ATC and iFly disparity in location? - iFly General Discussions

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ATC and iFly disparity in location?

6/13/2014 2:48 PM

ComputerDoc

Joined: 4/1/2012

Posts: 269

Re: ATC and iFly disparity in location? Modified By ComputerDoc on 6/13/2014 2:53:35 PM

Tinker wrote IN PART:

I know a couple of people at FAA-ATC ..... I just emailed them suggesting that possibly some FAA QC guy would be interested in this, maybe to the point of joining/commenting on the thread. I'll let you know if I hear anything.

Thanks. Be great to hear from them.

My suggestion/hope would if they do anything, rather than slapping anyone's hands or singling out my local ATC, it might just result in them generating an official reminder to all ATCs along these lines:

"it has come to our attention that some controllers are mistakenly using an integral number nautical miles as their airspace radius when their airspace is an integral number of statute miles. This can and has resulted in, incidents of disparities between pilots being outside airspace but appearing to ATC to be inside.airspaces For example, most class-D have a 5 statute mile radius, not 5 nautical miles. Determine if this misunderstanding could be occuring at your facility, and if so correct it."

Alex

6/17/2014 10:50 AM

Tinker

Joined: 2/9/2014

Posts: 109

Re: ATC and iFly disparity in location?

Not sure where to put this, but I'll add it here rather than to the new thread.

I got a call this morning from the local tower manager, a guy I know fairly well. He is also a CFII. I had sent my inquiry to one of his bosses up the line and the inquiry got bucked down to him. He found the discussion here to be somewhat interesting and had done some homework in the subject. We talked for maybe 15 minutes. Things learned:

All tower airspace is defined (individually for each tower) in FAA Job Order 7400.9X. (http://www.faa.gov/regulations_policies/orders_notices/index.cfm/go/document.information/documentID/1022106) In that order, the airspaces are defined in nautical miles (definitions, 1002, page A-2) unless otherwise stated. A search for "statute miles" produced three or four hits (it's a 1500 page document!) in some airway definitions. Nothing in the tower airspace definitions. In other words, all tower airspace is defined in nautical miles.

Our local Delta radius is a little under 4 miles, but they keep a 5 mile ring displayed on their D-Brite 'scope because the FAFs for the instrument approaches are at about 5 miles thus making the 5 mile ring a better reference for them. He also commented that none of his guys would even bother to tell him if an airplane slightly clipped their Delta without getting permission. They will also issue traffic advisories to known aircraft whether the aircraft is technically inside the delta or not.

He suggested this rule of thumb: "When the FAA talks miles, it is nautical miles unless it has to do with visibility."

I am too lazy to dig through the posts and look up the airports mentioned, but if someone does this I think all will be revealed.

6/20/2014 7:19 PM

Tinker

Joined: 2/9/2014

Posts: 109

Re: ATC and iFly disparity in location?

For those who may not be following the "deux" thread, it appears that the disparity mystery is solved:

***********************************************
ANM OR D Medford, OR
Rogue Valley International-Medford Airport, OR
(lat. 42°22'20"N, long. 122°52'21"W.)

That airspace extending upward from the surface to and including 3,800 feet MSL within a
4.1-mile radius of Rogue Valley International-Medford Airport. This Class D airspace area is
effective during the specific dates and times established in advance by a Notice to Airmen.
The effective date and time will thereafter be continuously published in the Airport/
Facility Directory.

AMENDMENTS 10/3/02 67 FR 51070 (Revised)
***********************************************

So the the JO says the the Medford Delta is 4.1NM, not the 5NM that the tower told the OP that it is using. 4.1NM is 4.71SM, pretty close to the 5SM that the OP said he measured on the sectional.

6/26/2014 7:53 PM

ComputerDoc

Joined: 4/1/2012

Posts: 269

Re: ATC and iFly disparity in location?

Here`s how it finally resolved (this post is by Alex, the OP):

Per earlier posts we pretty much came down to this when I last posted:

#MFR airspace actually has officially a 4.1 nm radius.

#The iFly sectional is/was accurately reporting the perimeter in flight at 4.1nm.

#Controllers at the tower were operating under a mistaken impression that the radius was 5nm. Resulting in minor, but annoying, misunderstandings of when aircraft were incurring on the airspace, etc.

I emailed the FAA office that accepts reports of discrepancies on sectionals:

Telephone.......(800) 626-3677 toll free, U.S. only
Telephone.......(301) 344-6341 local, MD, VA, DC
E-mail...............9-AMC-Aerochart@faa.gov

(IIRR Tinker in this group may have provided that contact info) and reported it along the lines of of something ``It appears to me either there's a discrepancy on the radius of MFR airspace on your sectional ( or ATC at MFR has a misunderstanding. I read it as 4.1nm on your chart, 5nm per ATC. If I`m reading that wrong let me know. If it's an error on your chart please not accordingly. If not perhaps you could advise ATC at MFR.``

Got a prompt email and telephone and courteous response from Rich Fecht there.

To make a short story shorter he then contacted the tower manager and got it straighted out with as far as I could tell with no drama..... controllers are being advised to correct the misunderstanding.

This I bet is actually a relief for them because in at least one of my conversations one reported some frustration with how close to incurring or even incurring some pilots appeared to him to be skirting their airspace without making contact. And a relief to me as it was a bit disconcerting to be told I was 3/4th inside their airspace when iFly was telling me I had cleared it.

As I said elsewhere.... remaining question is along the lines of ``how rare or common are such misreadings of perimeters at the towers.`` if I had to guess I`d say not common, and less so at class C, B, and A.

Prudent practice still IMO is cut the perimeter a bit of slack if I don't want to deal with their airspace.

Thanks to all who contributed, particularly Jim and Tinker for persisting.

Alex