Not to beat this dead horse any deader, but folks who learn to fly where
this knowledge is important, such as Canada, Alaska, New Zealand, etc, get
it as part of their training. I'm chauvinist enough to think that the
majority of participants in this ng do not fly in those areas, and thus a
general question to the group won't get many enlightened responses. I
learned to fly in Southeast Alaska, and never heard the word subsidence
mentioned.

Bob Gardner

"private" wrote in message
news:5kgve.1798330$6l.939730@pd7tw2no...

"Peter Duniho" wrote in message
...
"private" wrote in message
news:3Q6ve.1795956$6l.1699114@pd7tw2no...
[snip]

None of what you wrote suggests that atmospheric subsidence would have
any
significant effect on the aerodynamics or engine of an airplane.

It is true that there are variety of atmospheric effects related to
nightfall. But they don't change the way the airplane flies, not in a
way
that requires even knowing about atmospheric subsidence, never mind
understanding it.

Pete

Hello Pete,

I agree that subsidence does not change aircraft aerodynamics, and does
not
have a significant effect on engine power. What it does do is change the
way an aircraft performs. Rising air adds to an aircraft's climb rate,
sinking air subtracts from it. There will be small changes in maximum
level
cruise speed and aircraft attitude with respect to horizon when flying in
descending air.

IMHO it is better to have unrequired knowledge than to be in ignorance
when
that knowledge is needed. My main instructor always maintained that you
can
never have too much weather knowledge.

There is some discussion of subsidence and katabatic and glacier fed
downslope winds in this excellent BC weather manual from Navcan. There is
also discussion of coastal diurnal and wintertime outflows.
http://www.navcanada.ca/ContentDefin...k/bc/BC31E-V.P
DF
Note chapter 2 Aviation Weather Hazards, page 28 provides discussion of
glacier winds and notes local wind speeds to 80 knots and notes that
these
winds may be magnified by terrain funneling and comments that they may be
pulsing in a kind of reverse thermal. I would submit that this subsidence
is substantial and hardly "irrelevant from a practical standpoint."

This subsidence can add to the reduction of performance due to density
altitude and is often a factor in failure to climb after takeoff or
inability to out climb rising terrain and has contributed to lots of
crumpled aluminum in the mountains.

Just my .02