Federal Aviation Regulation Ninety-One Point One Fifty-Nine, VFR Cruising Altitudes, and the East-Is-Odd Rule That Keeps Two Airplanes From Meeting Head-On at the Same Number

Above 3,000 feet AGL on a VFR cross-country, Federal Aviation Regulation 91.159 determines your cruising altitude based on your magnetic course. If your course is 0° through 179° (eastbound), you fly odd thousands plus 500 feet (5,500, 7,500, 9,500). If it’s 180° through 359° (westbound), you fly even thousands plus 500 feet (4,500, 6,500, 8,500). The shorthand every instructor teaches: east is odd, plus five hundred.

What Problem Does the VFR Cruising Altitude Rule Solve?

A clear VFR day makes the sky look empty, but that emptiness is an illusion. Airplanes funnel toward the same airports, along the same shorelines, down the same valleys, and across the same navaids and waypoints that everyone’s tablet drew a magenta line through.

When traffic funnels onto the same route, some airplanes are heading out and others are coming back, on the same line at the same time. If everyone simply picked a pleasant round number, two pilots who both like 4,500 end up nose to nose with a combined closure of a couple hundred knots and almost no time to react.

The FAA’s solution is elegant: divide the altitudes by direction of flight. When everyone follows the rule, airplanes going one way are always at least 1,000 feet above or below airplanes going the other way. The vertical separation is baked into the number you chose before takeoff - even if neither pilot ever spots the other.

When Does FAR 91.159 Apply?

The rule kicks in when you are more than 3,000 feet above the surface on a VFR cruise. Below that threshold, you’re maneuvering, climbing, descending, and working the pattern and practice area, so locking yourself to a cruising altitude would do more harm than good.

Above 3,000 AGL, the rule is in play - and it’s based on your magnetic course, the direction you are actually traveling over the ground, corrected for wind. Not your heading. That distinction is exactly what checkride examiners probe.

How Do I Pick the Right VFR Cruising Altitude?

Split the compass in half along the north-south axis:

• Magnetic course 0°–179° (eastbound): odd thousands + 500 → 5,500, 7,500, 9,500
• Magnetic course 180°–359° (westbound): even thousands + 500 → 4,500, 6,500, 8,500

Picture it in the air. You’re flying a magnetic course of 090° (due east), so east is odd and you climb to 7,500. An airplane coming back the other way at 270° (due west) flies west-is-even, putting them at either 6,500 or 8,500. You end up a full 1,000 feet away from oncoming traffic you may never even see. That’s the whole idea - a backup for the eyeballs when see-and-avoid fails, and it does fail. A head-on airplane is a tiny, motionless dot that doesn’t grow until the last few seconds.

Is It Magnetic Course or Heading? (The Mistake Examiners Watch For)

Use course, not heading. Say you want a magnetic course of 090° but a stiff south wind forces you to crab, pointing the nose at 075°. Your heading is 075°; your course is 090°. Pick your altitude off the course - 090°, eastbound, odd plus 500.

On a windy cross-country, glance at the track readout on your GPS rather than the heading indicator when double-checking your altitude. Track is course. That’s your answer.

Which Way Is Due North and Due South?

The dividing line runs straight down the north-south axis, so the boundary cases matter:

• Due south (180°) falls in the westbound bucket → even plus 500.
• Due north (360°, or 0°) is eastbound → odd plus 500.

Everything on the eastern semicircle is odd; everything on the western semicircle is even. If your course sits almost due north or almost due south, be deliberate about which side of 180° and 360° you’re actually on.

Does This Rule Apply to IFR Flights?

No. FAR 91.159 governs VFR cruising altitudes. Under IFR, a different rule applies and air traffic control assigns your altitude. Be aware that VFR-on-top clearances and IFR flights in visual conditions shift the cruising-altitude expectations depending on which rules you’re operating under. For a plain VFR cross-country above 3,000 AGL, this is your rule: east is odd plus 500, west is even plus 500.

Why the Extra 500 Feet?

The 500-foot offset is deliberate and not optional. IFR and airline traffic cruise on the even and odd thousands right on the nose - IFR eastbound on the odd thousands, IFR westbound on the even thousands. VFR traffic is tucked 500 feet into the gaps so the see-and-avoid crowd and the folks getting vectors in the clouds don’t stack up on the exact same numbers. When you report 5,500, 7,500, 4,500, or 6,500, that 500 feet is the point of the rule, not sloppiness.

Worked Example: The Same Route, Two Different Legal Altitudes

Plan a cross-country to an airport about 140 miles away. You draw your line on the sectional and measure a true course of 100°, then correct for magnetic variation to get a magnetic course of about 105°. That’s eastbound (0°–179°), so east is odd: your legal altitudes are 5,500, 7,500, 9,500, and so on. Factoring in winds aloft, terrain, and your airplane’s happy cruise, you choose 7,500 - terrain clearance, a decent tailwind, and fully legal.

Two days later you fly home. Same route reversed, your magnetic course is now about 285° - westbound, so west is even. You cannot use 7,500 anymore; you’d pick 6,500 or 8,500. Same airplane, same route, opposite direction, different set of legal altitudes. The altitude that was legal outbound is illegal on the way back the moment you turn around.

Examiners look for exactly this in cross-country planning. Plan an eastbound leg at 4,500 and it’s a red flag, because 4,500 is a westbound altitude. The Airman Certification Standards call out selecting appropriate cruising altitudes in the cross-country and navigation tasks - a gimme once you’ve internalized east is odd.

Does This Replace See-and-Avoid?

No - it’s a layer, not a replacement. You will occasionally meet an airplane coming the other way at your altitude. Maybe they’re within 3,000 feet of the ground and legally exempt, maybe they’re climbing or descending through your altitude, maybe they simply aren’t following the reg.

The cruising altitude rule stacks the odds in your favor, but you still keep your eyes outside, clear your turns, use flight following when you can get it, and treat every altitude like someone might be at it. The regulation is the belt; your eyeballs are the suspenders. Wear both.

There’s even a scanning bonus. Eastbound at 7,500, you know legal westbound traffic will be at 6,500 or 8,500 - roughly your altitude plus or minus 1,000 feet, out ahead of you. The rule doesn’t just separate you; it tells you where to look.

Key Takeaways

• FAR 91.159 applies to VFR flight more than 3,000 feet above the surface; below that you’re exempt.
• Altitude is set by magnetic course, not heading, and magnetic, not true.
• East is odd: course 0°–179° = odd thousands + 500 (5,500, 7,500, 9,500). West is even: course 180°–359° = even thousands + 500 (4,500, 6,500, 8,500).
• The rule builds in 1,000 feet of vertical separation from opposing traffic even when neither pilot sees the other.
• The same route flown in reverse requires a different legal altitude - always recheck your direction.