Amateur-built S21 N46JH accident near Fairfield, Utah

Probable cause

The owner’s (pilot) failure to properly torque a fuel filter b-nut fitting, which likely introduced air into the fuel system and resulted in a loss of engine power. Contributing to the loss of power was a missing restricted bypass line and a header tank vent line, which would have allowed the venting of air from the fuel system.

NTSB analysis

The pilot was conducting a test flight following recent maintenance when, shortly after departing, the engine began to lose power. He performed a forced landing on airport property, during which the airplane landed hard and sustained substantial damage.

Postaccident examination of the engine revealed that the fuel filter b-nut fitting was not properly torqued, which likely introduced air into the fuel system. Additionally, there was no restricted bypass line between the inlet (pressure side of the fuel pump module) and the return line and no vent line from the header tank, both of which would have allowed the venting of air from the fuel system. Based on this evidence, it is likely that the loose fuel filter b-nut allowed the air into the fuel system that could not be properly vented due to the lack of a restricted bypass line and vent line, which ultimately resulted in the loss of engine power.

Text from the NTSB. Open the NTSB docket for WPR22LA211 for the full record.