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. A magnetic course of exactly 180° is treated as '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

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

The reasoning is what makes it 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. The result is a layered structure of traffic — eastbound IFR at 5,000, eastbound VFR at 5,500, westbound IFR at 6,000, westbound VFR at 6,500. It is predictable and routine, which is exactly what is needed when an aircraft closing from the other direction may not be visible.

Three clarifications carry more weight than the rest of the regulation combined:

• Magnetic course, not heading. Course is the intended ground track — the line on the chart. Heading is where the nose is pointing to fight a crosswind. § 91.159 applies to the track, not the nose.
• Above 3,000 AGL, not MSL. This is the most common misread of the rule. The floor follows the terrain. Departing a 6,000-foot field, the rule does not apply until above 9,000 MSL.
• 18,000 MSL is the ceiling. Above 18,000 is Class A — IFR only — and altitude is assigned by ATC.

What an Examiner Asks About § 91.159

This is a quick-recall regulation on the oral. Examiners typically are not looking for a textbook recitation — they are looking for whether the applicant can apply the rule in flight, in seconds, without hesitation. Common versions include:

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

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

Here is how this plays out on a planning sheet rather than a knowledge-test card. Consider planning a westbound VFR cross-country, magnetic course 270°, with an initial instinct to file 7,500 MSL because it clears the terrain with room to spare.

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, the aircraft is well above the floor. § 91.159 applies.

Step 2 — What direction is the flight 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). Flying it westbound busts § 91.159 and places the aircraft nose-to-nose with eastbound VFR traffic. 8,500 is the correct choice — the next legal westbound altitude up.

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

Pilots who get into trouble with this rule are usually not the ones who do not know it. They are the ones who memorize "odd east, even west, plus 500" and never connect it to the chart in front of them. The rule works best as a planning habit, not a quiz answer.