Questions on high altitude pressures

[es330td]

At low altitudes the rule of thumb is that a one thousand foot
increase in altitude results in a one inch of mercury decrease in
pressure; at least that is what happens when I turn the little knob on
my altimeter. Since commercial planes flight well into the FL300+
range, clearly that rule cannot hold at altitude as a plane taking off
at 29.92 inches would find itself in a vacuum at 29,900 feet above sea
level. Can someone with experience of high altitude flight expand on
my understanding of pressure variation?

Also, since the altimeter in the C182 I fly appears to incorporate
that rule of thumb, is it accurate at say, FL120, or is another kind
of altimeter needed for planes flying up there?

TIA

[[email protected]]

es330td > wrote:
> At low altitudes the rule of thumb is that a one thousand foot
> increase in altitude results in a one inch of mercury decrease in
> pressure; at least that is what happens when I turn the little knob on
> my altimeter. Since commercial planes flight well into the FL300+
> range, clearly that rule cannot hold at altitude as a plane taking off
> at 29.92 inches would find itself in a vacuum at 29,900 feet above sea
> level. Can someone with experience of high altitude flight expand on
> my understanding of pressure variation?
>
> Also, since the altimeter in the C182 I fly appears to incorporate
> that rule of thumb, is it accurate at say, FL120, or is another kind
> of altimeter needed for planes flying up there?
>
> TIA

The relation between altitude and pressure is actually logrithmic, but
up to about 10,000 feet or so the rule of thumb is pretty close.

For a chart of altitude versus pressure up to 100,000 feet, see:

http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

Everybodies altimeter is the same and the nonlinear nature of the
atmosphere is one of the reasons everyone sets the altimeter to
29.92 in the flight levels.


--
Jim Pennino

Remove .spam.sux to reply.

[terry]

On Nov 24, 5:40*pm, es330td > wrote:
> At low altitudes the rule of thumb is that a one thousand foot
> increase in altitude results in a one inch of mercury decrease in
> pressure; at least that is what happens when I turn the little knob on
> my altimeter. *Since commercial planes flight well into the FL300+
> range, clearly that rule cannot hold at altitude as a plane taking off
> at 29.92 inches would find itself in a vacuum at 29,900 feet above sea
> level. *Can someone with experience of high altitude flight expand on
> my understanding of pressure variation?
>
> Also, since the altimeter in the C182 I fly appears to incorporate
> that rule of thumb, is it accurate at say, FL120, or is another kind
> of altimeter needed for planes flying up there?

Heres an equation which gives the official ISA atmsopheric pressure
(mbar) as a function of altitude in km. you can put this equation in
excel and plot it yourself. When you plot it you will see the pressure
fall off pretty much linearly until about 15000 ft then it curves
upwards.

Press (mbar) = (101325*(1-6.5*altitude/288.15)^(9.80665*28.9644/
(8.31432*6.5)))/100

at 12000 ft the rule of thumb of 30 mb per 1000 ft gives you 653 mb
while the official ISA value from the above equation is 644 mb which
is pretty damn close. But then when you get to say 30000 ft there is
a big error in using the rule of thumb ( 113 mb vs 301 ISA)

Heres the reference if you want to look it up.
http://wahiduddin.net/calc/density_altitude.htm

Terry
PPL Downunder
sorry about the units. where metricated downunder.

[es330td]

This brings up an interesting wrinkle then as GPS altitude info is not
dependent on external pressure so pilots must be careful to ignore
that info if available. As stated before, in Class A everyone sets
their altimeter to 29.92 so that as long as everyone is wrong together
everything is okay. Adding GPS info into the mix splits the groups
into two; one that is wrong together at 29.92 and another that is
right at actual altitude.

Thanks for the answers.

[Robert Moore]

es330td > wrote
> Adding GPS info into the mix splits the groups
> into two; one that is wrong together at 29.92 and
> another that is right at actual altitude.

Just an extra point....above the transition altitude/level,
we fly a Flight Level, not an Altitude.

