AD 2022-03-15 Prompted By A Report Of A Fuel Quantity Disparity

The FAA is adopting a new airworthiness directive (AD) for various airplanes modified with certain configurations of Garmin G3X Touch Electronic Flight Instrument System installed per Supplemental Type Certificate (STC) No. SA01899WI or Garmin GI 275 Multi-Function Display (MFD) installed per STC No. SA02658SE.

This AD was prompted by a report of a fuel quantity disparity between the amount of fuel indicated and the actual amount of fuel. This AD requires modifying the resistive fuel probe interface. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective March 21, 2022.

Supplementary Information: The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to various airplanes modified with certain configurations of Garmin G3X Touch Electronic Flight Instrument System installed per STC No. SA01899WI or Garmin GI 275 MFD installed per STC No. SA02658SE. The NPRM published in the Federal Register on August 27, 2021 (86 FR 48070). The NPRM was prompted by notification of a Piper production line issue with the installation of a Garmin G3X Touch Electronic Flight Instrument System installed under STC No. SA01899WI. After calibration and fueling the airplane to a known level, the flight crew noted that the fuel quantity indicator displayed a higher level of fuel.

The Garmin G3X Touch Electronic Flight Instrument System, when interfaced with the Garmin GEA 24 (Engine Airframe Adapter) for display of the fuel quantity, uses a 1K ohm resistor inline between the GEA 24 and the airplane fuel quantity resistance style sending unit (float). This resistor provides lightning protection to the fuel tank as required by 14 CFR 23.954.

Use of the 1K resistor causes a GEA error when the GEA 24 or resistor is subjected to significantly hotter or colder temperatures than the temperature at which the fuel gauges were calibrated during installation. The farther the actual (ambient) temperature of the GEA 24 or resistor is from the temperature of the fuel quantity calibration, the larger the error. The lower the operating resistance of the fuel sending unit, the larger the error. The largest errors occur in installations with fuel sending units having an operational range less than 100 ohms. The Garmin GI 275 MFDs installed under STC No. SA02658SE, when interfaced with the Garmin GEA 24 for display of the fuel quantity, is also subject to this unsafe condition.

The displayed fuel quantity can have an error as much as four gallons/fuel tank with the display indicating four gallons with an empty tank. In the NPRM, the FAA proposed to require modifying the resistive fuel probe interface. The FAA is issuing this AD to prevent fuel starvation and engine shutdown, which could result in the inability to arrive at the destination airport or a suitable alternative airport.

FMI: www.regulations.gov