I think it’s worth quoting a few more of the ENR paras, one of which Checkboard quoted:
9.1.7 In the vicinity of uncharted aerodromes, pilots have discretion to use the most appropriate frequency that ensures safe operation. This may be 126.7MHz. However, pilots should be aware that transiting aircraft will be monitoring Area VHF. To ensure mutual traffic awareness, it is recommended that pilots using an alternative frequency also monitor Area VHF.
9.1.8 It is required (unless operating in accordance with procedures in the Part 103 MOS) that gliders operating above 5,000FT in Class G airspace monitor the Area VHF.
9.1.9 An aircraft is considered in the vicinity of a non-controlled aerodrome if it is within 10NM of the aerodrome and at a height above the aerodrome that could result in conflict with operations at the aerodrome.
9.1.7 is yet another idea on the spectrum of ideas about the ‘appropriate’ frequency to be used at uncharted aerodromes. Remember when the debate raged about whether it should be 126.7 or Area? So now the answer from the brains trust seems to be: You pick!
More importantly, so far as my question about the altitude/height parameter to ‘trigger’ the ‘vicinity’ change to CTAF is concerned, I note the quoted bits use (apparently) altitude for the requirement for gliders to monitor Area - above 5,000’ - but height for the general provision about ‘vicinity’.
Is an aircraft overflying YCOM west to east at 5,500’ supposed to switch to and broadcast ‘overflying’ on, then monitor, YCOM CTAF at or before 10nms onwards? I would have thought yes, because the aircraft will overly YCOM at a height of only 2,400’. But the gliders at 5,500’ within 10nms of YCOM are on Area.
So: What is the “height above the aerodrome that could result in conflict with operations at the aerodrome”? Isn’t it axiomatic that if we all have different answers to that question, there’s a ‘safety’ issue?
And it’s why I’m still interested in understanding what parameters a gizmo would use to do the frequency change automatically.