Bob Moore

[a[_3_]]

Not nearly as helpful as some of the other posts, but to give you a
sense of how things change, the pressure at 18,000 feet is about half
of that on the surface (30 inches of Hg on the surface, 15 at 18,000
feet). It's halved again at twice that altitude (7.5 inches at
36,000) and halved again at twice that altitude (3.7 inches at 72,000
feet).




On Nov 24, 1:40*am, es330td > wrote:
> At low altitudes the rule of thumb is that a one thousand foot
> increase in altitude results in a one inch of mercury decrease in
> pressure; at least that is what happens when I turn the little knob on
> my altimeter. *Since commercial planes flight well into the FL300+
> range, clearly that rule cannot hold at altitude as a plane taking off
> at 29.92 inches would find itself in a vacuum at 29,900 feet above sea
> level. *Can someone with experience of high altitude flight expand on
> my understanding of pressure variation?
>
> Also, since the altimeter in the C182 I fly appears to incorporate
> that rule of thumb, is it accurate at say, FL120, or is another kind
> of altimeter needed for planes flying up there?
>
> TIA

[Darkwing]

"Wolfgang Schwanke" > wrote in message
...
> es330td > wrote in
> :
>
>> This brings up an interesting wrinkle then as GPS altitude info is not
>> dependent on external pressure so pilots must be careful to ignore
>> that info if available. As stated before, in Class A everyone sets
>> their altimeter to 29.92 so that as long as everyone is wrong together
>> everything is okay. Adding GPS info into the mix splits the groups
>> into two; one that is wrong together at 29.92 and another that is
>> right at actual altitude.
>
> Actually there are two reasons not to use GPS as altimeter.
>
> The first is the one you stated: When flying in an airspace where
> Flight Levels are used, everyone is suppoed to use an agreed-upon
> altimeter setting. The result is that everyone flies along planes of
> equal air pressure, the purpose being to ensure separation. The
> aircraft's real distance from the ground or sea level is unknown,
> irrelevant and can actually fluctuate with weather. But since all
> aircraft measure the same "error" that is OK. If some of the airctrafts
> would use a different measurement method (e.g. GPS or QNH altimeter
> setting) that would defeat the whole system.
>
> In theory you could use GPS altitudes when flying MSL/QNH setting,
> because both systems measure absolute altitued, so you would expect
> them to be the same. If GPS could be relied upon that is. Unfortunately
> it cannot, GPS altitued measurements are unrealiable and can drift
> wildly (as opposed to GPS 2D positioning which is quite accurate).
> Traditional altimeters are much better.
>
> --
> I'd like to jump right on the floor


If GPS altitude is unreliable how do you shot a GPS approach or is this why
WAAS was implemented?

[Mike]

"Darkwing" <theducksmail"AT"yahoo.com> wrote in message
...
>
> "Wolfgang Schwanke" > wrote in message
> ...
>> es330td > wrote in
>> :
>>
>>> This brings up an interesting wrinkle then as GPS altitude info is not
>>> dependent on external pressure so pilots must be careful to ignore
>>> that info if available. As stated before, in Class A everyone sets
>>> their altimeter to 29.92 so that as long as everyone is wrong together
>>> everything is okay. Adding GPS info into the mix splits the groups
>>> into two; one that is wrong together at 29.92 and another that is
>>> right at actual altitude.
>>
>> Actually there are two reasons not to use GPS as altimeter.
>>
>> The first is the one you stated: When flying in an airspace where
>> Flight Levels are used, everyone is suppoed to use an agreed-upon
>> altimeter setting. The result is that everyone flies along planes of
>> equal air pressure, the purpose being to ensure separation. The
>> aircraft's real distance from the ground or sea level is unknown,
>> irrelevant and can actually fluctuate with weather. But since all
>> aircraft measure the same "error" that is OK. If some of the airctrafts
>> would use a different measurement method (e.g. GPS or QNH altimeter
>> setting) that would defeat the whole system.
>>
>> In theory you could use GPS altitudes when flying MSL/QNH setting,
>> because both systems measure absolute altitued, so you would expect
>> them to be the same. If GPS could be relied upon that is. Unfortunately
>> it cannot, GPS altitued measurements are unrealiable and can drift
>> wildly (as opposed to GPS 2D positioning which is quite accurate).
>> Traditional altimeters are much better.
>>
>> --
>> I'd like to jump right on the floor
>
>
> If GPS altitude is unreliable how do you shot a GPS approach or is this
> why WAAS was implemented?

