What is the Maximum Elevation Figure (MEF) on a sectional chart?

The Maximum Elevation Figure (MEF) is a large blue number printed in each latitude/longitude quadrangle on a sectional aeronautical chart, representing the highest known elevation of terrain or obstacles within that quadrangle. It is expressed in hundreds of feet MSL — for example, a figure of 52 means 5,200 feet MSL. The FAA adds a buffer to the actual highest feature to account for potential uncharted obstacles, giving pilots a conservative reference for terrain and obstacle clearance.

How do you read and use the MEF on a sectional chart for flight planning?

To use the MEF, locate the quadrangle (bounded by tick marks at each 30 minutes of latitude and longitude) that covers your planned route, then read the blue bold digits printed in that square and multiply by 100 to get the altitude in feet MSL. Pilots and remote pilots use this figure to quickly determine a minimum safe altitude that clears the highest terrain or obstacle in the area. The Pilot's Handbook of Aeronautical Knowledge (PHAK) recommends cross-referencing the MEF with other chart symbols to build a complete picture of airspace hazards along a route.

What's the difference between the MEF and the Maximum Authorized Altitude (MAA) on a sectional chart?

The MEF represents the highest terrain or obstacle elevation within a quadrangle and is used for terrain and obstacle avoidance during flight planning, while the Maximum Authorized Altitude (MAA) is an off-route altitude published on IFR en route charts indicating the highest usable altitude that ensures acceptable navigation signal coverage for a given airway. These two values serve entirely different purposes: the MEF is a terrain-clearance reference found on VFR sectional charts, whereas the MAA is an IFR airway limitation found on IFR en route low-altitude charts. Confusing the two could lead to a serious misunderstanding of airspace constraints.

Maximum Elevation Figure (MEF) on Sectional Charts

When you unfold a VFR sectional chart — whether you're a manned-aircraft pilot or a Part 107 remote pilot-in-command — one of the most immediately useful pieces of information printed across the surface is a series of large blue numbers arranged in a grid-like pattern over the land. These are Maximum Elevation Figures (MEFs), and understanding them is essential for anyone operating in the National Airspace System. For sUAS (small unmanned aircraft systems) operators flying under 14 CFR Part 107, MEFs serve as a quick-reference tool for identifying terrain and obstacle hazards that could lie in the flight path of a drone — potentially at altitudes well below the 400-foot AGL ceiling that governs most recreational and commercial unmanned operations.

MEFs appear throughout the low-altitude airspace environment that drone pilots inhabit every single flight. Learning to read, interpret, and apply MEF data is not just a knowledge-test requirement — it is a fundamental habit of aeronautical decision-making that can prevent a costly or dangerous collision with terrain, towers, or other structures.

What Is a Maximum Elevation Figure?

A Maximum Elevation Figure is a value printed on a VFR sectional chart that represents the highest obstacle or terrain elevation within a specific geographic quadrangle — a four-sided area bounded by lines of latitude and longitude, each measuring 30 minutes of latitude by 30 minutes of longitude. The FAA defines the MEF as the highest known feature in a quadrangle, with a buffer built in for safety.

The MEF is expressed in hundreds of feet above mean sea level (MSL). The large digit represents thousands of feet and the smaller raised digit represents hundreds. So an MEF reading of 2 5 means the figure is 2,500 feet MSL. An MEF of 1 2 means 1,200 feet MSL. Some MEFs will be a single small digit, such as 0 9, representing 900 feet MSL. This notation can trip up students who are not used to seeing figures expressed this way, so study the format carefully.

How MEFs Are Calculated

The FAA does not simply take the tallest charted object in a quadrangle and print that number. Instead, there is a standardized methodology designed to add a safety margin. According to the Aeronautical Chart User's Guide, the MEF is determined by:

Identifying the highest terrain or obstacle in the quadrangle — this could be a mountain peak, a hilltop, a radio tower, a wind turbine, a building, or any other charted vertical obstruction.
Adding a vertical buffer: For terrain, the chart compilers round up to the nearest 100 feet and add 200 feet of clearance. For man-made obstacles, they round up to the nearest 100 feet and add 300 feet to account for any uncharted obstacles (such as supporting guy wires, which can extend horizontally from a tower and have their own vertical height) or obstacles that may have been constructed since the chart was last revised.
The resulting figure is the MEF printed on the chart.

This methodology is critically important for drone pilots to internalize: the MEF is not just the height of the tallest tower or hill — it already incorporates a safety buffer. However, that buffer was designed with manned aircraft in mind, and the values are in MSL, not AGL. A remote pilot must mentally convert the MSL MEF to an AGL value at the specific operating location to determine what the figure actually means at ground level.

