FAR Ninety-One Point One Fifty-Nine, the VFR Cruising Altitudes Rule, and Why East Is Odd Keeps You From Meeting Someone Head-On at a Mile a Minute
FAR 91.159's hemispheric rule keeps VFR traffic separated by altitude - here's how 'east is odd' works and why it matters.
Under FAR 91.159, when you’re flying VFR in level cruise more than 3,000 feet above the ground, your altitude is set by your direction of travel: eastbound courses (0° up to but not including 180° magnetic) fly odd thousands plus 500 feet, and westbound courses (180° up to but not including 360°) fly even thousands plus 500 feet. The rule guarantees that airplanes flying opposite directions are stacked at least 1,000 feet apart vertically - a passive safety net for traffic that will never see or talk to each other. Remember it as “east is odd.”
What Does FAR 91.159 Actually Say?
The rule is a separation system, not bookkeeping. Out in the wide-open airspace where no controller is assigning altitudes, it’s the primary thing standing between you and traffic you’ll never see coming.
It applies only when three conditions are all true:
- You’re operating under VFR (visual flight rules)
- You’re more than 3,000 feet above the surface - above ground level, not sea level
- You’re in level cruising flight
When those three things are true, your altitude is no longer a free choice. It’s determined by your magnetic course.
How Do the East/West Altitude Rules Work?
Take your magnetic course - the direction you’re actually traveling over the ground, corrected for magnetic variation. Not your heading. Your course. Then look at where it falls on the compass.
Eastbound (magnetic course 0° up to but not including 180°): fly odd thousands plus 500 feet. That’s 5,500, 7,500, or 9,500.
Westbound (magnetic course 180° up to but not including 360°): fly even thousands plus 500 feet. That’s 4,500, 6,500, or 8,500.
That’s the entire rule. East is odd. West is even. And everyone in visual conditions above 3,000 AGL adds the extra 500 feet on top.
The memory trick that has saved more written-test points than any other: east is odd. Both words feel short and sharp, and they line up in your mind. West and even are the leftovers - burn in “east is odd” and the rest falls into place, because west has to be the other one.
Why Is the Rule Built This Way?
Picture two airplanes on exactly reciprocal courses - one eastbound, one westbound, nose to nose. Without any rule, both could be at 7,000 feet, and physics would sort out the rest, and it would not sort it out kindly.
Now apply the rule. The eastbound airplane is on an odd-plus-500 altitude - say 7,500. The westbound airplane is on an even-plus-500 altitude, and the nearest options are 6,500 and 8,500. So the closest that opposite-direction traffic can legally be, vertically, is 1,000 feet apart.
That’s the whole point. You could have your head down in the cockpit fussing with a chart, and the airplane coming straight back at you is 1,000 feet above or below you by regulation.
Why Add the Extra 500 Feet?
Because of IFR traffic. Airliners and everyone on an instrument flight plan fly the plain thousands - 6,000, 7,000, 8,000, on the whole numbers.
When you, as a VFR pilot, add that extra 500 feet, you’re separated from opposite-direction VFR traffic and tucked 500 feet away from all the IFR traffic flying the round numbers through the same sky. That 500 feet is deliberate - a buffer between the see-and-avoid world and the controlled, talking-to-a-controller world. You’re threading right between them.
Who Assigns These VFR Altitudes?
Nobody. On a VFR cross-country, no controller is going to call and tell you to climb and maintain 7,500. You pick it, based on your course, and ideally you pick it on the ground during planning.
This is a rule you enforce on yourself - which is exactly why it’s so easy to blow off. There’s no voice reminding you. It’s on you.
What Does “More Than 3,000 Feet Above the Surface” Really Mean?
This condition trips up applicants and certificated pilots alike. The magic number is measured above ground level (AGL) - above the terrain underneath you, not above sea level.
If the ground below you sits at 1,000 feet of elevation, the rule doesn’t start biting until you’re above 4,000 feet on your altimeter, because that’s 3,000 feet of air between you and the dirt.