Exactly. WAAS corrects GPS errors and makes the receiver accurate enough to
perform the equivalent of a Cat I ILS approach. If LAAS is ever
implemented, it will allow the GPS equivalent of Cat III approaches.

[[email protected]]

Darkwing <theducksmail"AT"yahoo.com> wrote:
>
> "Wolfgang Schwanke" > wrote in message
> ...
>> es330td > wrote in
>> :
>>
>>> This brings up an interesting wrinkle then as GPS altitude info is not
>>> dependent on external pressure so pilots must be careful to ignore
>>> that info if available. As stated before, in Class A everyone sets
>>> their altimeter to 29.92 so that as long as everyone is wrong together
>>> everything is okay. Adding GPS info into the mix splits the groups
>>> into two; one that is wrong together at 29.92 and another that is
>>> right at actual altitude.
>>
>> Actually there are two reasons not to use GPS as altimeter.
>>
>> The first is the one you stated: When flying in an airspace where
>> Flight Levels are used, everyone is suppoed to use an agreed-upon
>> altimeter setting. The result is that everyone flies along planes of
>> equal air pressure, the purpose being to ensure separation. The
>> aircraft's real distance from the ground or sea level is unknown,
>> irrelevant and can actually fluctuate with weather. But since all
>> aircraft measure the same "error" that is OK. If some of the airctrafts
>> would use a different measurement method (e.g. GPS or QNH altimeter
>> setting) that would defeat the whole system.
>>
>> In theory you could use GPS altitudes when flying MSL/QNH setting,
>> because both systems measure absolute altitued, so you would expect
>> them to be the same. If GPS could be relied upon that is. Unfortunately
>> it cannot, GPS altitued measurements are unrealiable and can drift
>> wildly (as opposed to GPS 2D positioning which is quite accurate).
>> Traditional altimeters are much better.
>>
>> --
>> I'd like to jump right on the floor
>
>
> If GPS altitude is unreliable how do you shot a GPS approach or is this why
> WAAS was implemented?

GPS specified altitude accuracy with Selective Availility (SA) turned
off is +/- 150 m.

WASS specified altitude accuracy is +/- 7.6 m.

Typical actuals are usually +/- 4.7 m and 1.3 m respectively, but not
guaranteed at any particular place and time.

The goal of LAAS is to provide a guaranteed accuracy of less than 1 m.


--
Jim Pennino

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[Allen[_1_]]

"Darkwing" <theducksmail"AT"yahoo.com> wrote in message
...
>
> "Wolfgang Schwanke" > wrote in message
> ...
>> es330td > wrote in

>>
>> In theory you could use GPS altitudes when flying MSL/QNH setting,
>> because both systems measure absolute altitued, so you would expect
>> them to be the same. If GPS could be relied upon that is. Unfortunately
>> it cannot, GPS altitued measurements are unrealiable and can drift
>> wildly (as opposed to GPS 2D positioning which is quite accurate).
>> Traditional altimeters are much better.
>>
>> --
>> I'd like to jump right on the floor
>
>
> If GPS altitude is unreliable how do you shot a GPS approach or is this
> why WAAS was implemented?

Standard GPS approaches a flown with the altitudes from the altimeter. WAAS
approaches rely on GPS position correction from a local transmitter.


--

*H. Allen Smith*
WACO - We are all here, because we are not all there.

