spar attachment fitting, with initiation areas adjacent to the ends of two welds.
What happened in the 24 Apr 1990 Bellanca 8KCAB accident near West Bend, WI?
The right wing separated from an aircraft during an instructional aerobatic flight. Metallurgical examination found fatigue progression in both side plates of the lift strut-to-wing spar attachment fitting, initiating adjacent to weld ends.
What aircraft was involved and where did it happen?
The accident on 24 Apr 1990 involved a Bellanca 8KCAB, registration N2976R, operated by Gran-aire, Inc., at West Bend, WI.
What was the probable cause of the accident?
The right wing separated due to fatigue progression in both side plates of the lift strut-to-wing spar attachment fitting, with initiation areas adjacent to the ends of two welds.
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