91.179

[CitationLover]

91.179 states:

§ 91.179 IFR cruising altitude or flight level.

(a) In controlled airspace. Each person operating an aircraft under IFR in level cruising flight in controlled airspace shall maintain the altitude or flight level assigned that aircraft by ATC. However, if the ATC clearance assigns "VFR conditions on-top," that person shall maintain an altitude or flight level as prescribed by § 91.159.

(b) In uncontrolled airspace. Except while in a holding pattern of 2 minutes or less or while turning, each person operating an aircraft under IFR in level cruising flight in uncontrolled airspace shall maintain an appropriate altitude as follows:

(1) When operating below 18,000 feet MSL and --

(i) On a magnetic course of zero degrees through 179 degrees, any odd thousand foot MSL altitude (such as 3,000, 5,000, or 7,000); or

(ii) On a magnetic course of 180 degrees through 359 degrees, any even thousand foot MSL altitude (such as 2,000, 4,000, or 6,000).

(2) When operating at or above 18,000 feet MSL but below flight level 290, and --

(i) On a magnetic course of zero degrees through 179 degrees, any odd flight level (such as 190, 210, or 230); or

(ii) On a magnetic course of 180 degrees through 359 degrees, any even flight level (such as 180, 200, or 220).

(3) When operating at flight level 290 and above, and --

(i) On a magnetic course of zero degrees through 179 degrees, any flight level, at 4,000-foot intervals, beginning at and including flight level 290 (such as flight level 290, 330, or 370); or

(ii) On a magnetic course of 180 degrees through 359 degrees, any flight level, at 4,000-foot intervals, beginning at and including flight level 310 (such as flight level 310, 350, or 390).



if above 18,000 is class A, which by definition is CONTROLLED (even E above 14,500 is this also), why put items (b)(2) and (b)(3) in? am i missing something?

 

[Booker]

Courtesy of AvWeb:

http://www.avweb.com/news/system/182429-1.html

Basically, the article states it's in case a flight goes NORDO while in VMC inside Class A airspace.

Booker

 

[A Squared]

Courtesy of AvWeb:

http://www.avweb.com/news/system/182429-1.html

Basically, the article states it's in case a flight goes NORDO while in VMC inside Class A airspace.

Booker

well, that doesn't quite address the question. The AVweb article addresses VFR flight in Class A airspace, however the questions asks why the regulation addresses IFR flight in *uncontrolled airspace* above 18,000 ft.

The answer is that not all airspace above 18,000 ft is class A airspace. If you take a look at the basic definition of Class A airspace in Part 71, it excludes some areas in Alaska, Hawaii, and over some named islands. The comprehensive definition of Class A airspace is in FAA order 7400.9, which presumably exists someplace, but I haven't seen it. If you were to sit down with 7400.9 and a big map and painstakingly follow all the of the part designating CLass A aispace, I suspect that you would find that there are some limited areas within the jurisdiction of the United States where there is no Class A or other controlled airspace above 18,000 feet. 91.179 (b)(2) and (b)(3) would be the rules for flying IFR in that Uncontrolled airspace above 18,000 feet.

regards

 

[Booker]

The comprehensive definition of Class A airspace is in FAA order 7400.9, which presumably exists someplace, but I haven't seen it.

Look harder (or just write to the feds). There's an old copy at http://ntl.bts.gov/data/911.pdf. I'd be interested to see where any gaps would exist. But just to clarify, would such uncontrolled areas under US control not be designated Class G by defualt? The AIM states if airspace isn't designated in classes A through E, it is Class G.

B

 

[midlifeflyer]

But just to clarify, would such uncontrolled areas under US control not be designated Class G by defualt? The AIM states if airspace isn't designated in classes A through E, it is Class G.

Because Class G ends at 14,500, where the default becomes Class E

 

[Booker]

Because Class G ends at 14,500, where the default becomes Class E

Ah, but if that's true, there is no uncontrolled airspace above 14,500, which takes us back to square one.

B

 

[midlifeflyer]

Ah, but if that's true, there is no uncontrolled airspace above 14,500, which takes us back to square one.

Didn't say there wasn't any. Just that it becomes the default.

For both the above 14,500 and above 18,000 general rules, there are some specific exceptions. An area which met the exceptions in both of the following rules would be Class G above 18,000 msl.

§ 71.33 Class A airspace areas.
(a) That airspace of the United States, including that airspace overlying the waters within 12 nautical miles of the coast of the 48 contiguous States, from 18,000 feet MSL to and including FL 600 excluding the states of Alaska and Hawaii, Santa Barbara Island, Farallon Island, and the airspace south of latitude 25°04'00" North.
(b) That airspace of the State of Alaska, including that airspace overlying the waters within 12 nautical miles of the coast, from 18,000 feet MSL to and including FL 600 but not including the airspace less than 1,500 feet above the surface of the earth and the Alaska Peninsula west of longitude 160°00'00" West.

and

§ 71.71 Class E airspace.
Class E Airspace consists of:
(a) The airspace of the United States, including that airspace overlying the waters within 12 nautical miles of the coast of the 48 contiguous states and Alaska, extending upward from 14,500 feet MSL up to, but not including 18,000 feet MSL, and the airspace above FL 600, excluding -
(1) The Alaska peninsula west of longitude 160°00'00" W.; and
(2) The airspace below 1,500 feet above the surface of the earth.

 

[Booker]

OK, just to make sure I understand this now: The Alaska example you provide contains Class A airspace as listed in 7400.9 within the following boundaries:

Control 1234H
That airspace extending upward from 18,000 feet MSL to and including FL 450 within an area bounded by a line beginning at lat. 58”06’57’’N., long. 160”00’00’’W.; south along long. 160”00’00”W. until it intersects the Anchorage Air Route Traffic Control Center boundary; thence southwest, northwest, north, and northeast along the Anchorage Air Route Traffic Control center boundary to lat. 62°35’00’N., long. 175”00’00’’W.; to lat. 59”59’57’’N., long, 168”00’08’’W.; to lat. 57”45’57’’N., long. 161”46’08’’W.; to the point of beginning.

So would I be correct in inferring that the airpsace above FL450 in this area would be Class G? (I admit, it would be some kind of fun to cancel IFR and cruise at FL475 in a G-V.)

Thanks!
B

 

[CitationLover]

only the government could come up with crap like this....

 

[midlifeflyer]

only the government could come up with crap like this....

My guess is that the 160W longitude one involves a treaty issue.