[Mxsmanic]

es330td writes:

> This brings up an interesting wrinkle then as GPS altitude info is not
> dependent on external pressure so pilots must be careful to ignore
> that info if available. As stated before, in Class A everyone sets
> their altimeter to 29.92 so that as long as everyone is wrong together
> everything is okay. Adding GPS info into the mix splits the groups
> into two; one that is wrong together at 29.92 and another that is
> right at actual altitude.

GPS is too inaccurate for most purposes in vertical positioning, anyway. It
is not designed to determine altitude with a high degree of accuracy, and can
easily be hundreds of feet off.

[Bob Noel[_4_]]

In article >,
Wolfgang Schwanke > wrote:

> In theory you could use GPS altitudes when flying MSL/QNH setting,
> because both systems measure absolute altitued, so you would expect
> them to be the same. If GPS could be relied upon that is. Unfortunately
> it cannot, GPS altitued measurements are unrealiable and can drift
> wildly (as opposed to GPS 2D positioning which is quite accurate).
> Traditional altimeters are much better.

as a rule of thumb, regular SPS GPS altitude error is roughly
50% greater than the horizontal error.

The advantage of traditional altimeters is realized when everyone
is using them (and the same setting).

Note that above FL290 traditional altimeters errors increase to
the point where separations were increased to 2000' vertical
separations (except for RVSM airspace)

[es330td]

On Nov 24, 8:38*am, Robert Moore > wrote:
> es330td > wrote
>
> Just an extra point....above the transition altitude/level,
> we fly a Flight Level, not an Altitude.
>

Thanks for the reminder. I hope someday to have to care about that. :-)

[Robert Moore]

es330td > wrote

> On Nov 24, 8:38*am, Robert Moore > wrote:
>> es330td > wrote
>>
>> Just an extra point....above the transition altitude/level,
>> we fly a Flight Level, not an Altitude.
>>
>
> Thanks for the reminder. I hope someday to have to care about that. :-)

Just remember.... on the way up, it's Transition Altitude, on the way
down, it's Transition Level. :-)

Bob Moore
ATP CFI
PanAm(retired)

[Dave Doe]

In article >, says...
> Bob Noel > wrote in
> :
>
> > as a rule of thumb, regular SPS GPS altitude error is roughly
> > 50% greater than the horizontal error.
>
> That would be minimal. But IME, while most of the time it's fairly
> accurate, it can sometimes go wild. For example I was cross-countrying
> at 3,500ish ft, when suddenly the GPS went through 3,000 2,500 ...
> 4,500 4,000 and then settled down at 3,500 once again as if nothing had
> happend. It all lasted just a couple of seconds. It had not lost
> coverage, that would be indicated by an error screen and the map
> animation stopping which it did not; model GPS Pilot III. I understand
> this is normal behaviour. If so, GPS altitude measurements are
> completely unreliable.

No way. The screen you shoulda been looking at is the satellite screen
(I bet if you'd been watching that, you'd have noticed some had dropped
out or gone weak).

I've taken my GPS on a number of commercial flights and it's interesting
to watch the differences between FL and GPS indicated alt (as one moves
through high and low pressures).

--
Duncan

[Bob Noel[_4_]]

In article >,
Wolfgang Schwanke > wrote:

> Bob Noel > wrote in
> :
>
> > as a rule of thumb, regular SPS GPS altitude error is roughly
> > 50% greater than the horizontal error.
>
> That would be minimal. But IME, while most of the time it's fairly
> accurate, it can sometimes go wild. For example I was cross-countrying
> at 3,500ish ft, when suddenly the GPS went through 3,000 2,500 ...
> 4,500 4,000 and then settled down at 3,500 once again as if nothing had
> happend. It all lasted just a couple of seconds. It had not lost
> coverage, that would be indicated by an error screen and the map
> animation stopping which it did not; model GPS Pilot III. I understand
> this is normal behaviour. If so, GPS altitude measurements are
> completely unreliable.

A properly operating GPS receiver, with 4 SVs in view in an
appropriate geometry, should not report such extreme altitude
variations.

