NTSB Identification: CHI90FA233.
The docket is stored on NTSB microfiche number 42783.
Accident occurred Thursday, August 16, 1990 in ODELL, IL
Probable Cause Approval Date: 12/14/1992
Aircraft: PIPER PA-23-160, registration: N4231P
Injuries: 3 Uninjured.

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.

DURING FLIGHT THE LEFT ENGINE BEGAN RUNNING ROUGH AND VIBRATING SEVERELY, AND IT WAS SHUT DOWN. THE PILOT WAS UNABLE TO MAINTAIN ALTITUDE ON THE RIGHT ENGINE AND A FORCED LANDING WAS MADE IN AN ALFALFA FIELD. EXAMINATION REVEALED THAT THE LEFT ENGINES RIGHT MAGNETO HAD AN ACCUMULATION OF OIL INSIDE ITS CASE. IN ADDITION, THE SPARK PLUG LEAD FROM THE LEFT MAGNETO FOR THE #1 CYLINDER WAS INTERNALLY DAMAGED. EXAMINATION OF THE RIGHT ENGINE REVEALED THAT THE INTAKE DUCT BETWEEN THE AIR FILTER AND THE CARBURETOR WAS DETERIORATED FROM EXPOSURE TO HOT EXHAUST PIPES. A 3' X 1/2' PIECE OF THE DUCT HAD SEPARATED AND WAS FOUND CAUGHT ON THE CARBURETOR VENTURI.

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

A LOSS OF LEFT ENGINE POWER DUE TO OIL ACCUMULATION IN THE RIGHT MAGNETO AND A NON-USABLE SPARK LEAD FROM THE LEFT MAGNETO. IN ADDITION, THE RIGHT ENGINE WAS UNABLE TO PROVIDE ADEQUATE POWER TO MAINTAIN ALTITUDE DUE TO A PARTIAL BLOCKAGE IN THE CARBURETOR BY A SECTION OF AIR INTAKE DUCT WHICH CAUSED THE ENGINE TO RUN RICH.

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