Definition
The section of the Federal Aviation Regulations that prescribes the cruising altitudes and flight levels VFR aircraft must use when operating in level cruising flight more than 3,000 feet above the surface. It assigns odd-thousand-foot altitudes plus 500 feet (e.g., 3,500; 5,500; 7,500) for magnetic courses of 0° through 179°, and even-thousand-foot altitudes plus 500 feet (e.g., 4,500; 6,500; 8,500) for magnetic courses of 180° through 359°.
Plain English
This is the rule that tells VFR pilots which altitudes to fly at when cruising. If you're flying roughly eastbound, you pick an odd thousand plus 500 feet. If you're flying roughly westbound, you pick an even thousand plus 500 feet. It only applies above 3,000 feet over the ground.
Context Anchor
Seen in FAA handbook discussions when comparing visual-flight cruising altitude rules with instrument-flight cruising altitude rules.
Derivation
CFR' stands for Code of Federal Regulations — the official compilation of U.S. federal rules. 'Part 91' is the chunk of those rules covering general aviation operating rules, and '91.159' is one specific numbered section within that part. The numbering system lets pilots and the FAA point to an exact rule quickly.
Why Pilots Care
Following this regulation prevents mid-air collisions by ensuring VFR aircraft fly at altitudes different from those typically used by IFR traffic on the same route.
Intuition Check
Do not read this as a handbook paragraph number or a checklist step. It is a legal regulation citation: it points to the rule a pilot must follow.
Example Sentence 1
Planning a VFR cross-country eastbound at 7,500 feet satisfies 14 CFR 91.159 because the magnetic course is less than 180° and the altitude is an odd thousand plus 500.
Example Sentence 2
The pilot checked 14 CFR 91.159 to confirm the correct VFR cruising altitude before departure.