Ninety-One One Fifty-Nine, the VFR Cruising Altitudes, and Why East Is Odd, West Is Even, and Everybody Adds Five Hundred Above Three Thousand Feet

FAR 91.159 is the VFR cruising altitude rule, and it comes down to one phrase: east is odd, west is even, and everybody adds five hundred. When your magnetic course points east (000° up to but not including 180°), you cruise at an odd thousand plus 500 feet - 5,500, 7,500, 9,500. When it points west (180° up to but not including 360°), you cruise at an even thousand plus 500 - 4,500, 6,500, 8,500. The rule applies in level VFR flight more than 3,000 feet above the ground and below 18,000 feet (FL180), and its entire purpose is to keep opposite-direction traffic vertically separated when nobody is watching your altitude.

Why does the VFR cruising altitude rule exist?

Picture two small airplanes on the same route between two towns, one flying east and one flying west, both VFR, both legal, both looking out the window. If they both pick 6,000 feet, they are now aimed directly at each other. The closure rate between two light airplanes can top 300 knots.

You do not have time to react to that. By the time an oncoming airplane grows from a dot into something you recognize, you have seconds, not minutes.

The FAA’s solution was elegant: if the sky is uncontrolled and nobody can watch everyone, at least guarantee that eastbound and westbound traffic are never at the same altitude. Stack them. Give each direction its own set of altitudes, with 500 feet of vertical cushion built in, so even when two airplanes point right at each other, they pass with room to spare.

That is the whole idea. It is a traffic-separation system that works without anyone talking on the radio, because the protection is baked into the numbers.

How do I figure out the correct VFR cruising altitude?

Start with your magnetic course - the direction your airplane actually travels over the ground, corrected for wind. Then ask one question: am I going generally east or generally west?

• Magnetic course 000° to 179° (up to but not including 180°) = eastbound = odd thousand + 500 → 5,500, 7,500, 9,500
• Magnetic course 180° to 359° (up to but not including 360°) = westbound = even thousand + 500 → 4,500, 6,500, 8,500

The mental process in the cockpit is one quick check: which way am I going? East wants an odd-thousand-and-a-half. West wants an even-thousand-and-a-half. The +500 is universal in VFR cruise, so treat it as a constant, not a variable.

The memory trick that makes it stick: don’t memorize four separate numbers. Memorize the split and memorize that east is odd - the “E” and the word “odd.” West is simply the other one, and the plus 500 is always tacked on.

When does FAR 91.159 actually apply?

The rule kicks in when you are more than 3,000 feet above ground level (AGL) - not 3,000 feet on your altimeter, but 3,000 feet above the terrain directly below you.

Below that trigger - in the pattern, on climbout, maneuvering in the practice area at 2,000 AGL - the rule does not apply. Down low you are climbing, descending, and maneuvering, and forcing rigid altitudes there would do more harm than good.

The upper boundary is 18,000 feet (FL180). At and above that you are in Class Alpha airspace, where everyone is IFR by definition, so the VFR cruising rule simply doesn’t reach that high. In short, the rule lives between 3,000 feet AGL and 18,000 feet, in level cruising flight.

There are also two small exceptions written into the regulation: you are exempt while turning and while holding in a holding pattern of two minutes or less. The rule governs level cruising flight - once you settle in, wings level, going somewhere, the altitude must match your direction. Maneuvering is temporary, so it’s excused.

Why is it magnetic course and not heading?

This is the point examiners love to test. Your heading is where the nose points. Your course is where the airplane actually tracks over the ground.

On a windy day those differ. You might be crabbed 20 degrees into a crosswind - nose pointed one way, airplane traveling another. The rule cares about your track across the ground, because that is your true direction of travel and that is what must be separated from oncoming traffic.

So when you compute your cruising altitude, use your track: the magenta course line, your true course corrected to magnetic. Don’t use the wobbling number on the compass.

Why do VFR pilots add 500 feet?

