The Maximum Elevation Figure, the Little Blue Number in Every Grid on Your Sectional, and How It Keeps You Above the Tallest Thing You Cannot See at Night

The Maximum Elevation Figure (MEF) is the faded blue number printed in every grid square on a sectional chart, and it represents the tallest known obstacle or terrain in that block - plus a safety buffer - rounded up to the next hundred feet. If you fly at or above the MEF, you are guaranteed to clear everything the chart makers know about inside that square. It is the single fastest way to answer the most important question in night or low-visibility flying: how high do I have to be to clear the tallest thing I cannot see?

What Is the Maximum Elevation Figure on a Sectional Chart?

Open any sectional and you’ll see the whole chart carved into a grid by faint lines of latitude and longitude. On a standard sectional, each of those squares covers 30 minutes of latitude by 30 minutes of longitude - roughly a block of country.

Look toward the middle of any square and you’ll find two numbers stacked together: a large digit with a smaller one riding above it. If it reads a large 1, 2 and a small 5, that’s 125. Because MEFs are printed in hundreds of feet, that means 12,500 feet above sea level.

That number is the Maximum Elevation Figure for that block of chart.

What Does the MEF Actually Guarantee?

The MEF promises you that somewhere inside that square is the single tallest thing the chart makers know about - a mountain peak, a ridge, or a radio tower. The FAA takes that tallest obstacle and does two things worth understanding:

First, it starts with the height of the tallest obstacle above sea level. Then it adds a buffer to account for the obstacle’s own vertical structure and the possibility that its exact top isn’t perfectly surveyed. Finally, it rounds the whole figure up to the next hundred feet - up, never down.

So the MEF is not the height of the terrain, and it’s not the height of the tower. It’s the height of the tallest thing in that block, plus margin, rounded up. At or above it, you’re above everything the chart knows about in that square.

One critical distinction that trips up students every time: the MEF is not an altitude you are cleared to fly. It is not a legal minimum safe altitude. It is a fact about the ground - it tells you the top of the world underneath you. What you do with that fact is where your judgment comes in.

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

There are two ways to use the MEF: one quick, one careful.

The quick way is a whole-route floor. When you draw your course line, look at every grid square the line passes through, find the highest MEF among them, and write it down. That single number is the tallest thing anywhere near your route. Stay at or above it, and terrain and towers are simply not part of your flight.

Here’s a scenario. You draw a line from your home field to an airport 110 nautical miles away. The line crosses six grid squares, and you read the MEFs in order: 2,200 – 2,600 – 3,100 – 4,400 – 3,800 – 2,900. The biggest is 4,400 feet.

Now you know. If you cruise at 5,500 feet, you’re 1,100 feet above the tallest obstacle on the entire route - before you even worry about which specific square it lives in. That’s a clean, defensible number you can brief to yourself out loud, and it’s exactly the kind of altitude reasoning the Airman Certification Standards want to hear on a checkride: a pilot who chose an altitude on purpose.

The careful way reads the MEFs square by square as you cross the country. Most routes aren’t uniformly high - maybe your leg is mostly flat with one ridge in the middle. Flying the entire leg at the height of that one ridge might cost fuel, push you into weather, or just be pointless. So you build a terrain profile in your head - low, low, low, here comes the high one, back to low - and plan your altitude to ride the terrain instead of ignoring it.

Why Does the MEF Matter Most at Night and in Low Visibility?

In daylight and good visibility, you can often see an obstacle and maneuver around it. Mostly. But flying isn’t planned for the easy days - it’s planned for the day visibility drops, the sun goes down, or you end up lower than intended because of clouds, terrain, or a headwind that ate your altitude budget.

On those days, your eyeballs aren’t enough. The number on the chart becomes the difference between a boring flight and a very short one. That’s why the MEF earns its keep on a moonless night over unfamiliar country, when the windshield shows you nothing and there’s a tower somewhere out in the black.

What Are the MEF’s Limitations?

The MEF is powerful, but it isn’t omniscient. Three things trip pilots up:

It doesn’t tell you where in the square the tall thing is. The obstacle could be tucked in a far corner, nowhere near your course line. A high MEF doesn’t automatically mean you’re about to hit something - it flags the block, and your eyes find the actual obstacle or terrain contour.

Not every obstacle is charted. Obstacles below a certain height above the ground may not appear as individual symbols. That’s one more reason to give yourself a healthy pad above the MEF rather than skimming it by a hundred feet.

It only knows the permanent world. The MEF is built from known, fixed obstacles and terrain. It doesn’t know about the crane that went up last Tuesday or a temporary tower. That’s why your required preflight action includes checking current notices (NOTAMs) for your route. The chart tells you about the permanent world; the notices tell you what changed since the chart was printed. You need both.

How Do I Build the MEF Into My Cross-Country Planning?

A number you never write down is a number you’ll never use. Your nav log already has a column for planned altitude - add one habit to the way you fill it in.

1. As you plot each leg, run your finger along the course line and call out the MEFs the line touches, out loud: “2,200… 2,600… 4,400…”
2. Circle the highest MEF for the leg.
3. Choose a cruising altitude that clears it with room to spare, satisfies your direction of flight under the hemispheric (cruising altitude) rule, and keeps you out of any weather.

That’s three constraints working at once - terrain from the MEF, direction from the hemispheric rule, and weather from your briefing - and the altitude you pick is the one that satisfies all three. That’s real cross-country planning, a world away from penciling in 5,500 because the last pilot did.

How Much Buffer Should I Add Above the MEF?

Set a personal terrain buffer and write it into your personal minimums on the ground, when you’re calm. Common practice is to fly at least 1,000 feet above the highest MEF at night over flat country, and 2,000 feet or more over rising terrain, because mountain winds and downdrafts do things to your altitude that flat-land flying never taught you.

Decide your pad ahead of time. Don’t try to negotiate terrain clearance with yourself at night while an updraft shoves you around.

Bring it back to that black night. You’re level, the panel is glowing, the windshield shows nothing, and there’s a tower out there. But you drew your line this afternoon, read every grid square it crossed, found the highest MEF at 4,400 feet, and set your cruise at 6,500 feet - a 2,100-foot pad for night over rising ground. That tower you can’t see? You’re more than 2,100 feet above the block it lives in. It isn’t a threat. It isn’t even a factor. It’s a fact on a map you accounted for hours ago at your kitchen table.

Key Takeaways

• The Maximum Elevation Figure (MEF) is the tallest known obstacle or terrain in a grid square, plus a buffer, rounded up to the next hundred feet - printed in hundreds of feet in each 30-by-30-minute square.
• At or above the MEF, you clear everything the chart knows about in that square, but it is not a clearance altitude or a legal minimum - it’s a fact about the ground.
• For a quick floor, find the highest MEF your course line touches and stay above it; for efficiency, read MEFs square by square and ride the terrain.
• The MEF doesn’t show where the obstacle sits, doesn’t include every low obstacle, and can’t know about new or temporary structures - always check NOTAMs.
• Set a personal buffer in advance: roughly 1,000 feet above the highest MEF at night over flat land, 2,000+ feet over mountains.