Originally Posted by
wigglyamp
Incidentally, the fail flag does more than just indicate a satisfactory received signal and unit power. If the converter detects loss of either VOR 30Hz signal (reference phase or variable phase) it will also drop the flag. Similarly in LOC mode, if either the 90Hz or 150Hz signals of the ILS are missing, the flag should also appear, otherwise the CDI could indicate full deviation based on just one side of the ILS beam being received.
Thanks for the info, I learned something new....gotta love pprune....ask an obscure technical question and in a little while an expert will arrive and provide an explanation
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However there are still failure modes where the unit will provide erroneous nav information with no flag in view. My only point was to not blindly accept what you are seeing on the instrument just because no flags are in view.