2. An appropriate ATC clearance has been received
ATC Clearance Requirement
Flights shall not be made in IFR conditions within controlled airspace until an ATC
clearance has been obtained.
IFR Cruising Altitude or Flight Level
Unless otherwise authorized by ATC, the following rules apply:
1. In controlled airspace Each person operating an aircraft under IFR in level
cruising flight in controlled airspace shall maintain the altitude or flight level (FL)
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 CFR 91.159.
2. 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:
When operating below 18,000 feet MSL
o 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)
o 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)
When operating at or above 18,000 feet MSL but below FL 290
o On a magnetic course of zero degrees through 179 degrees, any
odd FL (such as 190, 210, or 230)
o On a magnetic course of 180 degrees through 359 degrees, any
even FL (such as 180, 200, or 220)
When operating at FL 290 and above in non-RVSM airspace
o On a magnetic course of zero degrees through 179 degrees, any
FL, at 4,000-foot intervals, beginning at and including FL 290 (such
as FL 290, 330, or 370)
o On a magnetic course of 180 degrees through 359 degrees, any
FL, at 4,000-foot intervals, beginning at and including FL 310 (such
as FL 310, 350, or 390)
When operating at FL 290 and above in airspace designated as Reduced
Vertical Separation Minimum (RVSM) airspace
o On a magnetic course of zero degrees through 179 degrees, any
odd flight level, at 2,000-foot intervals beginning at and including FL
290 (such as FL 290, 310, 330, 350, 370, 390, 410)
8-18
