Amateur-built SQ-12 N37PX accident near Palmer, Alaska

Probable cause

The fuel injector manufacturer's inappropriate guidance to use a 5-ampere circuit breaker in place of the required 10-ampere circuit breaker on the fuel injector circuit, which resulted in the circuit breaker opening, a loss of electrical power to the electronic fuel injectors, and a subsequent total loss of engine power.

NTSB analysis

The private pilot reported that, while in level cruise flight, the engine experienced a total loss of power; he then made a forced landing to a remote gravel bar. During the forced landing, the airplane sustained substantial damage to the left lift strut and fuselage. Following the forced landing, the pilot noticed that the 5-ampere fuel injector circuit breaker had opened.

A postaccident engine run at various idle power settings revealed no evidence of any preimpact mechanical anomalies with the airplane's engine or systems.

The airplane was equipped with an EFII electronic fuel injection and ignition system. A postaccident examination of the system revealed that the fuel injectors had been separated from the ignition power circuit and installed on their own dedicated circuit. The circuit was protected with one 5-ampere circuit breaker, with each individual fuel injector requiring up to 1.25 ampere of electrical current. The EFII installation manual requires one 10-ampere circuit breaker for the ignition circuit, which includes power leads for the ignition coil packs and the electronic fuel injectors. The company that installed the EFII harness provided correspondence from a previous EFII electronic fuel injection and ignition installation, where EFII had recommended that a 5-ampere circuit breaker be used if the fuel injectors were placed on their own dedicated circuit. The installation company stated that this guidance was applied to the accident airplane's installation.

Because the 5-ampere circuit breaker was installed, it is likely that the circuit breaker opened and resulted in a loss of electrical power to the electronic fuel injectors, which then resulted in a total loss of engine power.

Text from the NTSB. Open the NTSB docket for ANC17LA008 for the full record.