iFly GPS Forum

Even though my experience of engaging with the controllers there and even the manager was completely cooperative in tone from their and my end.... I would be a bit leary of being viewed as the messenger coming to tell them they`re wrong and I know their business better than they do. ;-)
Last thing I want is to get on the wrong side of these folks who I depend on for critical cooperation and support when I`m in the air.
I might raise it with them at the right time and place.

There`s still the interesting and potentially important question of how many or how few other ATCs out there have made a similar slip up. With similar potential for unexpected incursions from pilots using the shown GPS perimiter? It`s easy to see how that (the manager at a tower thinking of nautical miles instead of statute miles when setting up to monitor and control their airspace) could happen...... as ALL other transactions (reports of position to and from aircraft) are ALL done in nautical miles.

So I repeat my request:
Anyone hear willing to call any control towers and ask them if they monitor their perimeter as X nautical miles or X statute miles (5 for Class D, 10 for Class C, etc.)?

Alex

I just now decided to try to answer my own last-posted question, which was something like "are other ATC's mistakely using a 5 (10, or whatever) nautical mile radius as their perimeter when they're shown on FAA docs (Sectional, TAC, etc) and pilot's GPS as 5 statute miles.

So far I reached only one other (not that easy to get direct-to-control-tower phone numbers):

Klamath Falls class-D KLMT told me, as expected/hoped by-the-book, their radius is 5 statute miles, and as an aside mention that's 4.35 nautical miles.

I'll see if I can collect enough of these to make a statement about how common or rare it might be for ATC to be overreaching their airspace when believing an aircraft has entered.

I believe it's worth investigating how common this nautical-mile/statute-mile confounding of perimeter by ATC might be. If a class-C ATC were to incorectly monitor their airspace as 30 nautical miles when officially it is 30 statute miles the potential for problems would be even greater than near class-D: My iFly would be showing me a full 4 nautical miles outside their airspace .... which I'd probably view as a comfortable margin ... right at the moment ATC would be seeing me entering their airspace with neither having made radio contact nor having the required transponder. In a situation such as that, if it exists, the rule of thumb we've all agreed on here (essentially, cut yourself a mile or two of slack if you want to communicate with ATC, or just want to avoid an airspace) would be insufficient margin.

Alex