Page 4-8 G3X Installation Manual – GSU 73Revision A 190-01115-014.8 MaintenancePer Part 43 Appendix E, paragraph (b)(2), Garmin specifies a test procedure equivalent to part 43Appendix E, paragraph (b)(1) with two exceptions. The tests of sub-paragraph (iv)(Friction) and (vi)(Barometric Scale Error) are not applicable because the digital outputs of the GSU 73 are not susceptibleto these types of errors.A GSU 73 Field Calibration Tool (not yet available) can be used to adjust the calibration of GSU 73 unitsthat have failed the 14 CFR Part 43 Appendix E tests due to altitude drift.The GSU 73 utilizes an Earth magnetic field model which is updated once every five years. This IGRF(International Geomagnetic Reference Field) update is expected to be available from Garmin by July 1 ofeach of the following years: 2010, 2015, and every five years thereafter, so long as the GSU 73 remains aGarmin –supported product. The IGRF model can be updated by the end user via the internet, it is notnecessary to return the GSU 73 to Garmin for this update. Otherwise maintenance of the GSU 73 is ‘oncondition’ only.
