Setting altimeters with no radio

"Peter Duniho" wrote in message ...
: "Jim Macklin" wrote in message
: ...
: they give altitude, accurate to within a few feet. just set
: the altimeter to read the same. then you know adjusted
: pressure. considering the legal requirements, it is
: perfectly adequate.
:
: First of all, no they don't give altitude accurate to within a few feet.
: Secondly, they give a completely different kind of altitude measurement than
: the altimeter provides. Even if the GPS were accurate to within feet for
: altitude, setting your altimeter to the GPS displayed altitude would not be
: the same as having the current, local altimeter setting.
:
: Pete
:
:

What about GPS precision approaches...where does the glideslope information come from?


WAAS?

".Blueskies." wrote in message
t...
What about GPS precision approaches...where does the glideslope
information come from?


WAAS?

WAAS is insufficient for a precision GPS approach. GPS precision approaches
use "LAAS", which is basically the same as WAAS except that the differential
station is much closer to the airport (I suppose in some or many cases it
may even be colocated...not sure). It's "local area" instead of "wide
area".

WAAS and LAAS are both a form of differential GPS, and it's true that both
increase the accuracy of GPS significantly, LAAS more so than WAAS.
However, a) Jim never restricted his claim to GPS using WAAS, and b) even
with WAAS (or LAAS, for that matter), the GPS does not indicate the same
altitude that a properly set altimeter would.

Pete

Peter Duniho wrote:

".Blueskies." wrote in message
t...
What about GPS precision approaches...where does the glideslope
information come from?


WAAS?

WAAS is insufficient for a precision GPS approach.

Nonsense. A fully deployed WAAS can provide precision GPS appoaches with
performance comparable to ILS (Cat 1).

GPS precision approaches
use "LAAS",

Not necessarily. In addition to WAAS, JPALS may be used in the future.

which is basically the same as WAAS except that the differential
station is much closer to the airport

LAAS transmits signals on the UHF band. WAAS does not. LAAS can eventually
provide more accuracy.

"Jessica Taylor" wrote in message
...
WAAS is insufficient for a precision GPS approach.

Nonsense. A fully deployed WAAS can provide precision GPS appoaches with
performance comparable to ILS (Cat 1).

Yes, congratulations. I was misinformed (behind the times, actually), and
for once you actually have the right answer.

Thank you for the correction.

Peter Duniho wrote:

"Jessica Taylor" wrote in message
...
WAAS is insufficient for a precision GPS approach.

Nonsense. A fully deployed WAAS can provide precision GPS appoaches with
performance comparable to ILS (Cat 1).

Yes, congratulations. I was misinformed (behind the times, actually), and
for once you actually have the right answer.

Thank you for the correction.

Always a pleasure to help get you up to the times, Peter.

Jessica Taylor wrote:

WAAS is insufficient for a precision GPS approach.

Nonsense. A fully deployed WAAS can provide precision GPS appoaches with
performance comparable to ILS (Cat 1).

GPS precision approaches use "LAAS",

Not necessarily. In addition to WAAS, JPALS may be used in the future.

which is basically the same as WAAS except that the differential
station is much closer to the airport

LAAS transmits signals on the UHF band. WAAS does not. LAAS can eventually
provide more accuracy.

OK, who is this Jessica dudette? Seems to be uncannily knowledgeable.

It may depend on the meaning of "precision." If you assume any
approach with vertical guidance then WAAS does. If you mean CAT I or
better that depends on where WAAS is/gets to performance wise. It was
supposed to provide CAT I but has had problems.

I have not kept up to date on LAAS but last I heard it may or may not
be developed.

Ron Lee

In article ,
(Ron Lee) wrote:

It may depend on the meaning of "precision."

Historically, "precision" wrt precision approach means only that it provides
vertical guidance.

--
Bob Noel
Looking for a sig the
lawyers will hate

"Ron Lee" wrote in message
...
It may depend on the meaning of "precision." If you assume any
approach with vertical guidance then WAAS does. If you mean CAT I or
better that depends on where WAAS is/gets to performance wise. It was
supposed to provide CAT I but has had problems.

As Bob says, the word "precision" simply implies vertical guidance.

As for whether one can actually get Cat I minima with WAAS, I'm taking the
FAA's word for it. I didn't bother to look for any GPS LPV approaches
specifically to see that they actually exist. I just know that the FAA web
site says (via press release) that as of Oct 2004, they were starting to
roll out Cat I-equivalent GPS approaches.