The Maximum Elevation Figure, the Little Blue Number in the Middle of Every Sectional Quadrangle That Tells You How Low Is Too Low

The Maximum Elevation Figure (MEF) is the blue number printed inside each quadrangle of a VFR sectional chart, and it represents the elevation of the tallest known terrain or obstacle in that box, plus a small buffer, rounded up. It is not a minimum safe altitude - it simply tells you the top of the highest thing in that quadrangle. Your job as a pilot is to read the MEFs along your route, find the highest one, and build a cruising altitude with real margin on top of it.

What Is the Maximum Elevation Figure on a Sectional Chart?

Every sectional is divided by thin blue lines of latitude and longitude into boxes called quadrangles. Each quadrangle covers 30 minutes of latitude by 30 minutes of longitude.

Inside each box, the chart makers print one number that represents the highest object in that quadrangle - the highest terrain or the highest obstacle, whether that’s a mountain peak, a ridge line, or a radio tower.

The number appears as two stacked figures: a large number for thousands of feet and a smaller number beside it for hundreds. A large 4 next to a smaller 5 means 4,500 feet.

If the box reads 4,500, the chart is telling you that somewhere in that 30-by-30 chunk of the world, the tallest object tops out at 4,500 feet. Cross that box at or above 4,500 and you will clear everything in it - every peak, every tower, and every guy wire holding those towers up.

Is the MEF a Minimum Safe Altitude?

No - and this is the single most misunderstood fact about the number. The MEF is not a floor and it is not the altitude you’re allowed to fly. It is a statement of fact about the tallest object in the box, nothing more.

If you fly exactly at the MEF, you are theoretically level with the top of the tallest obstacle. You are not clearing it by a comfortable margin - you could be scraping right over the top of a tower with almost nothing to spare.

Think of the MEF as a reference. It is the number you build a safe altitude on top of. Turning that reference into a real cruising altitude with margin baked in is the entire purpose of cross-country planning.

How Is the MEF Calculated?

Knowing how the number is built tells you exactly how much to trust it.

The chart makers start with the highest known feature in the quadrangle. Say the tallest peak measures 3,860 feet. They then add a buffer - often a couple hundred feet - to account for imperfect surveys, vertical error in the source terrain data, and obstacle tolerances. Finally, they round up to the next hundred.

So a 3,860-foot peak might become an MEF of 4,100 feet after the buffer and rounding.

The critical limitation: the MEF only accounts for known, charted obstacles. New construction, a crane parked at a work site for six months, or a skinny unlit meteorological (met) tower thrown up almost overnight in farm country may not be on the chart yet. The charting cycle takes time to catch up.

Treat the MEF as an excellent, authoritative starting point - not as a force field.

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

Here’s the practical workflow on a real cross-country. Suppose you’re flying from an airport on the plains toward higher ground to the west.

1. Read a corridor, not a line. Don’t just check the boxes your course line passes through - check the boxes on either side. A little uncorrected drift, a diversion around a cloud, and you can end up over the neighboring quadrangle. Scan a corridor at least 10 miles either side of course.

2. Read the MEFs box by box. You might see 2,100, then 2,400, then a jump to 5,300, then 6,200, then back down to 3,100. That spike tells you something tall is out there - a ridge, an isolated peak, or a tower farm on a hill - before you’ve even read the terrain colors.

3. Find the single highest MEF along the corridor. In this example, that’s 6,200 feet. Write it down on your nav log; it drives your altitude decision.

4. Add real margin. A good personal rule is at least 1,000 feet above the highest MEF in daytime, and more at night or over rough terrain. Above a 6,200-foot MEF, that puts your absolute floor at 7,200 feet.

5. Round up to a legal, comfortable altitude. Climbing to something like 8,500 feet gives you extra cushion and keeps you legal on the hemispheric rule - provided the airplane climbs there comfortably and the winds aloft cooperate.

That’s the whole game: you went from a blue number in a box to a cruising altitude with real terrain margin underneath you.

Why Does the MEF Matter More at Night?

At night over dark terrain, you cannot see the ridge you’re closing on or the unlit tower ahead. On a moonless night over the mountains, the first hint of rising terrain may be the stars disappearing at the bottom of your windshield.

That is exactly when the MEF earns its keep. Because you can’t verify terrain clearance with your eyes, you lean harder on the chart and give yourself more margin, not less.

If 1,000 feet feels fine in daylight, give yourself 2,000 feet at night in the hills. The number in the box doesn’t change - but the cushion you stack on top of it absolutely should.

MEF vs. OROCA vs. MSA: What’s the Difference?

These get confused often, so here’s the cleanup.

MEF vs. OROCA. The Off-Route Obstruction Clearance Altitude (OROCA) on IFR low-altitude charts is a cousin of the MEF, but it bakes in a bigger buffer - 1,000 feet in non-mountainous areas and 2,000 feet in mountainous areas - so it’s closer to a ready-to-fly safe altitude. The MEF is barer: raw obstacle top plus a small survey buffer, with the margin left as your job.

MEF vs. MSA/MVA. The MEF is also not a Minimum Safe Altitude or the Minimum Vectoring Altitude a controller uses. Those are different tools for different jobs. On your VFR sectional, day or night, the MEF is your terrain conscience.

What Does the Checkride Examiner Want to See?

The Airman Certification Standards (ACS) for cross-country planning expect you to compute and select a cruising altitude that accounts for terrain and obstruction clearance. That word - terrain - is right there in the standards.

The examiner wants a candidate who can put a finger on the chart, read the MEFs along the route, identify the highest one, and explain the altitude choice.

Say it out loud like this: “My highest Maximum Elevation Figure along this corridor is 6,200, so I selected a cruising altitude of 8,500 to give myself margin over terrain and stay legal for my direction of flight.” That connects the chart to a decision, which is exactly what the examiner came to see.

What you don’t want is to draw a beautiful magenta course line and never look at the terrain it crosses - planning a route while forgetting the third dimension.

Key Takeaways

• The MEF is a reference, not a floor. It marks the top of the tallest known object in a 30-by-30-minute quadrangle, plus a small buffer, rounded up - fly above it, never at it.
• Read MEFs as a corridor, at least 10 miles either side of course, and write down the single highest one on your nav log.
• Add margin on top: 1,000 feet by day, 2,000 or more at night or over mountains, then round up to a legal cruising altitude.
• The MEF only covers charted obstacles - check NOTAMs for new towers, cranes, and temporary structures the chart hasn’t caught yet.
• When a lowering ceiling squeezes the gap between the clouds and the MEF, the chart is telling you to turn around or land - not to press on into rising terrain.