VFR cruising altitudes and the hemispheric rule, east is odd, west is even, the half-circle that keeps you from meeting traffic head-on

SUMMARY: Learn the VFR hemispheric rule—east is odd, west is even—and how to pick a legal, safe cruising altitude on every cross-country leg.

The VFR hemispheric rule keeps opposite-direction traffic vertically separated by assigning cruising altitudes based on your magnetic course. If your magnetic course is 0° to 179° (easterly), you fly odd thousands plus 500 feet (3,500, 5,500, 7,500). If it’s 180° to 359° (westerly), you fly even thousands plus 500 feet (4,500, 6,500, 8,500). The rule applies under FAR 91.159, but only when you’re more than 3,000 feet above the ground.

What Problem Does the Hemispheric Rule Solve?

Picture two airplanes on reciprocal courses—one eastbound, one westbound—both cruising at exactly 6,500 feet because it was a nice round number with a good view. Each is doing about 120 knots, which means a closing speed of roughly 240 knots, better than four nautical miles per minute.

Here’s the cruel part: an airplane on a direct collision course doesn’t slide across your windscreen. It sits in one spot and slowly grows larger, which is the single hardest target for the human eye to detect. By the time it’s obvious, you have seconds.

The solution is elegant. Instead of relying on pilots to spot each other in time, the rule simply ensures that opposite-direction traffic is never at the same altitude in the first place. It slices the compass in half and assigns each half its own set of altitudes.

How Does the East-Is-Odd, West-Is-Even Rule Work?

Picture a compass rose divided into two halves.

If your magnetic course is 0° to 179°, you’re heading into the easterly half of the circle, and you fly odd thousands plus 500 feet: 3,500, 5,500, 7,500, and so on.

If your magnetic course is 180° to 359°, you’re in the westerly half, and you fly even thousands plus 500 feet: 4,500, 6,500, 8,500.

East is odd. West is even. Everyone adds the extra 500 feet on top.

Now apply it to our two airplanes. The eastbound pilot on a course of 090° flies odd plus 500, so he’s at 7,500 feet. The westbound pilot on the reciprocal course of 270° flies even plus 500, so she’s at 6,500 feet. That’s 1,000 feet of vertical separation between two airplanes that were pointed straight at each other. They pass, never see one another, and both make it home. That’s the rule doing its quiet job.

When Does the Hemispheric Rule Actually Apply?

The rule only kicks in when you’re more than 3,000 feet above ground level (AGL)—not above sea level. This is the detail that trips up the most pilots.

FAR 91.159 specifically says more than 3,000 feet above the surface. So in the pattern, in the practice area, or on a short hop where you never climb that high, the hemispheric rule simply doesn’t apply. You can fly any altitude you like, terrain and airspace permitting.

The reasoning makes sense. Down low, pilots are maneuvering, taking off, landing, and doing air work. Forcing everyone onto rigid altitudes there wouldn’t help. It’s the cruise portion of flight, up higher where everyone is pointed somewhere with purpose, that the rule earns its keep.

Watch the AGL distinction carefully. If you’re flying over Denver, where the ground is already a mile up, 3,000 feet AGL is a very different altimeter reading than it is over the Florida coast. Always know your ground elevation—the rule lives in the AGL world, not the altimeter world.

Is the Rule Based on Heading or Course?

It’s magnetic course, not heading. This distinction matters.

Your heading is where the nose is pointed. Your course is the actual path of the airplane over the ground—the line you drew on the chart. On a windy day you might be crabbing 10 or 15 degrees off to one side just to hold your line, so your heading and your course are different numbers.

The rule cares about the course. Where you’re actually going, not where the nose happens to be pointing to get you there.

How Do You Find Magnetic Course on the Chart?

This is where it gets genuinely confusing for new pilots, and nobody likes to admit it.

You measure your course on the chart against the lines of longitude, which gives you true course. Then you apply magnetic variation—the local difference between true north and magnetic north—to get your magnetic course. It’s that magnetic course that decides east or west.

In most of the country, variation is only a handful of degrees, so it rarely flips you from one half of the circle to the other. But near the boundaries, on a course already close to 0° or 180°, those few degrees can absolutely push you across the line.

