Yakovlev YAK 52 N132MD accident near Porterville, California

Probable cause

A partial loss of engine power due to contaminants in the fuel system that decreased the fuel flow, the source of which could not be determined.

NTSB analysis

The airline transport pilot reported that, during a formation flight, the engine started to run rough. Unable to maintain level flight, the pilot detached from the formation to troubleshoot the problem. The pilot noted that there were about 29 gallons of useable fuel onboard and all other indications were normal. The engine continued to lose power, and about 500 ft above the ground, the pilot elected to land in a vineyard. During landing, the airplane touched down, came to an abrupt stop, nosed over, and came to rest inverted.

Postaccident engine examination revealed small pieces of fabric in the fuel screen. In addition, some metal shavings and a small piece of metal were found in the fuel intake and carburetor inlet screen. The origins of the metal piece and shavings could not be determined. It is unlikely that the observed debris was enough to clog the fuel system; however, it is possible that there were other, non-observable pieces of debris in the fuel system that could have resulted in decreased fuel flow and the partial loss of engine power.

Text from the NTSB. Open the NTSB docket for WPR17LA094 for the full record.