Thor
Switching off the TANS makes the screen go blank. It is pointless then doing a Waypoint change. When you switch off your TV you don,t try to change channels or adjust volume. Same principle.
Robin
Just what does the TANS Power Switch control?
It certainly has no effect on the GM Compass. You can continue to use that.
It certainly has no effect on the raw doppler. Separate power switch, control panel and display.
I am pretty certain the ADC just works once power is supplied. It is on throughout the flight.
Trimble GPS?
If the TANS power switch was Switched Off by the crew some 26 secs before impact, and this did also switch off the Trimble GPS:
Then the final position recorded in the TANS should be 170 G/S x26 secs down track from the actual impact position. That is 1.4nms or 8500ft.
No such error is recorded.