What is unknown: exactly how the GPS Pilot III selects SVs,
whether or not it will require 4 in view or let altitude "drift"
in order to maintain a 2D solution by using just 3 SVs, whether
or not it will report outages/drops within a few seconds, whether
or not it performs reasonableness checks on solutions.

I assume the GPS Pilot III doesn't have RAIM or FDE

[Mxsmanic]

Bob Noel writes:

> as a rule of thumb, regular SPS GPS altitude error is roughly
> 50% greater than the horizontal error.

GPS altitude error is enormous, sometimes two orders of magnitude greater than
lateral error. It's completely unreliable.

[[email protected]]

Mxsmanic > wrote:
> Bob Noel writes:
>
>> as a rule of thumb, regular SPS GPS altitude error is roughly
>> 50% greater than the horizontal error.
>
> GPS altitude error is enormous, sometimes two orders of magnitude greater than
> lateral error. It's completely unreliable.

Wrong yet again.

Two orders of magnitude means 100 times.

The GPS specification with SA on is 100 m lateral, 150 m vertical, which
is 1.5 times.

GPS measured accuracy with SA off is 2.5 m lateral, 4.7 m vertical, which
is 1.9 times.

WASS specification is 7.6 m lateral, 7.6 m vertical, which is 1 times.

WASS measured accuracy is 0.9 m lateral, 1.3 m vertical, which is
1.4 times.

In all cases, altitude error is less than 2 times lateral error.

It looks as though we can add GPS and simple arithmetic to the list of
things which you pontificate about yet know nothing about.


--
Jim Pennino

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[Mxsmanic]

writes:

> Two orders of magnitude means 100 times.

Yes, I know.

> The GPS specification with SA on is 100 m lateral, 150 m vertical, which
> is 1.5 times.

SA has been off for years.

> GPS measured accuracy with SA off is 2.5 m lateral, 4.7 m vertical, which
> is 1.9 times.

The vertical accuracy is far worse than 4.7 metres.

> It looks as though we can add GPS and simple arithmetic to the list of
> things which you pontificate about yet know nothing about.

Be sure to fly IFR sometime in IMC with GPS as your altimeter, and you'll see
what I mean.

[[email protected]]

Mxsmanic > wrote:
> writes:
>
>> Two orders of magnitude means 100 times.
>
> Yes, I know.
>
>> The GPS specification with SA on is 100 m lateral, 150 m vertical, which
>> is 1.5 times.
>
> SA has been off for years.

Yes, that at least is correct.

The point is that even with SA, GPS accuracy is pretty good and has nowhere
near 2 orders of magnitude altitude error compared to lateral as you stated.

>> GPS measured accuracy with SA off is 2.5 m lateral, 4.7 m vertical, which
>> is 1.9 times.
>
> The vertical accuracy is far worse than 4.7 metres.

Absolutely wrong.

See the the data:

http://users.erols.com/dlwilson/gpswaas.htm

GPS with SA off, vertical error:

No WAAS

50% 3.0 m
Mean 3.6 m
RMS 4.5 m

With WAAS:

50% 2.2 m
Mean 2.6 m
RMS 3.2 m

A quick Google (source of all your knowledge) finds numerous sites
with similar data.

You are wrong, wrong, wrong once again.

>> It looks as though we can add GPS and simple arithmetic to the list of
>> things which you pontificate about yet know nothing about.
>
> Be sure to fly IFR sometime in IMC with GPS as your altimeter, and you'll see
> what I mean.

If you knew anything about real flying, you would know that you NEVER
use GPS as your altimeter under ANY circumstances for reasons entirely
unlrelated to GPS accuracy.

But how would you know as you have never been in a real airplane with
a real altimeter and a real GPS?


--
Jim Pennino

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[Mxsmanic]

writes:

> The point is that even with SA, GPS accuracy is pretty good and has nowhere
> near 2 orders of magnitude altitude error compared to lateral as you stated.

You call a 500-foot error in altitude good?

> Absolutely wrong.

All I have to do is look at my GPS and watch it wander up and down by tens of
metres at a time. GPS is not designed for vertical accuracy.

