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Via the ATSB report -
The aircraft was fitted with two Garmin 128 marine-type GPS units that provided aircraft tracking and groundspeed information...
...The absence of recorded tracking data in the last minutes of flight was consistent with previously-recorded approaches, including to Brewarrina Airport that day. Ground testing of the GPS unit could only replicate this phenomenon if the power supply to the GPS unit was turned off prior to reaching the destination.
It was therefore possible that, for a short time during the final approach segment, the pilot’s attention was diverted to the task of selecting the GPS unit OFF. The investigation could not establish the extent to which that selection, if made, might have affected the pilot’s ability to maintain a safe profile during the final approach segment for runway 19...
Why was the pilot turning off the GPS ?
Apparently this is a garmin 128 (with three levels of back lighting) -
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