Setting altimeters with no radio

"Travis Marlatte" wrote in
t:

Since
you can't be NORDO in the IFR system, separation is the responsibility
of the pilot's eyes anyway.

Maybe you should say you cannot be INTENTIONALLY NORDO (squawking 7600).

It would be pretty hard to maintian visual separation in the clag should
the radios go belly up.

Allen

You can't begin an IFR flight as NORDO, but you certainly
can complete the flight that way.



"Travis Marlatte" wrote in
message
t...
| "Mxsmanic" wrote in message
| ...
|
| No, it is not. It's especially dangerous for RVSM
flight, but it's so
| inaccurate that it should never be used for anything,
except as a last
| resort (if the altimeters disintegrate, or whatever).
|
|
| It was posed as a possible means to adjust a pressure
altimeter with no
| radio. I'd say that it is better than nothing, in that
case. Since you can't
| be NORDO in the IFR system, separation is the
responsibility of the pilot's
| eyes anyway.
|
| -------------------------------
| Travis
| Lake N3094P
| PWK
|
|

"Mxsmanic" wrote in message
...


No, it is not. It's especially dangerous for RVSM flight, but it's so
inaccurate that it should never be used for anything,

Your complete misunderstanding of the GPS system is showing. I have two
GPS's in the plane, one panel mount and one portable. It is rare that
either one is ever off by more than 100 feet in altitude. Using GPS for
your altitude for VFR flight would be perfectly fine.

Newps writes:

Your complete misunderstanding of the GPS system is showing. I have two
GPS's in the plane, one panel mount and one portable. It is rare that
either one is ever off by more than 100 feet in altitude. Using GPS for
your altitude for VFR flight would be perfectly fine.

I can see the NTSB report now: "Pilot failed to understand limitations
of GPS navigation." But as long as I'm not flying with you, I don't
care. Do what you want.

--
Transpose mxsmanic and gmail to reach me by e-mail.

I recently experimented with flying a GPS approach using the GPS
reported altitude as the "altimeter"... First, I flew the GPS approach
track making notes as to the altimeter reading versus the GPS reported
altitude on two GPS units in the cockpit...

Now, knowing the average local offset between the GPS datum circle and
the local ground altitude as reported by the local barometric pressure
altimeter the official pair of altimeters in the pilots lounge... I
wound up with 79 feet as my averaged offset between the GPS datum plane
and the local altimeter... Notice I am emphasizing the word 'local'
here... Your findings will differ with your area and with what they are
doing down inside that Colorado mountain at any given instant...... A
local WAAS transmitter and a WAAS receiver in my plane would, of
course, narrow that altitude difference... Also note the altitude
delta I found is almost within allowable altimeter error...

Anyway, the second trip around I concentrated on flying the altimeter
and IVSI on the
Garmins instead of the altimeter - jeez, are they twitchy; according to
them I never did establish level flight, they always showed either
climb or descent, albeit usually at a rate of ~10 or 20 fpm... Trying
to fly for real with an altitude instrument this twitchy would be
exhausting.. The descent phase on the various legs of the approach was
interesting but doable...

So, my little experiment shows that one can do a GPS approach - after a
fashion - using the GPS altitude reporting... Knowing in advance what
the local differential between the GPS and the cold hard ground would
be nice...

I intend to next fool around with using the GPS IVSI for flying an ILS
in place of the glide slope... I have done this with the barometric
IVSI and had the radar guys watch me... Two times out of three they
said they could not see any divergence... The one time they did see it
I was definitely off the glide slope as I got sloppy on speed control
and wound up too fast...

Fun stuff to do as opposed to droning around in circles...

denny

Newps wrote:
"Mxsmanic" wrote in message
...


No, it is not. It's especially dangerous for RVSM flight, but it's so
inaccurate that it should never be used for anything,

Your complete misunderstanding of the GPS system is showing. I have two
GPS's in the plane, one panel mount and one portable. It is rare that
either one is ever off by more than 100 feet in altitude. Using GPS for
your altitude for VFR flight would be perfectly fine.

"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

"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.