What does this Caution box on the sectional chart near Half Moon Bay, California mean? Is there an official reference for the meaning of this box?
This one is a bit confusing and interestingly there is nothing in the FAA's sectional guide on "Caution" boxes although they do appear on other charts as well.
This one in particular is a warning that you will need monitor the radio for the transition routes below 2000 ft. If you can zoom in or get TAC level map resolution you will see a different warning
If you note a bit south of half moon bay the chart makes note of the fact you should be using the TAC in that area:
1$\begingroup$ I already +1ed, but then noted the contact frequency is different than the 124.3. This thread suggests it's a <2000 CTAF. $\endgroup$– user14897Jan 24, 2020 at 12:56
$\begingroup$ I don't think the answer is correct. Below 4,000-6,000 you are outside class B and you don't need ATC - it is a VFR Flyway. The VFR Transition Route is above 4,000-6,000. $\endgroup$– rvernicaJan 25, 2020 at 22:30
$\begingroup$ @rvernica I read that as the flyway being "Below 6000 or Below 4000" depending on where you are, not above. $\endgroup$– DaveJan 25, 2020 at 23:28
$\begingroup$ @Dave that is correct, the flyway is below and ATC clearance is not required on the flyway. $\endgroup$– rvernicaJan 26, 2020 at 0:10
$\begingroup$ @rvernica is it just a monitor the frequency situation? Ill update the answer to be a bit more vague $\endgroup$– DaveJan 26, 2020 at 0:36