> See the the data:
>
> http://users.erols.com/dlwilson/gpswaas.htm

"The" data? It's just one person making experiments. I can do that, too; and
I get huge errors in altitude, so much so that I've never used GPS for
altitude measurements.

> If you knew anything about real flying, you would know that you NEVER
> use GPS as your altimeter under ANY circumstances for reasons entirely
> unlrelated to GPS accuracy.

What are those reasons related to, if not accuracy?

If it's as accurate as you seem to believe, it should be fine for IFR. Go
ahead and use it for that, and make me a liar. Are you prepared to bet your
life on it?

> But how would you know as you have never been in a real airplane with
> a real altimeter and a real GPS?

I've been using GPS for many years. It's almost useless for measuring
altitude.

[[email protected]]

Mxsmanic > wrote:
> writes:
>
>> The point is that even with SA, GPS accuracy is pretty good and has nowhere
>> near 2 orders of magnitude altitude error compared to lateral as you stated.
>
> You call a 500-foot error in altitude good?

That's 492 feet with SA on, which as you've already acknowledged has been
off for a long time.

>> Absolutely wrong.
>
> All I have to do is look at my GPS and watch it wander up and down by tens of
> metres at a time. GPS is not designed for vertical accuracy.

YOUR GPS receiver is not designed for vertical accuracy because you are
too poor to be able to afford a decent one.

>> See the the data:
>>
>> http://users.erols.com/dlwilson/gpswaas.htm
>
> "The" data? It's just one person making experiments.

I can point you to dozens of sites with similar data and the GPS
specs as well, but you could just do it yourself and admit for once
that you are wrong.

>> If you knew anything about real flying, you would know that you NEVER
>> use GPS as your altimeter under ANY circumstances for reasons entirely
>> unlrelated to GPS accuracy.
>
> What are those reasons related to, if not accuracy?

Regulations, the nature of real air, the way real airplanes fly and
common sense.

Beg for some money, give the money to a CFI, and it will be explained
in detail to you.

> If it's as accurate as you seem to believe, it should be fine for IFR.

Regulations, the nature of real air, the way real airplanes fly and
common sense.

>> But how would you know as you have never been in a real airplane with
>> a real altimeter and a real GPS?
>
> I've been using GPS for many years. It's almost useless for measuring
> altitude.

YOUR GPS receiver is not designed for vertical accuracy because you are
too poor to be able to afford a decent one.

MY non-WAAS, aviation GPS receiver measures altitude that is within about
+/- 15 feet, or about +/- 4m, which is what everyone with a real GPS
gets.

So, to summarize:

You know nothing about GPS specifications.

You know nothing about aviation use of GPS.

Because you are such an arrogant, opinionated ass, you can't get a job
that would enable you to afford a decent GPS receiver.

That about sum it up?

I doubt the time accuracy on your piece of crap GPS is anywhere near
the nanosecond capabilities of a decent receiver either.


--
Jim Pennino

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[Viperdoc[_6_]]

Anthony, what kind of GPS are you using- is it a Garmin 530/430 with WAAS?
How many satellites do you track at a time- or are you referring to playing
MSFS again and confusing it with reality?

[[email protected]]

Viperdoc > wrote:
> Anthony, what kind of GPS are you using- is it a Garmin 530/430 with WAAS?
> How many satellites do you track at a time- or are you referring to playing
> MSFS again and confusing it with reality?

I would guess an old Tom-tom someone threw away.


--
Jim Pennino

Remove .spam.sux to reply.

[Mxsmanic]

writes:

> YOUR GPS receiver is not designed for vertical accuracy because you are
> too poor to be able to afford a decent one.

The GPS system is not designed for vertical accuracy. It was designed as an
aid to lateral navigation. The geometry of the system does not favor vertical
accuracy.

> I can point you to dozens of sites with similar data and the GPS
> specs as well, but you could just do it yourself and admit for once
> that you are wrong.

I can point you to dozens of sites that "prove" that Denver's airport overlies
a huge alien base underground, but that doesn't make it so.

