Can someone explain the difference between MSL and AGL in a simple way for me to understand?

Question

I can't get a grip on the difference between AGL(above ground level) and MSL(mean sea level). Can anyone explain it and tell me an easy way to figure it out?

Answer 1

now that this poor chap has become totally confused allow me an attempt, MSL is the published elevation of the airport above sea level, for instance if the published airport elevation is 560 then your altimeter ( used to determine your altitude while flying ) will if calibrated correctly read 560 when the altimeter is set to the correct current barometric pressure. Standard pressure is considered 29.92. As pressure variations exist over broad areas, this setting is updated from time to time to ensure that you are getting a correct reading now read as altitude above MSL. AGL is the difference between the MSL displayed altitude and the actual terrain elevation. In a hypothetical situation if you are flying at an altitude of 5,000 feet MSL over terrain that rises from say 600 feet MSL to say 3,000 feet MSL then you can see that your actual altitude AGL will become lower as you fly into rising terrain. Aeronautical charts (low level) will show obstacles heights such as radio towers as above ground level. Aircraft flying above 18,000 feet msl use the standard 29.92 altimeter setting for the portion of flight at or above 18,000 feet. Most airports have a sensitive altimeter and can tell you the current barometric pressure, if that information is unavailable the pilot sets the altimeter to the known field elevation and reads the corresponding pressure. This information along with temperature is important in calculating aircraft performance from tables and graphs which are derived from standard 29.92 inches 59 degrees f. enroute aircraft obtain updated altimeter settings from ground stations in close proximity to their position. As you can see AGL altitude varies constantly as the aircraft proceeds on course therefore the only constant is MSL which is important information when working in and around controlled airspace or providing traffic separation clearance enroute. I know it's not the simplest of explanations, but it is important the you understand the relevance especially if you are learning to fly. Have your instructor spend some time with you utilizing a sectional chart.

Answer 2

AGL: since the ground you stand on isn't limited to being a sidewalk, but can be in the form of a mountain, plateau, or any high elevation, or even a depression such as a meteor crater, or canyon, it is still the ground. When you are in an aircraft above that area, your above ground level altitude will be the distance between your aircraft and that particular ground level. MSL: is the level of ocean water. When your aircraft is above the ocean/sea, the MSL is the distance between the water and the craft you are in. Sometimes the sea level is higher than the ground level. Some examples would be New Orleans, the Netherlands, the Dead Sea. More times than not, the MSL is Lower than the AGL.

Answer 3

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RE:
Can someone explain the difference between MSL and AGL in a simple way for me to understand?
I can't get a grip on the difference between AGL(above ground level) and MSL(mean sea level). Can anyone explain it and tell me an easy way to figure it out?

Answer 4

Lets say you are standing on a piece of land and was told that it is 50 feet elevation (also know as 50 feet ASL). That means the piece of land is above the sea level of 50 feet. Then lets say you have a tree besides you that is 20 feet tall and you climb up to the top of the tree, you are now 20 feet AGL and also equal to 70 feet MSL. So, to find out what is the AGL when you are flying at a particular location, you would need to know what is the Elevation (always stated on the map) on that location and then minus off your altitude you are flying at will give you the AGL.

Answer 5

atcaugh85 got it almost right.

MSL = Mean Sea Level, ie, at the beach midway between high tide and low tide
ASL = Above Sea Level
AGL = Above Ground Level

In aviation, the difference between high tide and low tide is negligible, unlike a boat, which, for example, may only be able to enter a harbour at high tide. That is why in aviation we drop the "M" in ASL. An altimeter set to the correct barometric pressure will give the height of an aircraft ASL. All aircraft position reporting and airport elevations in ICAO countries are in feet ASL. If you are flying over land that is higher than sea level, for example over mountains, then you also need to know the AGL, or height Above Ground Level. The only way to know this is by subtracting the altitude ASL from the actual ground level, or with a radar altimeter. So an aircraft sitting on the ground at an airport 3000 feet ASL will show 3000 feet ASL on its altimeter, and if it is flying 1000 feet above that airport the altimeter will show 4000 feet.

The International Civil Aviation Organization (ICAO) standard for measuring ASL is feet.

Answer 6

Is this a joke or what? AGL and MSL had better not be confused or somebody is going to die!

They are not related, except if you are crashing in the ocean (or maybe you've got a float plane). As explained above, MSL is sea level, and AGL is altitude above ground level. Ground level varies, see above comments on mountains and valleys. Most VFR aircraft have no way of "knowing" what their height AGL is, so we always refer to altitude ASL, yet another term, but at least it is constant.

Answer 7

MSL is the number the altimeter shows when you hit the tower. AGL is how far you fall to the ground.

Answer 8

Above Ground Level

Answer 9

You're standing on top of a 10,000 foot high mountain. You are at 10,000' MSL, and 0' AGL.

Got it now?

Answer 10

I think the dude above me sumed it up. Think about the words. MSL(mean sea level) where are you in reference to the sea/ocean. ASL, how far above the ground are you.
Happy flying.