The extra 500 feet is what makes this a VFR rule, and it’s clever. Aircraft on IFR clearances fly the plain thousands - 5,000, 6,000, 7,000, right on the number.

When you are VFR and add 500 feet, you deliberately tuck yourself into the gap between the IFR altitudes. A VFR airplane at 7,500 sits 500 feet above IFR traffic at 7,000 and 500 feet below IFR traffic at 8,000. The half-thousand isn’t decoration - it keeps VFR and IFR traffic from ever sharing the same shelf.

Worked example: a round-trip cross country

Fly from a town on the west side of your state to a city on the east side. Your magnetic course works out to 075°. That’s less than 180°, so you’re eastbound - odd plus 500. Your legal options are 5,500, 7,500, 9,500, and so on.

Say terrain, winds, and cloud bases make 7,500 the sweet spot. You’re legal, and you’re stacked correctly against anyone coming back the other way, who by rule will be at an even-plus-500 like 6,500 or 8,500 - a clean 1,000 feet away.

Now you have lunch, turn around, and fly home. Your magnetic course is now 255°, which is more than 180°, so you’re westbound - even plus 500. Now you want 6,500 or 8,500. You cannot legally cruise at 7,500 going home, even though that’s exactly where you were comfortable an hour ago.

Same route, opposite direction, different altitude. That’s the rule doing its job - it moved you off the altitude where the oncoming traffic lives.

Why this rule matters even when you fly alone

This is a see-and-avoid rule that works when see-and-avoid fails. Human eyes are genuinely bad at catching an airplane on a constant collision course, because a converging airplane doesn’t move across your windshield - it sits in one spot and slowly grows. Our eyes are drawn to motion, and the one target that matters most is the one that isn’t moving.

The hemispheric rule is the backstop for exactly that failure. On the hazy afternoon when you never saw the other airplane and he never saw you, if you were both following the rule, you passed with 500 or 1,000 feet of vertical space and never knew how close the geometry could have been.

But the system only works if everyone plays. The eastbound pilot is counting on the westbound pilot to be at an even-plus-500. The moment one pilot decides the rule doesn’t matter today, the protection collapses for both of them - which is why you fly the correct altitude even when nobody is watching.

What if ATC assigns me a different altitude?

If you’re receiving flight following or operating in busy airspace and a controller assigns you an altitude, follow the assignment. An ATC instruction takes precedence, and you are not busting FAR 91.159 by complying.

The hemispheric rule is your default in the uncontrolled, unassigned world - what you fly when the sky is quiet and the decision is yours. And for most of your VFR cross-country flying, that decision is yours.

Practical steps for your next cross country

1. Compute altitude when you compute course. The moment you know your magnetic course, ask east or west and pick the altitude from the correct set right there on the planning sheet - don’t leave it for the cockpit.
2. Expect outbound and inbound to differ. If your route runs mostly east–west, your altitudes home and back will almost never match. That’s normal; that’s the rule working.
3. Watch the 3,000 AGL trigger over changing terrain. The rule follows the ground beneath you, not the altimeter. Over rising terrain you can cross into the rule’s territory even without climbing. When in doubt in cruise, just fly the correct hemispheric altitude - complying is never wrong.
4. Use track, not heading. On a strong-wind day, don’t let the crab angle push you into using your compass heading.
5. Honor ATC assignments. An assigned altitude overrides the default rule.

Key Takeaways

• East is odd, west is even, and everybody adds 500 - the core of FAR 91.159.
• Eastbound (course 000°–179°): odd thousands + 500 → 5,500 / 7,500 / 9,500. Westbound (course 180°–359°): even thousands + 500 → 4,500 / 6,500 / 8,500.
• The rule applies more than 3,000 feet AGL and below 18,000 feet (FL180), in level cruising flight.
• Base your altitude on magnetic course (your track), not heading - critical on windy days.
• The +500 tucks VFR traffic between the plain-thousand IFR altitudes; exceptions apply while turning or holding two minutes or less.