Hi Jim, Hi Tinker,
Thanks for all your thought provoking input and research.
You might remember I’m the OP (original poster), so although I apparently don’t have either of your depth of detail of the regs, I am the one who flew the perimeter in iFly (both Sectional and Vector) while exchanging position data with the tower (re distance from perimeter), and had two talks with the tower, one with the manager, so from that status, I’ll put in a few more cents:
Jim, you wrote, in part ---
“My point about the controlling ATC facility reporting an error...it just seems to me that if I'm a tower controller at XYZ airport, I would quickly know if the depicted class D is incorrect. Why are all these airplanes flying in my class D without calling me? How hard would it be to look at a sectional a couple times a year to see if the depiction is correct?”
And you wrote “would be totally unacceptable to have an airspace system full of ambiguity. I don't think it is. This has got to be an unusual situation IMHO.”
Is this as you say “an unusual situation?” I certainly hope so. I’d be willing to bet it is unusual. But that doesn’t mean it isn’t the actual situation.
It seems unequivocal to me that the tower staff I dealt with at MFR was and is consciously using 5nm radius as their perimeter while iFly was showing it as darn close to 5 statute miles (4.3nm) and Tinker’s research reveals it as 4.1nm. I can’t see any other interpretation of these facts other that to conclude that, as unlikely as it seems, the tower staff would have their own airspace wrong, is that is indeed the case.
In conversation with one controller he said (this is a paraphrase, not a quote) “Yeah, I’ve been puzzled for a long time about why pilots would fly so close to our airspace”
My guess about what’s been going on is prudent pilots wanting to not incur have, for example, been clearing the actual 4.1nm perimeter by, say, about one nm and being “seen” by the controller to be barely clearing at ~5.1nm . Rather than as you suggest ATC interpreting that as “hey, maybe we need to look at a sectional to see if we’ve got a incorrect understanding of our airspace“, IMO (and per my talk with ATC) the more plausible interpretation at ATC is along the lines of “we’ve got a few pilots out there who don’t have the sense to allow a little slack around airspace.”
Why should a controller question what the other controllers told him/her their airspace was when he started working there? “It’s 5nm”. If I started working there that would’ve sounded reasonable to me. No reason to research it. As Tinker suggests in what I quote from him below, it’s easy to see how this becomes the tribal belief so “obvious“ that in the event of any anomaly you‘d look for any explanation other than questioning the obvious. ;-) And it’s not like this 0.9 disparity/error is causing major issues. Most exchanges with pilots, unlike my experiments with them, aren’t along the lines of “I’m 1 mile from your perimeter” but “I’m 10 miles out over table rock” (or whatever.) There would be no disparities in those exchanges between me and the tower or the tower and my iFly.
To add a bit to how this looks to a controller, when I phoned another class D, Klamath Falls, and asked a controller “is your perimeter 5 statute miles or 5 nautical” he said “hang on a minute, I’ll ask” then came back on with “5 statute miles … 4.3 nautical.” Point being he apparently works all day with what he sees on screen as his perimeter but didn’t even know off the top of his head (and didn’t really need to know) exactly what the official number is…. Just whether targets are inside or outside, and whether there are potential conflicts.
Tinker, you wrote in part --
"And, remember, the OPs issue now appears to be that the MFR controllers do not know the size of their own airspace. That seems odd, but my friend the tower manager had to dig to find that JO. He had been told during training what his tower airspace diameter was and he had passed that along to his trainees. Sort of an oral tradition and folklore process that in his case did not lead them astray. Possibly at MFR the same process led to the wrong tribal belief. I hope the OP will point the MFR guys to the JO and will report back on their reaction. It would be interesting to hear.”
I’m a bit reluctant to be calling up ATC and be seen as telling them I know their turf better than they do. Might not be appreciated, especially coming from a 350 hour pilot. (There’s the “shoot the messenger” risk.) Have to fly here often don’t want to be the bad guy.) But may do so despite that, as it would be good to get it straightened out; as at least eliminating a .9nm disparity in the perimeter between ATC and pilots’ GPS ‘s should remove some minor annoyance and confusion, and at best could save someone from an accident someday. But I’d want to have the exact reference to send them too. Guess I could do it with “can you help me out…. I’m confused about what I’m reading here.
So, pardon my ignorance but what’s the “JO” I need to refer to and/or have with me? If I’m going phone in or sit down with, or email, the tower manager what would suggest I have at hand?
Can you save me some footwork (as you’re way ahead of me on that) and give me or send me to those resources?
Alex