What is MEF in Aviation? (Maximum Elevation Figure)

In the world of aviation, safety is of utmost importance. Pilots and air traffic controllers rely on precise data and information to ensure the smooth operation of air traffic. One crucial piece of information that plays a vital role in flight planning and navigation is the Maximum Elevation Figure (MEF).

The MEF is a critical value that represents the highest terrain or obstacle within a defined area. It is expressed in feet above mean sea level and provides a safety buffer for aircraft flying at lower altitudes.

But what exactly does the MEF mean in aviation, and how is it determined?

Understanding the Maximum Elevation Figure (MEF)

The Maximum Elevation Figure (MEF) is a value used to highlight the highest terrain or obstacle within a specific area. It ensures that pilots have the necessary altitude clearance to navigate safely. The MEF is particularly crucial for visual flight rules (VFR) operations, where pilots rely on their visual observations to navigate rather than relying solely on instruments.

The MEF is determined by surveying and mapping agencies and is usually represented in sectional charts or aeronautical charts. These charts provide essential information to pilots about the features and hazards they might encounter during their flight.

For example, a sectional chart might indicate an MEF of 2,000 feet for a particular area. This means that the highest terrain or obstacle within that area is 2,000 feet above mean sea level. Pilots planning a flight in this area need to ensure that their assigned altitude is above this value to maintain safe clearance.

It’s important to note that the MEF does not account for the presence of man-made structures such as buildings, towers, or antennas. These structures are typically charted separately and included in the documentation provided to pilots.

The MEF is a valuable tool for flight planning and helps pilots make informed decisions about the altitudes at which they can safely navigate. By incorporating the MEF into their flight planning process, pilots can mitigate the risk of flying too low and potentially colliding with terrain or obstacles.

Factors Affecting the Maximum Elevation Figure (MEF)

Several factors are taken into consideration when determining the Maximum Elevation Figure (MEF) for a specific area. Understanding these factors can shed light on how the MEF is calculated and the accuracy of the provided values.

Terrain and Topographical Features

The terrain and topographical features in a given area heavily influence the MEF. Steep mountains, deep valleys, and other natural formations can significantly impact the MEF value. Locations with rugged terrain may have higher MEF values to ensure proper clearance for aircraft.

Additionally, the presence of bodies of water, such as lakes or rivers, also affects the MEF. Water bodies may have a lower MEF to account for the altitude of the surface of the water.

Airspace Classification

The classification of airspace also plays a role in determining the MEF. Different types of airspace have varying requirements for altitude clearance to ensure safety. Controlled airspace, such as Class B or C airspace, often requires higher MEF values to account for the presence of commercial airports, busy traffic, and strict air traffic control.

On the other hand, uncontrolled airspace, such as Class G airspace, may have lower MEF values as there are typically fewer restrictions and lower air traffic density.

Obstacle Clearance Requirements

The specific obstacle clearance requirements also contribute to the determination of the MEF. Certain areas may have higher MEF values to account for obstacles such as tall buildings, transmission towers, or wind turbines that need to be avoided during flight.

These obstacles are often marked on aeronautical charts and are accompanied by their respective heights above mean sea level. Pilots must consider both the MEF and these obstacle heights when planning their flight to ensure safe passage.

By considering these factors, surveying and mapping agencies can calculate the MEF for specific areas and provide pilots with accurate and up-to-date information to assist them in their flight planning and navigation.

The Importance of the Maximum Elevation Figure (MEF)

The Maximum Elevation Figure (MEF) plays a crucial role in aviation safety and flight planning. It ensures that pilots have the necessary altitude clearance to navigate safely and avoid potential hazards.

Here are a few key reasons why the MEF is essential:

Terrain Avoidance

The MEF helps pilots avoid collisions with terrain or obstacles during flight. By providing a minimum safe altitude, pilots can ensure they maintain sufficient vertical separation from the ground or any potential obstructions.

Pilots can use the MEF to determine the minimum altitude at which they can safely fly in a particular area. This ensures that they have enough clearance between their aircraft and the highest point of the terrain or obstacle.

Flight Planning

The MEF is an essential factor in flight planning. By incorporating the MEF into their calculations, pilots can choose appropriate altitudes and flight routes to ensure safe passage.

During the flight planning process, pilots consider various factors such as weather conditions, airspace restrictions, and terrain characteristics. By accounting for the MEF, pilots can make informed decisions and choose altitudes that provide adequate clearance from obstacles.

Traffic Separation

The MEF also helps regulate traffic separation. By defining the minimum safe altitude within a specific area, the MEF ensures that aircraft flying at lower altitudes can navigate safely without interfering with other traffic.

Pilots can understand the altitude restrictions imposed by the MEF and maintain the appropriate vertical separation. This coordination of altitudes enhances air traffic management and reduces the risk of potential collisions.

In conclusion, the Maximum Elevation Figure (MEF) provides critical information for pilots, aiding their flight planning and ensuring safe navigation. By accounting for the MEF, pilots can avoid potential collisions with terrain or obstacles, make informed decisions during flight planning, and maintain proper traffic separation. The MEF serves as a valuable tool in aviation safety and contributes to the overall efficiency and smoothness of air traffic operations.


1. Federal Aviation Administration (FAA). “Frequently Asked Questions – Aeronautical Information,” FAA.

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