AGL and MGL - Flight altitudes and differences

So that not every pilot can decide for themselves how low they want to fly, there are standardized minimum flight altitudes in Europe. This MSA is measured by AGL.

AGL

In aviation, the abbreviation AGL stands for above ground level. This refers to the height above ground, i.e. the distance from the ground to the flying object.

In addition to AGL, there is also MSL. It indicates how high the flying object flies above the water.

MSA

The MSA is the required minimum flight altitude above the ground. The minimum flight altitude must be maintained for reasons of flight safety and the protection of persons and noise.

To this end, SERA has defined various minimum flight altitudes for European airspace. An MSA of at least 300m above the highest obstacle within a radius of 600m therefore applies above densely populated areas and gatherings of people. In all other cases, an AGL of at least 150m applies.

These rules apply both in the special flight zones and in the normal flight zones. Logically, however, they do not apply when taking off and landing.

Radar altimeter

The AGL of larger aircraft is measured using a radar altimeter. An on-board radar device measures the exact altitude of an aircraft. Put simply, the radar emits short electromagnetic waves towards the ground. These are reflected on the ground and received again by the radar altimeter. The altitude of the flying object is calculated from the time from the radar to the ground and from the ground to the radar. However, this technology works on land and not on water.

The UAV DACH e.V. association has developed safety concepts for UAS operations. You can find them here.