NTSB Identification: CHI87LA068.
The docket is stored on NTSB microfiche number 33593.
Accident occurred Monday, January 26, 1987 in MADISON, IN
Probable Cause Approval Date: 07/05/1988
Aircraft: CESSNA 172N, registration: N4688D
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

AT APRX 2500 MSL, THE ENG STOPPED AND ATTEMPTS TO RESTART IT WERE NOT SUCCESSFUL. THE INSTRUCTOR TOOK CONTROL OF THE ACFT AND ATTEMPTED TO LAND ON THE HIGHWAY, BUT THE ACFT STRUCK POWERLINES AND A TELEPHONE POLE BEFORE NOSING OVER AND COMING TO REST. THE ENG WAS REMOVED FROM THE ACFT AND SUBSEQUENT TEARDOWN REVEALED THAT THE CRANKSHAFT GEAR TEETH WERE SHEARED. APRX 140 HRS PRIOR TO THE ACCIDENT, A REPAIR STATION HAD RE-NITRIDED THE CRANKSHAFT FOLLOWING RE-GRINDING OPERATIONS, HOWEVER, THE PRESSED ON TYPE GEAR WAS NOT REMOVED, AS REQUIRED, PRIOR TO RE-NITRIDING. SPECIFICATIONS STATE THAT THE GEAR SHOULD HAVE A MIN ROCKWELL HARDNESS OF 30N-77 AND THAT ANY TEMP IN EXCESS OF 300 DEGREES F WOULD AFFECT THE HARDNESS. WHEN TESTED, THE GEAR EXHIBITED A ROCKWELL HARDNESS OF 30N-39. THE TEMP REQUIRED FOR NITRIDING IS IN EXCESS OF 985 DEGREES F.

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

ENGINE ASSEMBLY,CRANKSHAFT..FAILURE,PARTIAL

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

PROCEDURES/DIRECTIVES..NOT FOLLOWED..OTHER MAINTENANCE PERSONNEL

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

MAINTENANCE,INSTALLATION..IMPROPER..OTHER MAINTENANCE PERSONNEL

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

MAINTENANCE,MODIFICATION..IMPROPER..OTHER MAINTENANCE PERSONNEL



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