A lot of new pilots plan a cross-country around the winds and terrain and only later realize the altitude they picked is the wrong kind for their direction of flight. It is an easy mistake, and one I now check on every trip. Here is how the VFR cruising altitude rule works and how I apply it.
What the VFR Cruising Altitude Rule Says
The rule lives in 14 CFR 91.159. When you are flying VFR in level cruising flight, more than 3,000 feet above the surface, and below 18,000 feet MSL, you pick an altitude based on your magnetic course. It does not apply in the traffic pattern or while climbing and descending, and it is not a clearance from ATC.
The pattern is simple:
- Magnetic course 0 to 179 degrees (eastbound): odd thousands plus 500 feet, such as 3,500, 5,500 or 7,500.
- Magnetic course 180 to 359 degrees (westbound): even thousands plus 500 feet, such as 4,500, 6,500 or 8,500.
The shortcut I use is “east is odd, west is even, and always add the 500.”
Course, Not Heading
This is where students slip up. The rule is written around your magnetic course, which is the path you are making over the ground, not the heading you are holding on the compass. With a strong crosswind your heading can differ from your course by ten or twenty degrees. Usually that makes no difference. If your course is close to due north or due south, though, you could land on the wrong side of the 180-degree line.
My habit is to take the magnetic course from the flight plan or chart, pick the altitude from that, and not change it because the wind pushed my heading around.
Why the Rule Exists
The point is vertical separation. If everyone heading east flies odd altitudes and everyone heading west flies even ones, two airplanes on opposite courses along the same road, river or airway are separated by 500 feet at least instead of meeting at the same altitude. It does not replace see-and-avoid. Aircraft are climbing, descending and wandering all the time, and not everybody follows the rule.
Picking an Altitude in Practice
The rule tells you which altitudes are legal for your direction. It does not tell you which one is best. I weigh a few things:
- Terrain and obstacles: I want comfortable clearance above the highest point on my route, not just the minimum.
- Clouds and visibility: VFR cloud clearance and visibility requirements still apply, so a layer of broken clouds may decide the altitude for me. I read the current conditions first, and my METAR reading guide covers how I do that.
- Winds aloft: A few thousand feet can mean a noticeable change in groundspeed. I will take the better wind if the other items allow it.
- Engine and passengers: Higher means thinner air, lower performance and a longer climb. If I am carrying a full load on a warm day, I do not want to be too ambitious.
I also write my chosen altitude in the navlog with the course next to it, so I can see at a glance that the two agree.
Descending and Changing Course
On a long trip the course may change from eastbound to westbound, for example when you turn at a checkpoint. When that happens I make the altitude change part of the turn: I check the new magnetic course, decide on the new altitude, and make the change cleanly instead of putting it off. If I am talking to ATC, I tell them what I am planning, and I follow any clearance or instruction I receive. Their instructions override the cruising altitude rule. I covered that kind of radio contact in my flight following guide.
Common Mistakes I See
The most frequent one is forgetting the 500. People remember odd or even and fly 5,000 instead of 5,500. The second is using the heading instead of the course. The third is treating the rule as optional once they are above a certain altitude, when it applies all the way up to, but not including, 18,000 feet MSL. And the fourth is never checking the altitude after a route change.
It also belongs in your risk planning. I list altitude choices alongside the other limits in my personal minimums because a sensible altitude gives me margin for terrain, weather and engine trouble.
Bottom Line
For VFR cruising altitudes, remember that eastbound is odd thousands plus 500 and westbound is even thousands plus 500, based on your magnetic course, when you are more than 3,000 feet above the ground and below 18,000 feet MSL. Then use judgment: terrain, weather, winds and your airplane’s performance decide which legal altitude is the right one for the day. Check it before takeoff and again whenever your course changes.
