AIRBORNE EXTREME LLC SQ-12

Full Narrative

On November 25, 2016, about 1330 Alaska standard time, a tailwheel-equipped Airborne Extreme LLC SQ12 airplane, N37PX, sustained substantial damage during a forced landing, following a loss of engine power near Palmer, Alaska. The airplane was registered to Airborne Extreme LLC and operated by the pilot as a visual flight rules flight under the provisions of 14 Code of Federal Regulations Part 91 when the accident occurred. The certificated private pilot and two passengers were not injured. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight departed Jackfish Landing Airport (7AK4), Wasilla, Alaska at about 1250.

During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on November 25, the pilot reported that the he had departed for an afternoon flight with two family members up the Knik Glacier. About 40 minutes after departure, while in level cruise flight the engine lost all power. He 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.

In the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1) submitted by the pilot, he indicated that following the forced landing he noticed that the 5-ampere fuel injector circuit breaker had popped.

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, while still mounted on the accident airplane's airframe was operated under the direction of the NTSB IIC, along with the rest of the investigative team. The engine was not run at full power due to impact damage to the airframe and propeller sustained during the accident, but it was operated at various idle power settings while cycling through both engine control units (ECU) 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 which was protect with one 5-ampere circuit breaker. In addition, one 10-ampere circuit breaker supplied power to each individual ignition coil pack.

A review of the EFII installation manual indicates that one 10-ampere circuit breaker is required for the ignition power circuit on 4 cylinder engines. The single 10-ampere circuit breaker supplies 12-volt power to the two ignition coil packs and all four electronic fuel injectors. In addition, all wiring harnesses shipped by EFII have power wires bundled with a heat shrink label on them with the appropriate breaker requirement.

According to EFII, the most electrical current required by each individual fuel injector is about 1.25-ampere, with the potential for a 75% duty cycle.

In an email provided to the NTSB IIC, Aerotronics, Inc. stated that prior to working on the accident airplane, they installed an EFII electronic fuel injection and ignition system on another airplane. That airplane owner had requested that the fuel injectors be separated from the ignition harness. The owner had contacted EFII and requested guidance on what size breaker would be appropriate for a dedicated fuel injector circuit. EFII responded in an email "If there is going to be a separate breaker for the injector power, I would make it 5A." (A copy of this email, along with comments from EFII regarding the provided guidance is available in the public docket for this accident.) Aerotronics also stated that they followed that guidance provided by EFII on both the previous installation and on the accident airplane installation.

The closest weather reporting facility was Palmer Municipal Airport, Palmer, Alaska, about 30 miles northwest of the accident site. At 1353, an Aviation Routine Weather Report (METAR) from Palmer Airport was reporting, in part: wind from 120 degrees at 3 knots; visibility, 10 statute miles; clouds and sky condition, few clouds at 7,000 feet, scattered clouds at 12,000 feet; temperature, 10 degrees F; dew point 9 degrees F; altimeter, 29.21 inHG.

ADDITIONAL INFORMATION

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 would not only protect the ignition circuit, but would provide additional protection for each individual fuel injector. Additionally, this design would reduce the possibility of an electrical short on one fuel injector resulting in an open circuit, and a loss of power to all fuel injectors, and a subsequent total loss of engine power.