190-01115-01
G3X/G3X Touch Installation Manual - Maintenance
Rev. AC
Page 36-2
36.1.3 GSU 73
Per Part 43 Appendix E, paragraph (b)(2), Garmin recommends a test procedure equivalent to part 43
Appendix 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 susceptible to
these types of errors. This procedure is recommended when the static system is opened up (i.e. whenever
the GSU 73 is removed or replaced). Garmin also recommends that a leak test be performed following any
maintenance action in which the pitot pneumatic line is opened up (i.e. whenever the GSU 73 is removed
or replaced).
A GSU 73 Field Calibration Tool can be used to adjust the calibration of GSU 73 units that have failed the
14 CFR Part 43 Appendix E tests due to altitude drift. Please contact a local Garmin dealer for more
information.
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 in July of
2020 and every five years thereafter, so long as the GSU 73 remains a Garmin –supported product. The
IGRF model is automatically updated with a GDU software update. Alternatively, the IGRF model can be
updated by the end user via the Garmin website (
www.garmin.com
), it is not necessary to return the GSU
73 to Garmin for this update. Otherwise maintenance of the GSU 73 is ‘on condition’ only.
