FAR Ninety-One One Fifty-Nine, the VFR Cruising Altitude Rule, and Why 'East Is Least, West Is Best' Keeps You From Meeting Someone Head-On at a Hundred and Ninety Miles an Hour

FAR 91.159, the VFR cruising altitude rule, requires pilots in level VFR flight more than 3,000 feet above the surface to choose their altitude based on their magnetic course. Fly an odd thousand plus 500 when headed east (a course of 0° through 179°) and an even thousand plus 500 when headed west (180° through 359°). The rule stacks opposite-direction traffic 1,000 feet apart so two airplanes flying toward each other are never on the same sheet of air.

Why the VFR Cruising Altitude Rule Exists

Picture a Cessna 172 heading east from Ohio toward Pennsylvania and a Piper Cherokee heading west on the same clear afternoon. Both are flying VFR, both are looking outside, and both are perfectly legal. The trouble starts if both pilots pick the same nice round number - say 5,500 feet - because now they are pointed directly at each other.

A head-on meeting between two light airplanes is not gentle. A Skyhawk cruises around 120 knots, and so does the Cherokee. Nose to nose, the gap closes at roughly 240 knots - better than 270 miles per hour.

At that closure rate, you may have about 10 seconds from the moment the other airplane becomes a recognizable shape to impact. An airplane coming straight at you is the hardest thing to spot in the sky, because it doesn’t track across your windscreen. It sits in one spot and slowly grows larger, giving your eye no motion to catch.

The FAA’s fix is elegant: if we can’t guarantee pilots will see each other, make sure opposite-direction airplanes are never at the same altitude to begin with. Stack eastbound traffic on one set of floors and westbound traffic on another, and even if nobody sees anybody, they pass with 1,000 feet of daylight between them.

How Does FAR 91.159 Actually Work?

The rule applies only when you are more than 3,000 feet above the ground and in level VFR cruise. Below that, you’re maneuvering, departing, or setting up to land, so locking you into specific altitudes would just get in the way.

Everything then depends on your magnetic course - the direction you’re actually traveling over the ground, not the heading your nose points after the wind pushes you around.

• Eastbound (course 0° through 179°): fly an odd thousand plus 500 - 5,500, 7,500, 9,500, and so on.
• Westbound (course 180° through 359°): fly an even thousand plus 500 - 4,500, 6,500, 8,500.

The memory aid that has lived in pilots’ heads for generations: east is least, west is best. East gets the lower, odd numbers (1, 3, 5, 7, 9); west gets the higher, even numbers (2, 4, 6, 8).

Why the Extra 500 Feet?

The plain thousands belong to IFR traffic - the airplanes on an instrument flight plan in the system. They get the round numbers like 5,000, 6,000, and 7,000. VFR pilots get the altitudes in between, the ones ending in 500.

The result is a layered cake: IFR eastbound, IFR westbound, and tucked 500 feet above each of those, the VFR traffic going the same direction. Everyone is stacked, everyone is separated, and nobody shares a floor with someone coming the other way.

Magnetic Course, and Only in Level Cruise

Two things trip up students every time. First, it’s your magnetic course, not your heading. Second, the rule pins you only when you’re straight and level in cruise.

When you’re climbing to altitude or descending out of it, the rule doesn’t apply - you pass through all those altitudes on the way. Ask yourself the simple question: Am I level, more than 3,000 feet above the ground, going somewhere? If yes, then which way am I going, and does my altitude match?

How Do I Pick My Cruising Altitude for a Cross-Country?

Say you’re flying about 80 miles to the northeast for a hundred-dollar hamburger. You plot your course and it comes out to 055° - northeast, which falls in the easterly half (0° through 179°).

East is least: odd plus 500. Your legal choices are 5,500, 7,500, or 9,500, depending on terrain, winds, and how high you feel like climbing.

On the way home, you turn around and your course becomes the reciprocal, about 235° - the westerly half. West is best: even plus 500, so you might come home at 4,500 or 6,500.

Notice what happened: same route, out and back, but you flew home at a different altitude than you flew out. That is exactly the point. Every airplane doing the same trip you just did is stacked a thousand feet away instead of swimming straight at you.

What About a Course That’s Due North or Due South?

Due east (090°) is easterly and odd. Due west (270°) is westerly and even. The boundaries are where students hesitate. A course of due south (180°) falls into the westerly bucket (180° through 359°), so you’d fly even plus 500. Due north (360°/0°) sits at the very edge and is generally grouped with the easterly, odd side.

Don’t sweat the half-degree at those cardinal boundaries. Use good judgment, pick the appropriate side, and above all keep your eyes outside - near those boundaries you may have traffic legally at your altitude approaching from an angle. The rule protects you best from the head-on threat; it does not replace looking out the window.

The Rule Is Your Friend Even When It Doesn’t Apply

Even at 2,500 feet above the ground - below where the reg bites - you can still think like the rule. If you’re droning eastbound on a cross-country with no terrain or airspace forcing your hand, choosing an altitude that keeps you clear of the westbound crowd costs you nothing and stacks the deck in your favor.

That matters because midairs almost never happen in bad weather. They happen on gorgeous, severe-clear afternoons when the flying is easy and everyone’s guard is down. They happen near airports and along popular cross-country routes, where good VFR days funnel everyone down the same valleys, along the same shorelines, and over the same checkpoints. The nice days are the busy days.

Two Systems Working Together

FAR 91.159 is not a force field. Plenty of legal traffic will be below 3,000 feet, maneuvering, on a local flight, or crossing your path at an angle at your exact altitude - with every right to be there.

So let the altitude rule handle the head-on geometry, the worst and hardest-to-see case, and handle everything else with a disciplined scan:

• Lower the nose occasionally to clear the area beneath you.
• Move your eyes across the windscreen in sections, pausing to let each chunk of sky come into focus.
• Clear the area before every turn.

The rule stacks the traffic; your scan catches what the rule can’t.

Your Next Flight: Plan the Altitude on Purpose

Don’t pick your cruising altitude as an afterthought once you’re already level. Choose it when you plot your course. Look at your magnetic course line, ask east or west, say the rhyme, and select an altitude that is legal for your direction, high enough to clear terrain and airspace, and low enough to stay out of oxygen requirements while leaving a comfortable glide toward somewhere friendly. Write it on your nav log and own it before you start the engine.

Then, on the way home, remember to change it - the reciprocal course flips you to the other side of the rule. This is exactly what a checkride examiner wants to see: not just that you can recite the numbers, but that you chose your altitude on purpose and can explain why, weighing direction, terrain, airspace, weather, and glide options.

The sky only looks empty up there. Pick your altitude on purpose, keep your eyes moving, and give the other pilot his thousand feet.

Key Takeaways

• FAR 91.159 applies to level VFR flight more than 3,000 feet above the surface.
• Eastbound (course 0°–179°): fly odd thousands plus 500 (5,500 / 7,500 / 9,500). Westbound (180°–359°): fly even thousands plus 500 (4,500 / 6,500 / 8,500).
• The rule is based on magnetic course, not heading, and stacks opposite traffic 1,000 feet apart.
• The extra 500 feet keeps VFR traffic separated from IFR traffic, which uses the plain thousands.
• The rule stops the head-on threat; a continuous visual scan handles the crossing and angled traffic it can’t.