What is the difference between AGL and MSL?

Question

I'm a student pilot, and in ground school we are learning about airspace and all that good suff. Though, I can't undertsand what agl and msl is. I know msl is mean sea level and agl is above ground level. Someone else asked this question on yahoo, I read the answer, and I still don't get it.

I know asl is above sea level and I know what msl means too. I just don't undertsand the concept. None of it makes sence. I don't understnad how you could have different altitudes, and is you know your msl how do you find out your agl?

Answer 1

When referring to an altitude of an aircraft or airspace MSL is used. You get MSL from your altimeter and ATC sees your altitude in MSL (Your altitude above Sea Level)

To find out your approx AGL you would take the elevation of your closest airport for expample and substract it from the altitude on your altimeter (MSL)
- Some aircraft have radar altimeters on board and are able to tell exactly what their AGL altitude is- For the most part you only need to worry about MSL.

Lets say you are departing from an airport with a field elevation of 1,000 ft - If you are in the aircraft on the ground your altimeter should read 1000ft. Lets say you take off ond you are flying along. Your altimeter reads 2,000 FT .. You are now 1,000 FT AGL

Hope this helps

Answer 2

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RE:
What is the difference between AGL and MSL?
I'm a student pilot, and in ground school we are learning about airspace and all that good suff. Though, I can't undertsand what agl and msl is. I know msl is mean sea level and agl is above ground level. Someone else asked this question on yahoo, I read the answer, and I still don't...

Answer 3

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 4

AGL stands for Above Ground Level and is the difference between the altitude of the ground and the sea altitude which is zero.
An example can be, you are flying at 2000 feet above sea level, however your AGL might be 1500, if the ground under you has an elevation of 500ft. in other words msl means altitude above the sea which is always zero, and AGL means altitude above the ground, which depends on the elevation where you are at.

Answer 5

MSL means how high you are above sea level, the actual ocean if you will. AGL means the ground under you. If you're flying around Houston, for example, MSL and AGL are about the same. Over Denver, however, when you're sitting on the ground you're at about 5,000 MSL, but 0 feet AGL. Does that help?

Answer 6

MSL, or mean sea level, is the altitude above sea level. Since AGL, or above ground level, changes as you go over differing terrain, we use MSL to set our altimeter so we are on a common measurement. For instance, where I live, in the Willamette Valley of Oregon, our elevation is only about 200' above sea level. If I am at 1200' msl in the pattern at my airport, I am 1000' agl. Think of agl as msl minus the current terrain elevation. HTH

AGL has to be computed. If you look ar your airport info (like the flight guide) it tells you the airport elevation (mine is 210'). We usually don't know the elevation everywhere we are flying over, so we use MSl unless we have restriction that say we have to stay, say 2200' above someplace (like a wildlife refuge) then you can gusss that the airport is 200' then I better stay 2200' msl in that area.

Email me if you need more help.

Answer 7

Msl Altitude

Answer 8

Wikipedia gives a reasonable definition of AGL that refers to MSL.

In aviation, Above Ground Level (AGL) denotes that a given altitude is measured above the ground, rather than above sea level (ASL). It is important for aviators to differentiate between AGL and an altitude given ASL as the two could be very different in mountainous terrain. Over the ocean, altitude AGL and ASL will be identical. http://en.wikipedia.org/wiki/Above_ground_level

If my memory serves me right MSL is a Barometric, Pressure, related measurement. It establishes Altitude by pressure. AGL requires radar to determine.

Run this by your instructor but I believe if you zero your altimeter you'll read the true barometric pressure, given accurate calibration. Where as if you enter the barometric pressure you'll read MSL of your field given temperature and pressure of that moment.

Answer 9

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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 10

AGL=Above Ground Level
MSL=Mean Sea Level
ASL=Above Sea Level