Fly a course of about 178° magnetic and you’re easterly—odd plus 500. Add just two degrees to 180°, and suddenly you’re westerly—even plus 500. The boundary is real, and it’s exactly where you have to be most careful.

A Real Cross-Country Example

You’re planning a flight from your home field to a small airport about 90 nautical miles to the northeast.

You draw and measure your line. True course comes out to 045°. Variation in your area is 6° west, so you add it, giving a magnetic course of about 051°. That’s solidly in the easterly half, so you owe odd thousands plus 500.

Now you weigh the other factors. The terrain says you want comfortable margin over the ridges. The winds aloft forecast shows a nice tailwind around 7,000. The Class B or C shelves leave you room. So you pick 7,500 feet—odd plus 500, legal for an easterly course, and it puts the wind at your back. The rule is working with you.

Then comes the trip home. Same airports, reversed. Your magnetic course is now the reciprocal, about 231°—westerly. Now you owe even thousands plus 500.

You cannot come home at 7,500 just because it was comfortable on the way out. On a westbound course, 7,500 is the wrong side of the rule—you’d be flying an eastbound altitude straight into oncoming traffic. Coming home, it’s 6,500 or 8,500. Pick one.

What’s the Most Common Mistake Pilots Make?

Flying the same altitude home that they used on the outbound leg.

A reciprocal course at the same altitude puts you directly in the head-on lane. Every cross-country has at least two legs, and every leg gets its own altitude check. Plan each direction independently.

How Do You Demonstrate This on a Checkride?

On the private pilot checkride, cross-country planning lives in the navigation area of operations, and the examiner will have you plan a real flight to a real airport.

Don’t just announce “I’ll be at 6,500.” Tell the story:

“My magnetic course on this leg is 240°—that’s westerly—so I’m flying even plus 500, and I chose 6,500 for terrain clearance and a favorable wind.”

The examiner wants to hear that you can connect the altitude to the rule and to your reasons. Anybody can memorize “east is odd.” The applicant who passes is the one who can explain the half-circle and apply it to the actual line they drew.

Expect a probe like, “Does this rule even apply on this leg?” If your whole cross-country stays below 3,000 feet AGL, the correct answer is no—91.159 doesn’t require a specific cruising altitude there, though you’d still pick something sensible and keep your eyes outside. Knowing when a rule doesn’t apply is just as sharp as knowing when it does.

Practical Steps for Your Next Flight

Force the order in your nav log. Add a column for magnetic course and put cruising altitude right next to it. Write the course first, then the altitude, so the altitude is a consequence of the course—not a guess.

Say it out loud during planning. “Easterly course, odd plus 500.” It feels silly at the kitchen table. It will save you in the airplane.

Remember the order of priorities. The hemispheric rule narrows you to a set of legal altitudes. From that menu, you choose based on terrain clearance, airspace, winds aloft, oxygen needs up high, cloud bases, and your own comfort. The rule gives you the menu; conditions help you order off it.

Use the rule to aim your traffic scan. If you’re westbound at an even-plus-500 altitude, the opposite-direction traffic is most likely 1,000 feet above or below you at the odd-plus-500 altitudes. It’s not a guarantee—plenty of pilots are climbing, descending, or flying low—but it focuses your scan. The rule isn’t just a constraint on you; it’s a hint about everybody else.

Why This Rule Is Worth Getting Right

This one isn’t trivia to cram before the oral. The hemispheric rule is one of the small number of regulations that exists purely because someone didn’t follow it and two airplanes met in the middle of the sky.

When you fly your altitude correctly, you’re not satisfying an examiner. You’re keeping 1,000 feet of air between yourself and a stranger you’ll never see. The full details come straight from FAR 91.159 and the FAA’s Pilot’s Handbook of Aeronautical Knowledge, both worth reading in your own copy.

Key Takeaways

• East is odd, west is even: magnetic course 0°–179° flies odd thousands + 500; course 180°–359° flies even thousands + 500.
• The rule applies only above 3,000 feet AGL under FAR 91.159—not above sea level, and not at low altitudes.
• It’s based on magnetic course (your line over the ground), never heading.
• Plan each leg separately—the return trip is a reciprocal course and almost always requires a different altitude.
• The rule narrows you to legal altitudes; terrain, airspace, and winds aloft determine the best choice from that set.