Vfr Cruising Altitude or Flight Level

Section 91.159 sets VFR cruising altitudes — the 'hemispheric rule' that separates eastbound VFR traffic from westbound VFR traffic by altitude.

Above 3,000 AGL up to 18,000 MSL:

• Magnetic course 0° through 179° (basically east): Odd thousands plus 500 feet (3,500, 5,500, 7,500, 9,500, 11,500, 13,500, 15,500, 17,500 MSL)
• Magnetic course 180° through 359° (basically west): Even thousands plus 500 feet (4,500, 6,500, 8,500, 10,500, 12,500, 14,500, 16,500 MSL)

The 'plus 500' feet: The 500-foot offset puts VFR traffic between IFR cruising altitudes. IFR uses 3,000, 4,000, 5,000, 6,000, etc. (full thousands). VFR uses 3,500, 4,500, 5,500, etc. This 500-foot vertical separation between VFR and IFR is the foundation of the airspace structure.

Below 3,000 AGL: The hemispheric rule does NOT apply. Below 3,000 AGL, the pilot may cruise at any altitude appropriate for the operation, terrain clearance, and traffic considerations.

Above 18,000 MSL: Class A — VFR is not permitted. The hemispheric rule continues as 'flight levels' (IFR-only) per § 91.179.

Memory aid: 'Odd East, Even West, plus 500 for VFR' — captures the structure. For magnetic course exactly 180° you're heading 'westward' (180° is part of the 180-359° range).

Why this works: Two aircraft on a head-on reciprocal course at different altitudes (one eastbound, one westbound) will have at least 1,000 feet of vertical separation. Combined with the 'see and avoid' rule, the hemispheric structure dramatically reduces the chance of a midair on opposing tracks.

Reference: AIM 3-1-5 on Cruising Altitudes; FAA-H-8083-25 (PHAK) Chapter 16 on flight planning.

East-Odd-Plus-500, West-Even-Plus-500 — § 91.159 Decoded

Here's the rule in one breath: above 3,000 feet AGL and below 18,000 feet MSL, in level cruise flight, your VFR altitude is dictated by your magnetic course. Heading east (000° through 179°), you fly odd thousands plus 500. Heading west (180° through 359°), you fly even thousands plus 500. That's the whole regulation in a sentence.

But the why is what makes this stick. § 91.159 is the hemispheric separation principle in action. VFR aircraft going opposite directions are stacked 1,000 feet apart from each other, and 500 feet offset from the IFR traffic on the full thousands. It's a layered cake of traffic — eastbound IFR at 5,000, eastbound VFR at 5,500, westbound IFR at 6,000, westbound VFR at 6,500. Predictable. Boring. Exactly what you want when you can't see the airplane closing on you from the other direction.

Three clarifications worth more than the rest of the regulation combined:

• Magnetic course, not heading. Course is your intended ground track — the line on the chart. Heading is where the nose is pointing to fight a crosswind. § 91.159 cares about the track, not the nose.
• Above 3,000 AGL, not MSL. This is the most common misread on the books. The floor follows the terrain. Departing a 6,000-foot field, the rule doesn't apply until you're above 9,000 MSL.
• 18,000 MSL is the ceiling. Above 18,000 is Class A — IFR only — and your altitude is whatever ATC tells you it is.

What an Examiner Asks About § 91.159

This is a quick-recall regulation on the oral. Examiners aren't looking for a textbook recitation — they're looking for whether you can apply the rule in flight, in seconds, without thinking about it. Expect some version of these:

• "What's the VFR cruising altitude for a magnetic course of 240°?" 240° is westbound (180–359), so even-thousand plus 500. Pick from 4,500, 6,500, 8,500, 10,500 — whichever fits the terrain and your performance.
• "Below 3,000 AGL, does the rule apply?" No. You can cruise at any altitude appropriate for terrain, traffic, and clouds.
• "When does it stop applying as you climb?" At 18,000 MSL. Above that, you're in Class A, you need an IFR clearance, and ATC assigns the altitude.
• "Is the rule based on heading or course?" Course — your intended ground track. A 10-knot crosswind doesn't change which hemispheric altitude you're legally required to fly.
• The trick question: "You're crossing a ridge at 2,500 AGL. Does § 91.159 apply?" No. The rule only kicks in above 3,000 AGL. But the examiner is also checking whether you remembered § 91.119 (minimum safe altitudes) and your terrain clearance margin. Answer both.

Picking Your Altitude on a Real Cross-Country, Under § 91.159

Here's how this plays out on a planning sheet, not a knowledge-test card. You're planning a westbound VFR cross-country, magnetic course 270°, and your first instinct is to file 7,500 MSL because it puts you above the terrain with room to spare. Let's walk it.

Step 1 — Is the rule in play? Terrain along the route averages 2,000 MSL, so 3,000 AGL is roughly 5,000 MSL. At 7,500, you're well above the floor. § 91.159 applies.

Step 2 — What direction are you going? Magnetic course 270° is squarely westbound (180–359). That means even thousand plus 500.

Step 3 — Is 7,500 legal? No. 7,500 is an eastbound VFR altitude (odd plus 500). If you fly that westbound, you've just busted § 91.159 and placed yourself nose-to-nose with eastbound VFR traffic. Pick 8,500 instead — next legal westbound altitude up.

Step 4 — Does the altitude actually work? Now check it against the rest of your planning. Are you above any MEA or MOCA you might need for terrain clearance on the chart? Is 8,500 above your engine's service-ceiling fade and still gives you reasonable true airspeed? Does the winds-aloft forecast favor 8,500 or push you up to 10,500? § 91.159 sets the legal floor of altitude choice — terrain, performance, and winds set the practical one.

The pilots who get into trouble with this rule aren't the ones who don't know it. They're the ones who memorize "odd east, even west, plus 500" and never connect it to the chart in front of them. Throttle On — make the rule a planning habit, not a quiz answer.