Originally Posted by
CaptainMidnight
I don't know about the history of the introduction of this "U" inside a circle symbol, but I assume that after the fuss in 2015 re deleting ALAs for which data could not be verified, someone in Airservices decided it was a way to placate the industry. What if any consultation was done I don't know, but it seems their charting people may not have been alerted to update the legends. Then of course in 2016 Airservices VRed or IVRed a few hundred of their "back room" people and a lot of knowledge (particularly historical) and expertise went out the door.
FWIW ICAO Annex 4 Aero charts Appendix 2 has basic recommended symbology:
Then para 2.4.1 says:
So perhaps that's what the FAA and Airservices have hung their hats on to offer additional symbols.
Useful stuff (as usual) CM.
It seems to me that the FAA has stuck with the ICAO symbology of a single unbroken circle, but just added stuff inside (or the curious “Objectionable”).
The provenance of the broken circle on Australia’s charts remains a mystery. And, given that the legend of the Australian chart says a broken circle denotes that the place is unverified, the point of adding the ‘U’ remains a bigger mystery.