> Regulations, the nature of real air, the way real airplanes fly and
> common sense.

If GPS were accurate, why would any of these other factors make a difference?

> Beg for some money, give the money to a CFI, and it will be explained
> in detail to you.

I know a lot more about how GPS works than the typical CFI.

> Regulations, the nature of real air, the way real airplanes fly and
> common sense.

See above. Why wouldn't regulations allow something that is as accurate as
you say?

> YOUR GPS receiver is not designed for vertical accuracy because you are
> too poor to be able to afford a decent one.

They cannot be designed for vertical accuracy. The system itself is not
designed for that.

> MY non-WAAS, aviation GPS receiver measures altitude that is within about
> +/- 15 feet, or about +/- 4m, which is what everyone with a real GPS
> gets.

How do you know?

> I doubt the time accuracy on your piece of crap GPS is anywhere near
> the nanosecond capabilities of a decent receiver either.

Actually, they all need nanosecond accuracy. But if you know how GPS works,
you already know that, right?

[Mxsmanic]

Viperdoc writes:

> Anthony, what kind of GPS are you using- is it a Garmin 530/430 with WAAS?

In real life? I have a handheld Garmin. In simulation? A 530 and a 430,
without WAAS (but they are always completely accurate in simulation, anyway).

> How many satellites do you track at a time- or are you referring to playing
> MSFS again and confusing it with reality?

In real life, up to twelve satellites simultaneously.

[Mxsmanic]

Clark writes:

> Of course mxy is ignorant of the current GPS performance and too stupid to
> understand that the technology has improved.

The design has not changed, and unless the planet becomes transparent to GPS
signals, accuracy cannot improve much.

[[email protected]]

Mxsmanic > wrote:
> writes:
>
>> YOUR GPS receiver is not designed for vertical accuracy because you are
>> too poor to be able to afford a decent one.
>
> The GPS system is not designed for vertical accuracy. It was designed as an
> aid to lateral navigation. The geometry of the system does not favor vertical
> accuracy.

You are making yourself look the fool more than ever.

Both the specifications and typical results for vertical versus lateral
error for SA on, SA off, and WAAS are all less than 2:1, not the 100:1
you claim.

>> I can point you to dozens of sites with similar data and the GPS
>> specs as well, but you could just do it yourself and admit for once
>> that you are wrong.
>
> I can point you to dozens of sites that "prove" that Denver's airport overlies
> a huge alien base underground, but that doesn't make it so.

Sure, you can find kook sites, but that is an irrelevant red herring.

GPS error has been studied and results published on the web by lots
of univerities, major corporations, and government agencies, including
the NIST and the FAA.

The full specifications for GPS are publically available.

All say you are wrong, wrong, wrong.

>> Regulations, the nature of real air, the way real airplanes fly and
>> common sense.
>
> If GPS were accurate, why would any of these other factors make a difference?

Start with the fact that not all real airplanes have GPS and not all real
airplanes that have GPS have WAAS capable GPS and no real airplane has a
"pause" key and see if you can figure it out.

> I know a lot more about how GPS works than the typical CFI.

From your statements so far, i.e. vertical error is two orders of magnitude
greater than lateral error, it appears you know nothing about GPS other
than how to spell it.

> They cannot be designed for vertical accuracy. The system itself is not
> designed for that.

Wrong, wrong wrong.

You might try reading the actual GPS system specifications before you
make such inane statements.

>> MY non-WAAS, aviation GPS receiver measures altitude that is within about
>> +/- 15 feet, or about +/- 4m, which is what everyone with a real GPS
>> gets.
>
> How do you know?

By looking at the displayed GPS altitude while on the ground and comparing
that to the published field elevation.

By looking at the displayed GPS altitude and comparing to the surveyed
altitude of my location, e.g. my house.

That should be obvious to anyone with more than two functioning brain
cells.

>> I doubt the time accuracy on your piece of crap GPS is anywhere near
>> the nanosecond capabilities of a decent receiver either.
>
> Actually, they all need nanosecond accuracy.

