On 02/27/07 15:06, Peter R. wrote:
Sam and others, I have about 1,100 hours now with about 700 of those flown
after getting my instrument rating in the US back in 2003. Since then I have
flown IFR almost twice per week.

On a web-based aviation forum there is a general disagreement of the terms DA
(decision altitude) versus DH (decision height) when talking about an ILS
approach.

For those approaches that have published altitude minimums (typically ILS CAT
I or CAT II in the US), I was taught that the point at which one would begin
the missed approach is the decision height, or DH. However, in that aviation
forum there are a few who insist that this point is called the decision
altitude, or DA, and that DH is not valid for aircraft not equipped with
radar altimeter.

I did note that the current Pilot/Controller's glossary defines both DA and
DH as the point at which a missed does begin on a precision approach, but the
DA definition also includes the note about it being an ICAO definition.

Is this a case of semantics? Are DA and DH interchangeable when discussing
the point at which a missed begins? Or is there a more important distinction
between the two and I was simply taught inadequately?


I was taught that for instrument charts, "Altitudes" refer to MSL altitudes
and "Heights" refer to height above the ground. This means that DA refers to
the MSL altitude where the decision is made.

I think I read in the Jeppesen materials (or maybe it was a Rod Machado book)
that this terminology is the direction where things are going, but not everyone
agrees with this (yet). For example, the NACO Terminal Procedures Publication
still uses DH.

If you look at the Jeppesen charts, they use DA(H) to indicate that
this is the Decision Altitude MSL, with the height above the ground
shown in parenthesis.

I don't know from whom you can get a definitive answer.

Hope that helps,

--
Mark Hansen, PP-ASEL, Instrument Airplane
Cal Aggie Flying Farmers
Sacramento, CA