MEFs Versus AGL: A Critical Distinction for Part 107 Operators

This is the most practically important concept for drone pilots to master. Part 107 operations are typically governed by a 400-foot AGL ceiling unless operating within 400 feet of a structure. MEF values are given in MSL. To use a MEF meaningfully, you must know the elevation of the ground at your launch site and along your flight path.

Consider a practical example: You are planning a drone flight over farmland in the Midwest. The MEF printed on the sectional for that quadrangle reads 1 4, or 1,400 feet MSL. Your launch point sits at a field elevation of 1,100 feet MSL. That means the MEF represents an obstacle or terrain feature reaching to roughly 300 feet AGL from your location — well within the operational envelope of a Part 107 drone flight. You now know that there may be obstacles up to about 300 feet above your launch elevation somewhere in that quadrangle. Your 400-foot AGL ceiling would put your drone at 1,500 feet MSL — 100 feet above the MEF — leaving a thin margin. You should investigate further using aeronautical charts, digital obstacle files, or other resources to identify what specific obstacle accounts for that MEF before flying.

Contrast this with a flight in a mountainous area where your launch pad sits at 4,000 feet MSL but the MEF for the quadrangle is 8,500 feet MSL. In that case, higher terrain or obstacles elsewhere in the quadrangle — potentially miles away — are driving the MEF figure. The MEF alone cannot tell you whether your specific flight path is clear, only that somewhere in the quadrangle there is terrain or an obstacle reaching to that elevation.

Why MEFs Matter to Remote Pilots

Part 107 remote pilots are required to know and apply sectional chart symbology as part of their aeronautical knowledge. MEFs are directly relevant for several real-world operational reasons:

Pre-flight hazard assessment: Before any flight, a remote pilot must assess the airspace and terrain. MEFs provide an immediate, chart-readable snapshot of the highest potential obstacle in the area, saving time during preflight planning.
Identifying tall obstacle zones: A sudden jump in MEF values between neighboring quadrangles — say, from 0 9 to 2 7 — signals a dramatic change in terrain or the presence of a significant obstacle like a communications tower. That contrast on the chart is a visual cue to investigate further.
Comparing to your operational altitude: If your intended cruise altitude (in MSL) would be below the MEF for the quadrangle, you have a clear signal that obstacles or terrain within that area may present a collision hazard and you need to revise your plan.
Situational awareness for BVLOS concepts: Even for standard visual line-of-sight operations, understanding the three-dimensional obstacle environment makes you a safer, more professional operator.

Key Numbers and Rules

MEF values are in feet MSL — not AGL.
The MEF format on sectional charts uses a large digit for thousands and a small raised digit for hundreds of feet MSL.
MEFs include a safety buffer: approximately 200 feet added for terrain and 300 feet added for man-made obstacles, after rounding up to the nearest 100 feet.
Part 107 maximum altitude is generally 400 feet AGL (or 400 feet above a structure when within 400 feet of it).
MEF quadrangles are bounded by 30 minutes of latitude and 30 minutes of longitude.
The MEF reflects the highest known feature in the quadrangle — it does not indicate whether every part of the quadrangle has obstacles at that level.
Sectional charts are updated on a 6-month (semiannual) revision cycle; always use a current chart, as new towers and structures are added regularly.

Common Test Traps

Confusing MSL and AGL: The FAA knowledge test loves to present an MEF and ask whether a given drone altitude is safe, expecting you to account for terrain elevation and convert properly. Always identify your local ground elevation before drawing conclusions from an MEF.
Misreading the digit format: Students often misread the large/small digit combination. A large 1 with a small raised 2 is 1,200 feet MSL — not 12,000 and not 120. Practice reading several MEFs on a sample chart until the format is automatic.
Assuming the MEF clears your entire route: The MEF is the highest feature somewhere in the quadrangle. It tells you the maximum height of concern, not the location. Your specific flight path could still have obstacles that account for most or all of the MEF value concentrated near your route.
Forgetting the safety buffer is already included: The MEF is not the raw height of the tallest object — it has a buffer already baked in. Do not add another 200 or 300 feet on top when doing altitude calculations; the buffer is there to account for uncharted hazards, not to serve as an extra operating margin for your drone.
Using an outdated chart: New communications towers, wind turbines, and other structures are erected constantly. An MEF on an out-of-date chart may not reflect recently built obstacles. Always verify currency and supplement chart data with FAA digital obstacle files or apps that pull from current FAA sources.

Mastering the MEF is one of the foundational skills of sectional chart literacy for Part 107 pilots. It provides a rapid, reliable method for gauging the obstacle and terrain environment before you ever launch a drone, and it connects the paper (or digital) chart directly to the three-dimensional world your aircraft will occupy. Make reading MEFs a reflex during every preflight planning session, and you will be both a more prepared test-taker and a safer operator in the field.