The FAA has proposed an airworthiness directive (AD) calling for the modification of a component of some Garmin G3X Touch electronic flight instrument system installations following the detection of a disparity between the amount of fuel displayed and the actual quantity of fuel aboard an aircraft.
The proposed AD would require modifying the resistive fuel probe interface of about 920 aircraft on the approved model list for Supplemental Type Certificate “No. SA01899WI, installed in accordance with MDL Document No. 005-01320-00, Revision 9 or earlier, and STC No. SA02658SE, installed in accordance with MDL Drawing No. 005-01208-41, Revision 9 or earlier, if the installation is interfaced with a Garmin Engine Adapter GEA 24 connected to resistive fuel probes.”
According to the AD, “the FAA was notified 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.”
When interfaced as the AD describes, the Garmin G3X Touch “uses a 1K ohm resistor inline between the GEA 24 and the airplane fuel quantity resistance style sending unit,” for lightning protection of the fuel tank.
“The farther the actual (ambient) temperature of the resistor is from the temperature of the fuel quantity calibration, the larger the error,” the AD says, noting that the system “can have an error as much as four gallons/fuel tank with the display indicating four gallons with an empty tank.”
The FAA estimated the cost to modify the fuel probe interface and recalibrate the fuel system at $690 per aircraft.
Comments on the proposed AD may be submitted by October 12 online or by mail to U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590. Please include “Docket No. FAA-2021-0715; Project Identifier AD-2021-00259-A” at the beginning of your comments.