NTSB Identification: FTW89FA107.
The docket is stored on NTSB microfiche number 40526.
Accident occurred Friday, June 02, 1989 in HENRYETTA, OK
Probable Cause Approval Date: 09/30/1991
Aircraft: PITTS S-1S, registration: N64652
Injuries: 3 Serious,2 Minor.

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.

POWER LOSS OCCURRED DUE TO SEPARATION AND DEPARTURE OF LOWER 1/2 RT EXHAUST STACK. PLT MADE A FORCED LANDING ON THE 2 NORTHBOUND LANES OF A DIVIDED HWY. ON SHORT FINAL, THE ACFT STRUCK POWER LINES, CRASHED, AND SLID INTO A TRUCK TRAVELLING NORTH. A PASSENGER CAR, TRAVELLING SOUTH, BECAME ENTANGLED IN THE WIRES AND WAS SUBSEQUENTLY REAR ENDED BY ANOTHER BEHICLE. THE POWER LINE POLES WERE MASKED FROM VIEW BY TREES ON BOTH SIDES OF THE ROAD. EXAMINATION OF THE EXHAUST STACK REVEALED THAT IT HAD UNDERGONE EXTENSIVE POST-MANUFACTURE REPAIRS IN THE AREA OF THE SEPARATION. THERE WAS EVIDENCE OF EXTENSIVE WELD FUSION ZONE POROSITY IN THE AREA THAT HAD BEEN WELDED. WELD FUSION ZONE POROSITY HAS BEEN ATTRIBUTED IN THE PAST TO POOR SURFACE PREPARATION AND WELD REPAIR TECHNIQUES.

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

AN ENGINE POWER LOSS DUE TO THE SEPARATION AND DEPARTURE OF AN EXHAUST STACK. THE STACK FAILED DUE TO POOR WELD. FACTOR(S) WAS: THE TERRAIN CONDITIONS OF THE SELECTED FORCED LANDING SITE.

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