0
$\begingroup$

ASFC is an acronym frequently seen in official European publications, e.g. used by the French AIS:

enter image description here

Also in some ICAO ones, e.g in Annex 4 (Aeronautical Charts) to the Chicago Convention:

The airspace is shown only from the surface to the higher of the following two levels: 1500 m/above mean sea level (AMSL) — 600 m/above surface (ASFC).

What is ASFC compared to AGL? Is ASFC also used over water?

$\endgroup$
  • $\begingroup$ "Mean Sea Level" is an average altimeter setting based entirely on barometric pressure. If you took an airplane and flew it down to 0 over a calm open ocean, you may either be swimming or flying, so AMSL and ASFC are not technically the same over sea. Think about tides... I can't think why AGL and ASFC would be different though, other than AGL on maps usually the highest point in a specific area. $\endgroup$ – Ron Beyer Dec 28 '16 at 14:52
  • 2
    $\begingroup$ I've never heard of ASFC before, and it doesn't appear in any FAA materials. In fact, the only hits for it in Google are in French, where it's used as a synonym for AGL. Can you clarify where/why you've seen that ASFC and AGL are considered to be different things? Without that, it's hard to see what the actual question is here. $\endgroup$ – Pondlife Dec 28 '16 at 17:01
  • 1
    $\begingroup$ Like Pondlife says, it would be nice to see the source of your diagram. I have a database of all of the Glossary terms from FAA publications, the FARs, and miscellaneous sources. Of the 5379 terms, none of them are ASFC. $\endgroup$ – JScarry Dec 28 '16 at 17:18
  • $\begingroup$ Do you know what the letters are an abbreviation for in French? I’m wondering if this is referencing the geode? esri.com/news/arcuser/0703/geoid1of3.html $\endgroup$ – JScarry Dec 28 '16 at 20:30
  • $\begingroup$ @JScarry, French documents use the English wording only. It don't think the geoid is involved, the geoid doesn't perfectly match ground level, and for seas, it's below MSL (below the ellipsoid). $\endgroup$ – mins Dec 28 '16 at 20:37
5
$\begingroup$

As best I can tell, ASFC is only used in France and is synonymous with AGL.

First, it isn't in ICAO's list of abbreviations or the FAA's PCG, but it is in the French AIP in section GEN 2.2:

ASFC / Au dessus de la surface / Above surface

The AIP also lists AGL, but it doesn't explain the difference:

AGL / Au dessus du niveau du sol / Above ground level

Second, the AIP uses both terms in a seemingly interchangeable way. For example, in ENR 1.2 (VFR rules). Compare this from 4.7...

Come over the aerodrome, perpendicular to the runway at 2000 ft AGL, lights on, then join the circuit for landing

...with this from 4.10:

Fly over the runway at 2000 ft ASFC, perpendicular to the runway heading with landing lights switched on,

I can't see any reason why there would be any difference in meaning in those two phrases, and the airports in those sections are not particularly near the sea.

Finally, if you consider Wiktionary a valid reference, the definitions for ASFC and AGL are almost the same and they're both stated as the 'opposite' of MSL:

AFSC (Aviation) Désigne une hauteur au-dessus de la surface du sol ou de l'eau par opposition à une hauteur AMSL, dont la référence est le niveau moyen de la mer.

AGL (Militaire) Above ground level : « Au-dessus du niveau du sol », altitude relative au sol, par opposition à l’altitude absolue, mesurée par rapport au niveau de la mer.

Although this is a guess, I suspect that ASFC is simply an example of French phraseology that has now been superseded by English but hasn't been updated everywhere. I can't find ASFC used anywhere in a non-French context.

$\endgroup$
  • $\begingroup$ Please note that (as at January 2018) AFSC is still used on French 1:500 000 charts, most especially where it relates to the boundaries of military low-level flying corridors (AZBAs) and TMAs. It seems to be very much a French thing, but then, when in France ...... $\endgroup$ – Stephen Parker Jan 17 '18 at 15:15
  • $\begingroup$ @StephenParker You mean the "OACI" chart set? (also here) $\endgroup$ – mins Jan 17 '18 at 15:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.