Accident Details
On November 25, 2016, at about 1330 Alaska standard time, a tailwheel-equipped Airborne Extreme LLC SQ12 airplane, registration N37PX, sustained substantial damage during a forced landing after a loss of engine power near Palmer, Alaska. The airplane was operated by the pilot under 14 CFR Part 91 as a visual flight rules flight. The certificated private pilot and two passengers were not injured. Visual meteorological conditions prevailed, and no flight plan was filed. The flight departed Jackfish Landing Airport (7AK4), Wasilla, Alaska, at about 1250.
The pilot reported that after departing for an afternoon flight with two family members up the Knik Glacier, about 40 minutes into the flight, while in level cruise, the engine lost all power. He executed a forced landing to a remote gravel bar, during which the airplane sustained substantial damage to the left lift strut and fuselage.
In the submitted accident report, the pilot indicated that after the forced landing, he noticed the 5-ampere fuel injector circuit breaker had popped.
Investigation Findings
The airplane was equipped with a 4-cylinder Titan 409 angle valve series engine and an EFII electronic fuel injection and ignition system.
On December 12, 2016, the engine, still mounted on the airframe, was operated under the direction of the NTSB investigator-in-charge. Due to impact damage, the engine was not run at full power but was operated at various idle power settings while cycling through both engine control units and fuel pumps. No anomalies were observed.
Further investigation revealed that the fuel injectors had been separated from the ignition power circuit and installed on their own dedicated circuit, protected by a 5-ampere circuit breaker. Additionally, a 10-ampere circuit breaker supplied power to each individual ignition coil pack.
A review of the EFII installation manual indicated that a single 10-ampere circuit breaker is required for the ignition power circuit on 4-cylinder engines, supplying power to the two ignition coil packs and all four electronic fuel injectors. Wiring harnesses shipped by EFII have power wires bundled with a heat shrink label indicating the appropriate breaker requirement. According to EFII, each fuel injector requires about 1.25 amperes maximum, with a potential 75% duty cycle.
In an email to the NTSB, Aerotronics, Inc. stated that prior to working on the accident airplane, they installed an EFII system on another airplane where the owner requested separation of injectors from the ignition harness. That owner contacted EFII for guidance on the appropriate breaker size for a dedicated injector circuit, and EFII responded, "If there is going to be a separate breaker for the injector power, I would make it 5A." Aerotronics followed that guidance on both installations.
Weather
The closest weather reporting facility was Palmer Municipal Airport, about 30 miles northwest of the accident site. At 1353, a METAR reported wind from 120 degrees at 3 knots, visibility 10 statute miles, few clouds at 7,000 feet, scattered clouds at 12,000 feet, temperature 10°F, dew point 9°F, and altimeter 29.21 inHg.
Post-Accident Changes
Following this accident, EFII began evaluating injector power setups with integral 7.5-ampere fusible links on each injector feed, in addition to the 10-ampere required circuit breaker. This design aims to protect the ignition circuit and provide additional protection for each injector, reducing the possibility of an electrical short on one injector causing a loss of power to all injectors and subsequent total engine power loss.