Found this
i]First and foremost, I'd like to remind everyone that the FAA put out a
FDC NOTAM 12 years ago requiring all pilots flying anywhere in the USA
to monitor 121.5. This was promulgated as an FDC NOTAM rather than a
regulation, but unlike the advisory L/D-NOTAMs, which are merely
inform you of certain conditions, FDC NOTAMs have regulatory force.
The one involved is FDC 4/4386, which says in part, "ALL AIRCRAFT
OPERATING IN UNITED STATES NATIONAL AIRSPACE, IF CAPABLE, SHALL
MAINTAIN A LISTENING WATCH ON VHF GUARD
121.5 OR UHF 243.0." I'd like to emphasize that when the FAA says
"shall", that term "is used in an imperative sense", meaning you have
no choice about doing it.
ASquared. Do I get an correction?