Understanding altitude is paramount for safe and efficient flight. A frequent question among pilots, especially those new to aviation, is “Are Sectional Charts Msl Or Agl?” The answer is crucial for interpreting these vital navigational tools correctly and maintaining appropriate terrain clearance.
Sectional Charts and the Mystery of Altitude Are Sectional Charts Msl Or Agl
Sectional charts, the primary navigational charts used by pilots in the United States, depict altitudes in Mean Sea Level (MSL). This means that the altitudes of terrain, obstructions (like towers and antennas), and airports are referenced to the average height of the sea. Knowing that Sectional Charts use MSL for altitude representation is fundamental for flight planning and situational awareness. This is how sectional charts work:
- Terrain elevation is shown in brown contour lines, with numbers indicating the MSL altitude of those lines.
- Obstructions are marked with their height above ground level (AGL) and their MSL altitude (AGL/MSL). For example, “345 (456)” next to a tower means the tower is 345 feet above the ground and 456 feet MSL.
- Airport elevations are also given in MSL on the airport information.
Above Ground Level (AGL), on the other hand, refers to the height above the terrain directly beneath the aircraft. AGL is dynamic, changing as the aircraft flies over varying terrain elevations. While sectional charts predominantly use MSL, understanding AGL is equally important. Pilots calculate AGL altitude by subtracting the terrain elevation (MSL) from their aircraft’s altitude (MSL). Therefore, knowing the MSL altitude from the sectional chart and comparing it to your altimeter setting allows for the determination of AGL, which helps ensure safe clearance from obstacles and terrain.
Consider the following table which summarizes the difference between MSL and AGL in context of sectional charts:
| Term | Definition | Use on Sectional Charts |
|---|---|---|
| MSL (Mean Sea Level) | Altitude referenced to the average sea level. | Used for terrain elevation, airport elevation, and the MSL altitude of obstructions. |
| AGL (Above Ground Level) | Height above the terrain directly beneath the aircraft. | Shown for obstruction height, and calculated by the pilot to determine terrain clearance. |
For even more detailed information and to enhance your understanding of sectional charts, consult the official FAA Aeronautical Chart User’s Guide. The document thoroughly explains how to interpret all aspects of these charts and provides invaluable information for pilots of all experience levels.