NTSB Identification: ATL89FA163.
The docket is stored on NTSB microfiche number 40956.
Accident occurred Saturday, June 17, 1989 in VERNON, AL
Probable Cause Approval Date: 06/22/1992
Aircraft: CESSNA 172F, registration: N7939U
Injuries: 1 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.

WITNESSES OBSERVED THE ACFT AT ABOUT 100 FT AGL WITH THE ENGINE SPUTTERING, MISSING. IT THEN CRASHED INVERTED IN A LARGE OPEN FIELD ABOUT 100 FT EAST OF A LINE OF TREES; ONE TREE HAD SEVERAL BRANCHES BROKEN NEAR THE TOP. ENG TEST/TEARDOWN REVEALED NO COMPRESSION #6 CYL; BOTTOM SPARK PLUG CENTER ELECTRODE MISSING; ELECTRODE DEBRIS IN EXHAUST VALVE SEAT/FACE. THE FAILED PLUG SHOWED EVIDENCE OF EXCESSIVE OPERATING TEMPERATURES AND PREIGNITION. LAST ANNUAL WAS 11/3/83, ABOUT 44 HRS PRIOR TO ACCIDENT. ALL PLUGS APPEARED TO HAVE BEEN RECENTLY CLEANED AND SERVICED; NONE OF THE REMAINING PLUGS EXHIBITED EVIDENCE OF DETONATION OR PREIGNITION. PILOT PERFORMED OWN MAINTENANCE AND ALSO REPORTEDLY MIXED OWN AUTO/AVIATION GASOLINE.

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

IMPROPER MAINTENANCE OF THE SPARK PLUGS BY THE PILOT/MECHANIC WHICH RESULTED IN A PARTIAL LOSS OF ENGINE POWER, AND THE PILOT'S FAILURE TO CLEAR TREES DURING AN EMERGENCY LANDING IN AN OPEN FIELD RESULTING IN AN INADVERTENT STALL.

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