If flying IFR heading 135, what would be the definition of a legal cruising altitude?

Question

If flying IFR heading 135, what would be the definition of a legal cruising altitude?

Answer 1

Your assigned altitude.

Answer 2

Yes, whatever ATC assigns you

Answer 3

Odd thousands when flying IFR between 0 degrees and 179 degrees.  Even thousands flying IFR 180 degrees to 360 degrees.

ATC will assign an altitude if the one you request does not work for them, for some reason.

Answer 4

As John B and others say, it's the altitude assigned to you by ATC.  Expect an odd number of thousands of feet, followed by zeros, when flying east of due north or south, but they can assign you other altitudes at their discretion.

And occasionally they will do funny things.  A friend of mine filed out on the dials the other day in a Cherokee 235, and was assigned FL260 for a portion of the flight.  He had to ask for an amendment.

Fends off boredom.

Answer 5

§ 91.179   IFR cruising altitude or flight level.....

Unless otherwise authorized by ATC, the following rules apply—

(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).

Answer 6

"In controlled airspace....maintain.....the altitude...assigned....by ATC."