In practice, this means the rule does not apply down low - in traffic-pattern altitudes or in the practice area where you’re doing maneuvers at 2,000 or 3,000 AGL. The low-altitude environment is full of airplanes climbing, descending, and entering the pattern, and forcing everyone onto odd-and-even steps down there wouldn’t help. The rule is for cruise, up higher, where two airplanes might hold a steady altitude on a steady course for 20, 30, or 40 minutes at a time.
Does the Rule Apply While Climbing or Descending?
No. The third condition is level cruising flight. When you’re climbing to your cruise altitude or descending toward your destination, the rule isn’t pinning you to a step - you climb through whatever you climb through.
It’s when you level off and settle in that the number has to be right. Cruise means cruise.
How Do I Apply This on a Real Cross-Country?
Say you’re planning a leg on a magnetic course of 090° - due east - over terrain around 1,000 feet of elevation, and you want to climb over some haze, so you’re eyeing 6,000 feet.
Stop. 090° is eastbound, and east is odd. Six thousand is an even thousand with no 500 on it - that’s not yours at all. Your legal options going east are 5,500, 7,500, or 9,500. Over that low terrain, both 5,500 and 7,500 are more than 3,000 AGL, so the rule is in force. Come down to 5,500 or climb to 7,500.
Coming home on the reciprocal course of 270° - due west - your altitudes flip to 4,500, 6,500, or 8,500. If you flew out at 7,500, you come back at 6,500 or 8,500 - automatically 1,000 feet different, because you reversed direction. The system did that for you.
Course or Heading - Which One Counts?
The line is drawn at your course, not your heading. On a windy day with a stiff crosswind, you’ll be crabbing - nose pointed one way while you track another. The rule cares about your magnetic course, the actual direction you’re moving over the ground. Plan it off the course line on your chart, not off where the nose happens to point.
What About Due North or Due South?
The edges are defined precisely. A course of exactly 180° (due south) falls into the westbound, even group. Due north - 360° or 0° - is odd. Remember: 0° up to but not including 180° is the odd side; 180° up to but not including 360° is the even side. If you’re flying nearly north or south, know which side of that line your course falls on and commit to it - don’t split the difference.
How Is This Tested on the Checkride?
The examiner wants to see that you understand cruising altitude selection during cross-country planning and that you can apply it in the airplane. When you level off on a cross-country leg and pick an altitude, the examiner is quietly noting whether it matches your course.
If you’re eastbound and you level at an even-plus-500 - or worse, a plain thousand - that’s a red flag. The Airman Certification Standards (ACS) folds this directly into cross-country flight planning and the pilotage and dead reckoning tasks, expecting you to select an appropriate altitude considering terrain, weather, airspace, and the cruising altitude rule. It’s not trivia in a corner - it’s woven into how you plan every cross-country.
Know your course, know your altitude, and say it out loud as you level off.
Practical Takeaways for the Cockpit
Decide your altitude on the ground. Plan it off your magnetic course line for each leg during preflight planning. When you already know this leg is 7,500 and the way home is 6,500, you’re not doing math at 200 feet per minute in a climb.
Watch your height above terrain, not just the altimeter. The trigger is 3,000 feet AGL. Over rising terrain, you can climb into the rule’s jurisdiction without your altimeter number changing - the ground simply came up to meet you.
Say it out loud when you level off - every time. “Course is 090, that’s east, east is odd, 7,500, confirmed.” That verbal habit is the single best defense against leveling at a wrong altitude out of pure inertia.
Key Takeaways
- FAR 91.159 requires VFR aircraft in level cruise more than 3,000 feet AGL to fly specific altitudes based on magnetic course.
- Eastbound (0°–179°): odd thousands plus 500 (5,500 / 7,500 / 9,500). Westbound (180°–359°): even thousands plus 500 (4,500 / 6,500 / 8,500). Remember “east is odd.”
- The rule guarantees opposite-direction traffic is separated by at least 1,000 feet vertically, and the extra 500 feet keeps VFR traffic clear of IFR aircraft flying the plain thousands.
- The 3,000-foot trigger is measured above ground level, and the rule applies only in level cruise - not during climbs, descents, or low-altitude maneuvering.
- No controller assigns these altitudes - you select them yourself during planning, based on your magnetic course, not your heading.
Radio Hangar. Aviation talk, built by pilots. Listen live | More articles