Flight Levels


#1

I was told by someone at a Flight Simulator Forum that Aircraft follow certain rules when it comes to Flight Levels. I was told:

Course 0*-179*
Odd Altitudes to FL290
Then FL330
Then FL370
Then every 4,000’

Course 180*-359*
Even Altitudes to FL280
Then FL310
Then FL350
Then every 4000’

Yet, when I watch real flights, they seem to break all the “rules.” When I flew in a Continental Boeing 727-200 from Cleveland to San Francisco in 1984, we flew at FL370! On the return, in 1985, we flew at the same altitude!

Does anyone know if the above rules are correct or did they change after 1985? Or does the Flight Level depend on whatever ATC says?

Thanks,

seeker737


#2

FAR 91.159 sayeth (note that essentially everything in the US above FL180 is controlled airspace):

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 in non-RVSM airspace, 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).

(4) When operating at flight level 290 and above in airspace designated as Reduced Vertical Separation Minimum (RVSM) airspace and

(i) On a magnetic course of zero degrees through 179 degrees, any odd flight level, at 2,000-foot intervals beginning at and including flight level 290 (such as flight level 290, 310, 330, 350, 370, 390, 410); or

(ii) On a magnetic course of 180 degrees through 359 degrees, any even flight level, at 2000-foot intervals beginning at and including flight level 300 (such as 300, 320, 340, 360, 380, 400).


#3

…But you’re partially correct, ATC can and does sometimes issue instructions contrary to the standard.


#4

Thanks for that detailed explanation. It answers a couple questions I have always had with FS9 and FSX and my own real-life experience on that flight to California and back where we flew at FL370 in both directions. I guess it is possible for the AI aircraft to be flying at FL300 or FL320 which I have observed so often in FS. It appeared MS had just taken the lazy approach for those planes and were using Even Altitudes for West and Odd Altitudes for East. Since it is a “Simulator,” I guess we can “Simulate” RVSM conditions.

Thanks again for that fine clarification.