What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

NOTAM/TFR Question: Why are altitudes not always puiblished in MSL?

David_Nelson

Well Known Member
What utility is there in publishing a NOTAM/TFR in AGL? Below is a random sampling from across the country and I can find no rhyme nor reason as to why some are published in AGL and others in MSL. Do you know why?

FDC 2/8960: San Angelo, Texas near SAN ANGELO VORTAC (SJT) - From and including 3500 feet MSL up to but not including 18000 feet MSL

FDC 2/7233: McGregor, Texas near TEMPLE VOR/DME (TPL) - From the surface up to and including 2000 feet AGL

FDC 2/2186: FRANKLIN, Illinois near SPINNER VORTAC (SPI) - From the surface up to and including 2000 feet AGL

FDC 2/0955: Grand Forks AFB, North Dakota - From the surface up to and including 2400 feet MSL
 
7930.2

FAA Order 7930.2 Chapter 7 allows for the use of either MSL or AGL. As for the AGL vs MSL, depends on the operation. They may need exactly 2000’ of separation. Terrain may vary over a wide area. If the average elevation was say 221’ and they wanted 2000’ of separation, they don’t issue SFC to 2221’ MSL. It would not achieve the 2000’ due to terrain variance and not within the level of precision assumed for aircraft equipment read outs (round dial resolution and other altimeter errors) They instead issue SFC-2000 AGL.

There are lots of other reasons.
 
FDC 2/7233: McGregor, Texas near TEMPLE VOR/DME (TPL) - From the surface up to and including 2000 feet AGL

This one is a SpaceX facility - complete with launch gantry that I suspect is for rocket motor testing. Perhaps 2000' is the blast zone :)
 
Back
Top