Originally Posted by
Gonzo
To my knowledge PANS ATM does not mandate the inclusion of the unit being used in the RTF message.......
See the above, and:
DOC 9432 - 3.1.3:
"The following words may be omitted from transmissions provided that
no confusion or ambiguity will result:
d) “HECTOPASCALS” when giving pressure settings."
I think that should settle it.
So in my opinion, since US pilots have a nasty tendency of abbreviating pressure settings, putting "hectopascal" after the QNH when below 1000, is meeting the requirement in DOC 9432, when handling US registrered aircraft, or in doubt.