NTSB Identification: SEA89FA099.
The docket is stored on NTSB microfiche number 40978.
Accident occurred Sunday, June 04, 1989 in MANSFIELD, WA
Probable Cause Approval Date: 06/26/1992
Aircraft: CUSHING 4, registration: N5321U
Injuries: 2 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

THE LEFT WING OF THE HOMEBUILT SEPARATED IN FLIGHT. THE WING MAIN SPAR WAS A HEAVY WOODEN BEAM WITH METAL REINFORCEMENT PLATES BOLTED TO THE FORE AND AFT SURFACES THAT EXTENDED THROUGH THE AIRCRAFT CABIN. THE SPAR WAS FOUND BROKEN ADJACENT TO THE LEFT SIDE OF THE CABIN, THROUGH BOLT HOLES AT THE METAL REINFORCEMENT BRACKETS. THE WOOD SPLINTERS IN THE FRACTURED SPAR WERE BENT TOWARD THE TOP SURFACE OF THE WING. THERE WAS NO EVIDENCE OF FATIGUE CRACKING OR DRY ROTTING.

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

FAILURE OF THE LEFT WING MAIN SPAR DUE TO OVERLOAD FOR UNDETERMINED REASONS.

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