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Question: Where is Airway Width Defined

Width of Federal Airways

I know that Federal airways are 4 nm on each side of the centerline, but I can’t find it in the FARs or directly in the AIM. At one point there was a FAR, 14 CFR &sect 71.75 that said, “(b) Unless otherwise specified:
(1) Each Federal airway includes the airspace within parallel boundary lines 4 miles each side of the center line.” However, that section of the FARs no longer exists. The AIM still references the 4nm width in a section talking about leading a turn so as to remain in protected airspace. 5-3-5 “… width of an airway or route, i.e., 4 nautical miles on each side of the centerline.”

The question is, where is the width defined?

Answer: The primary area referred to in the title of paragraph 1720 is defined in TERPS handbook paragraph 1711 as follows: “The primary en route obstacle clearance area extends from each radio facility on an airway or route to the next facility. It has a width of 8 NM; 4 NM on each side of the centerline of the airway or route.” This definition of primary area describes the basic protected airspace along the centerline of a Federal airway and makes no reference to general off- airway terrain and obstruction clearance requirements. NTSB Safety Recommendation A-98-81 through -82 (PDF)

The primary obstacle clearance area has a protected width of 8 nautical miles (NM) with 4 NM on each side of the centerline. (Link)

Exclusion of Santa Barbara and Farallon islands from Class A airspace

Class A airspace is defined to exclude “Santa Barbara Island, Farallon Island”. This makes absolutely no sense. Even though they are more than 12 miles from the coast, they are in the Pacific High so they should be Class A above 18,000′ MSL. And at that height, you’d have a hard time knowing that you were over them since they are so small. Any idea why they are excluded?

Offshore High/Low and Control Areas

Has anyone come across a map (on-line or otherwise) of the Offshore High/Low and Control Areas? I know that the Pacific High covers most of the Pacific, including Guam and Hawaii, but I can’t find a map of it. Same thing for the Atlantic High.


I know that the TERPS defines instrument approaches, but while I’ve found lots of references to it, I’ve never seen a link to it.

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