NTSB Identification: SEA05LA153.
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Accident occurred Thursday, July 28, 2005 in Sunriver, OR
Probable Cause Approval Date: 03/28/2006
Aircraft: Mooney M20J, registration: N110MP
Injuries: 3 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.

According to the pilot, while on the downwind leg for landing on runway 18, the engine "backfired, ran rough and quit." During the ensuing forced landing, the airplane collided with trees and terrain short of the runway. The left outer wing sustained structural damage. During an attempted engine run following the accident, the engine could not be started, and it was determined that both sets of magneto points were not opening. Inspection of the single-drive dual magneto found that the nylon cam followers on both sets of points were worn to the point that they could no longer open the contacts. The cam followers appeared to be burned and discolored due to a lack of lubrication. The felt pads mounted on the cam followers that are normally saturated with lubricating oil were found to be very dry. The magneto manufacturer's recommended maintenance instructions call for the cam follower felt pads to be inspected for the presence of adequate lubricating oil every 100 hours time in service. According to the airplane's maintenance records the points had accumulated 372.9 hours since installation on January 1, 2001. There were no entries found in the engine logbook indicating the points had been inspected since their installation.

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

The loss of engine power as a result of both sets of magneto points failing to open due to excessive wear of the nylon cam followers. The excessive wear of the cam followers was due to maintenance personnel's failure to follow the magneto manufacturer's recommended maintenance procedures and inspect the cam follower felt pads for adequate lubrication at 100-hour intervals. A factor was the lack of suitable terrain available for the forced landing.

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