Are you a recreational drone enthusiast or a professional commercial pilot? Whether you're flying a recreational drone, a commercial drone, or a manned aircraft, altitudes above ground level (AGL) and mean sea level (MSL) are crucial parameters.
For drone pilots, correctly understanding the differences and similarities between AGL and MSL is crucial. Ensure every flight is safe and compliant!
What are AGL and MSL?
AGL (Above Ground Level) and MSL (Mean Sea Level) are technical terms used in drone flight altitudes. Misunderstanding these terms can lead to violations, crashes, and even endangering manned aircraft.
What is AGL?
AGL (Above Ground Level): This is the height of your drone above the ground directly below it.
If you're hovering 100 feet above a mountain, that's 100 feet of AGL (Above Ground Level). This is a dynamic measurement that changes as the terrain changes.
This means that as you fly over a valley, your AGL will increase, even if your drone's altitude remains constant. AGL (Above Ground Level) has nothing to do with the height of the terrain you're currently flying; it only indicates the altitude above the ground. Also, keep in mind that the FAA and most countries' civil aviation regulations generally limit drones to 400 feet AGL.
What is MSL?
MSL (Mean Sea Level): This is the altitude of your drone relative to the global mean sea level.
If you're flying at an altitude of 5,000 feet and ascend 300 feet AGL, your drone's actual altitude is 5,300 feet MSL, regardless of the terrain below.
MSL is a fixed reference altitude used in aeronautical charts, airspace layers, and air traffic control (ATC). MSL data is particularly important when drones need to share airspace with manned aircraft.
AGL vs. MSL: What's the difference?
AGL measures the altitude above the ground below you, while MSL measures the altitude above sea level. Due to varying terrain, MSL is often higher than AGL (for example, if you are flying at 5,280 feet above sea level and 100 feet above sea level, your altitude is 5,380 feet above sea level).
AGL is often limited to a 400-foot limit, with the ground as the reference point, and the altitude is dynamic. MSL is a fixed altitude relative to sea level and is commonly used in aeronautical charts, airspace demarcation, and air traffic control communications.
Why Drone Pilots Need to Know the Difference Between AGL and MSL?
Understanding AGL and MSL is crucial for safe drone operation, especially for pilots operating under US Part 107 regulations and remotely operated drones.
Compliance
FAA Part 107 requires that drones must not exceed a maximum flight altitude of 400 feet AGL.
If you are flying in mountainous areas or high altitude areas, you need to be aware of the actual MSL to avoid entering the path of manned aircraft.
The Federal Aviation Administration (FAA) limits most drones to 400 feet above sea level (AGL) in uncontrolled airspace (Class G) to avoid conflicts with manned aircraft.
If you're flying in mountainous or high-altitude areas, you also need to be aware of your actual MSL altitude to avoid entering the path of manned aircraft.
Airspace Safety
Airspace boundaries (such as Class B and Class E airspace) are often defined in terms of MSL.
Drone pilots must understand their altitude above MSL to avoid conflicts with manned aircraft, control towers, trees, or buildings.
METARs and TAFs report cloud heights in AGL, which is crucial for drone pilots to maintain a 500-foot buffer zone below the clouds. For example, if the cloud layer is at 1000 feet AGL, you must remain below 500 feet AGL, not mean sea level (MSL).
Mission Requirements
Mapping, geological exploration, energy inspections, and other missions often require AGL (Above Ground Level) data.
However, MSL data remains crucial for flight planning and cross-regional operations. For example, Autel industrial drones can perform waypoint, rectangular, and polygonal missions. When executing automated waypoint missions, it is crucial to ensure both the AGL and MSL altitudes for each waypoint to avoid collisions.
How to Properly Apply AGL and MSL During Flight?
For recreational and commercial drone pilots, the purpose of drone flight differs, leading to a more distinct distinction between AGL and MSL.
It's common for drone novice pilots to mistake AGL for MSL. This isn't true. MSL = AGL + Ground Elevation, or AGL = MSL - Ground Elevation. Focusing solely on one altitude during flight can lead to dangerous maneuvers.
In addition, a drone's radar altimeter provides real-time AGL readings, while the barometric altimeter displays MSL. A drone's barometer may be affected by weather, and AGL readings may vary. Verify these readings with maps and flight control data.
It's important to note that when taking off from the ground, the remote controller displays an AGL of 0 feet above ground level. As you ascend, you must set waypoint altitudes based on the MSL, as all waypoints are relative to your takeoff point. Setting waypoints at a uniform altitude is highly likely to result in a collision.
Before flight planning
Check the minimum sea level (MSL) of the flight area, especially when near airports or mountainous areas.
Check aeronautical charts to confirm airspace boundaries and manned aircraft routes.
During flight
Adhere to AGL restrictions (usually ≤400 feet). If you are operating a regulated commercial flight, you can apply for an altitude exemption.
When necessary, refer to the MSL displayed by the drone software or third-party tools.
Post-flight
Record AGL and MSL data for easier analysis of mission results.
Summary
AGL and MSL reflect the flight altitude of a drone under different flight conditions. AGL determines drone regulatory compliance and mission safety, while MSL determines aeronautical charts and airspace demarcation.
Whether you're shooting video with the Autel EVO II Pro V3 or conducting nighttime rescues with the Autel EVO Max 4N, always check ground elevation, read flight charts, and use a flight app to ensure legal flight. Choose your favorite drone model from the Autelpilot UAV Drone Store and fly freely!
