FAR 91.215(c) allows that a transponder may be turned off in limited areas outside of controlled airspace.
However, 91.225(f) states “each person operating an aircraft equipped with ADS-B Out must operate this equipment in the transmit mode at all times.”
This means that while ADS-B Out may not be required in certain airspace until 2020, those who have already equipped must keep it turned on in all airspace.
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