The Maximum Elevation Figure, the Little Numbers in the Corner of Every Sectional Square, and Planning a Cross-Country Altitude That Actually Clears the Rocks

The Maximum Elevation Figure (MEF) is the pair of numbers printed in the middle of each latitude-longitude rectangle on a sectional chart. It represents the highest known terrain or obstacle inside that box, plus a safety buffer - meaning if you’re at or above that altitude anywhere in the rectangle, you’ll clear everything below. Used correctly, the MEF is the fastest way to set a cross-country cruising altitude that actually clears the rocks.

What Is the Maximum Elevation Figure on a Sectional Chart?

A sectional is divided by lines of latitude and longitude into rectangles. Each box is bounded by a full degree of latitude and a full degree of longitude, which on a sectional works out to roughly 30 nautical miles tall.

Printed in the middle of each box is a pair of numbers - a large figure and a smaller one beside it. Read them together as thousands and hundreds of feet. A large 1 with a smaller 3 means 1,300 feet. A large 8 with a smaller 5 means 8,500 feet.

That single value is the MEF for that rectangle.

What Does the MEF Actually Represent?

The MEF represents the highest known feature inside the box - terrain or obstacle, whichever is taller. Chartmakers take the tallest thing in the rectangle, whether a mountain ridge or a radio tower, then add a buffer.

That buffer accounts for three things: the height of the obstacle itself, the fact that antennas and guy wires can reach above a tower’s published tip, and a margin for an unverified obstacle that might be slightly taller than what’s on record.

So the MEF is not the elevation of the ground and not the top of the mountain. It’s a promise: everything in this box lives below this number. It’s a terrain and obstruction ceiling, written on the chart, for every 30-mile square of the country.

How Do I Use the MEF to Choose a Cross-Country Cruising Altitude?

Most pilots pick a cruise altitude for the wrong reasons - a round number, a friendly winds-aloft forecast, or simply what they flew last time. The first question that actually matters is: what is the tallest thing between me and my destination, and am I flying over it or into it?

The MEF answers that at a glance. Here’s the drill:

1. Draw your course line.
2. Look at every box your line passes through.
3. Find the highest MEF along the route.

That highest MEF is your floor - the lowest altitude at which you know for certain you’re clearing everything on the route.

Say your course runs through three rectangles. The first reads 2,400, the second (with a ridge line) reads 5,100, and the third drops to 3,200. The number you care about is 5,100. If any part of your route dips below that while crossing the middle box, you’re betting you personally know where the high terrain is and can avoid it in real time - sometimes in haze, sometimes at night. Don’t make that bet.

How Much Margin Should I Add Above the MEF?

Take the highest MEF and build up from there using the standard rule of thumb: stay at least 1,000 feet above the highest obstacle in flat country, and closer to 2,000 feet in mountainous terrain, so you have room to glide and think if the engine gets quiet.

Using the example above, take the 5,100 MEF, add your buffer, and you’re looking at roughly 6,100 to 7,000 feet - before you’ve even considered winds or airspace.

Notice what happened: the terrain picked your minimum altitude. Not the round number, not the winds. Everything else - winds aloft, fuel burn, airspace shelves - stacks on top of the floor the MEF gave you. That’s the order of operations: terrain first, comfort and efficiency second.

What Are the Common Traps With the MEF?

Trap 1: The MEF is not a legal altitude. It doesn’t tell you how high you’re allowed or required to fly. It’s not an airway minimum, a sector altitude, or clearance from controlled airspace. Your VFR hemispheric rule and airspace are a separate conversation. The MEF just keeps you from hitting the planet.

Trap 2: The MEF applies to the entire box, not your course line. The obstacle that set the number might be 40 miles off to the side. That can feel overly cautious, but respect it anyway - you won’t fly a perfect string down your magenta line. Wind pushes you, you dodge clouds, you take vectors and divert around showers. Real flying happens in a smear around the line, and the MEF protects the whole box. That buffer is a feature, not a bug.

Trap 3: Don’t confuse the MEF with other terrain numbers. Spot elevations mark the height of a specific point. Obstacle heights next to towers are given as height above ground and above sea level. On IFR charts you’ll find the OROCA (Off-Route Obstruction Clearance Altitude), MOCA, and MEA. They’re cousins answering the same question - how low can I safely be - but they’re calculated differently. For a VFR cross-country on a sectional, the MEF is your quick terrain read.

A Real-World Scenario: When the Winds Fool You

You’ve planned a two-hour cross-country to visit a friend a couple of valleys over. You chose 5,500 feet because the winds aloft were kind there and it kept you comfortably under the Bravo shelf.

But you led with the winds, not the terrain. Go back and scan the MEFs, and there it is - one box in the middle third of the trip reads 6,300. You were going to cross it at 5,500, eight hundred feet below the highest known thing in that box, possibly at night, trusting a dark windscreen. That’s exactly the setup that shows up in accident reports as controlled flight into terrain: a good airplane and a capable pilot flown into rising ground that was on the chart the whole time.

So you replan, terrain first. Highest MEF is 6,300. You want at least 1,000 feet of margin - more over rising terrain - so you bump cruise to 7,500 feet. Then you check the winds up there, confirm you’re still clear of the Bravo, verify the airplane will actually climb to and hold 7,500 on a warm day with two people and bags, and recheck your fuel burn. Same trip, completely different margin - all from reading a number that was printed on the chart before you ever bought the airplane.

How Does the MEF Connect to the ACS and the Checkride?

Cross-country planning is a required area of operation, and the Airman Certification Standards (ACS) specifically want to see that you can select appropriate cruising altitudes considering terrain and obstructions. That’s the language, and the MEF is the single most efficient tool on a sectional for demonstrating that skill.

When the examiner asks why you chose your cruise altitude, don’t say “because it seemed good.” Walk them through it: “My highest MEF along the route was X. I wanted this much margin above it for the terrain and my glide options. That set my minimum. Then I layered on the hemispheric rule, the winds aloft, and the airspace, and that’s how I landed on this altitude.” That answer shows you understand what the numbers protect you from.

The 90-Second Habit That Keeps You Safe

Reading a chart well is a perishable skill, and the terrain scan is easy to shortcut when you’re tired and the flight is tomorrow morning. But this step costs about 90 seconds: run your finger down the course line box by box, say the MEFs out loud, find the biggest one, and build up from there.

Do it even on routes you think you know cold - the flight where you skip it is exactly the flight where the ceiling is lower than forecast and you end up scud running down a valley you assumed you understood.

And keep the habit in the air. Plans change: you get a diversion, weather, or decide to cut a corner. The moment you leave your planned line, ask yourself what the MEF is of the box you’re drifting into, and whether you’re still above it. That’s the number that keeps a diversion from becoming a much worse day.

Key Takeaways

• The MEF is the highest known terrain or obstacle in a chart box (roughly 30 nautical miles per side) plus a safety buffer - at or above it, you clear everything below.
• Plan terrain first: find the highest MEF along your course, then add 1,000 feet of margin in flat country or 2,000 feet in mountains before considering winds and airspace.
• The MEF is not a legal altitude and applies to the entire box, not just your course line - so the protection covers real-world drift and diversions.
• Don’t confuse the MEF with spot elevations, obstacle heights, or IFR figures like OROCA, MOCA, and MEA.
• The ACS expects you to select cruising altitudes considering terrain and obstructions - the MEF is the fastest way to demonstrate it.