"Mark Hansen" wrote in message
...
On 02/27/07 15:06, Peter R. wrote:

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.

In the TPP frontal matter, of course.

Landing minima are given as DA, decision altitude in feet MSL; RVR in 100's
of feet or whole and fraction statute mile; HAT (feet height above
threshold); and parenthetic equivalents for military. Circling minima
specify HAA (feet height above airport) rather than HAT. All four elements
are always present in NACO TPP landing minima.