NTSB Identification: CHI91DCD01.
The docket is stored on NTSB microfiche number 44706.
Accident occurred Sunday, June 23, 1991 in DAVENPORT, IA
Probable Cause Approval Date: 07/29/1992
Aircraft: HEAL SONERAI-I, registration: N4227N
Injuries: 1 Fatal.

THE PLT WAS PARTICIPATING IN A PYLON AIR RACE FOR FORMULA V RACERS. ABT HALF WAY THRU THE RACE, AS HE WAS MNVRG PAST THE #2 PYLON, THE LEFT WING BGN TO SEPARATE. THE WING THEN FOLDED OVR THE TOP OF THE ACFT. THE WING & PIECES OF THE CANOPY FELL TO THE GND. AS THE WING SEPD, THE ACFT BGN A VIOLENT ROLL & FLWD A TRAJECTORY PATH TO THE GND. INV REVEALED THE INNER PORTION OF EACH WING WAS DESIGNED WITH BOX SPAR CONSTRUCTION, SECURED TO A FUSELAGE CARRY-THRU CONFIGURATION. THE OUTER WING SPARS CONSISTED OF A SERIES OF UPPER & LOWER STRAPS. THESE WERE SECURED TO A SHEET METAL WEB WITH RIVETS. THE 4 LOWER SPAR STRAPS HAD FAILED; 2 HAD FAILED AT THE 1ST RIVET HOLE OUTBOARD OF THE BOX SPAR CONFIGURATION; ONE FAILED AT THE 1ST BOLT HOLE NEAR THE OUTBOARD END OF THE BOX SPAR & THE 4TH FAILED FLUSH WITH THE OUTBOARD END OF THE BOX SPAR.

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

FAILURE OF THE WING SPAR STRAPS, AS THE AIRCRAFT WAS BEING MANEUVERED AROUND A PYLON IN AN AIR RACE.

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