Wrong again.

Time accuracy is a measure of the error in the GPS time of day output,
just like for position, which includes a 1 pps signal.

Most consumer grade GPS receivers do not contain the circuitry needed
for nanosecond accurate time of day output.

And before you make yourself even more a fool on this point too, you might
want to go see what the National Institute of Standards and Technology
has to say on the subject.


--
Jim Pennino

Remove .spam.sux to reply.

[[email protected]]

Mxsmanic > wrote:
> Clark writes:
>
>> Of course mxy is ignorant of the current GPS performance and too stupid to
>> understand that the technology has improved.
>
> The design has not changed, and unless the planet becomes transparent to GPS
> signals, accuracy cannot improve much.

Wrong yet again.

SA turned off, differential GPS, WAAS, and LAAS.

--
Jim Pennino

Remove .spam.sux to reply.

[John E. Carty]

"Mxsmanic" > wrote in message
...
> writes:
>
>> YOUR GPS receiver is not designed for vertical accuracy because you are
>> too poor to be able to afford a decent one.
>
> The GPS system is not designed for vertical accuracy. It was designed as
> an
> aid to lateral navigation. The geometry of the system does not favor
> vertical
> accuracy.
>
>> I can point you to dozens of sites with similar data and the GPS
>> specs as well, but you could just do it yourself and admit for once
>> that you are wrong.
>
> I can point you to dozens of sites that "prove" that Denver's airport
> overlies
> a huge alien base underground, but that doesn't make it so.
>
>> Regulations, the nature of real air, the way real airplanes fly and
>> common sense.
>
> If GPS were accurate, why would any of these other factors make a
> difference?
>
>> Beg for some money, give the money to a CFI, and it will be explained
>> in detail to you.
>
> I know a lot more about how GPS works than the typical CFI.
>
>> Regulations, the nature of real air, the way real airplanes fly and
>> common sense.
>
> See above. Why wouldn't regulations allow something that is as accurate
> as
> you say?
>
>> YOUR GPS receiver is not designed for vertical accuracy because you are
>> too poor to be able to afford a decent one.
>
> They cannot be designed for vertical accuracy. The system itself is not
> designed for that.
>
>> MY non-WAAS, aviation GPS receiver measures altitude that is within about
>> +/- 15 feet, or about +/- 4m, which is what everyone with a real GPS
>> gets.
>
> How do you know?
>
>> I doubt the time accuracy on your piece of crap GPS is anywhere near
>> the nanosecond capabilities of a decent receiver either.
>
> Actually, they all need nanosecond accuracy. But if you know how GPS
> works,
> you already know that, right?

I usually refrain from this kind of post. However, you absolutely must be
one of the following:

A: A computer simulator "pilot"
B: An Idiot
C: Both A and B

:-)

[Viperdoc[_6_]]

Anthony will never admit that he's wrong, nor will he ever accept a point of
view offered by others.

This is why he is a social outcast and can not find or hold a job.

[Blanche]

And please remember that GPS altitude is based on an "imaginary"
or mathematical model of the earth's surface. Right now I have mine
set to WGS 84. But there are numerous other geodetic datums, such as
WGS 72, Zanderij, and so on.

[Blanche]

Mxsmanic > wrote:

>I can point you to dozens of sites that "prove" that Denver's airport overlies
>a huge alien base underground, but that doesn't make it so.

Kewl! Tell me where, and I'll drive over and check it out!

[Mxsmanic]

writes:

> SA turned off, differential GPS, WAAS, and LAAS.

Differential GPS, WAAS, and LAAS are not part of the GPS system.

[[email protected]]

Mxsmanic > wrote:
> writes:
>
>> SA turned off, differential GPS, WAAS, and LAAS.
>
> Differential GPS, WAAS, and LAAS are not part of the GPS system.

WAAS most certainly is part of the GPS system, LAAS is in development, and
differential is a matter of interpretation.

You won't see any improvement from WAAS because France isn't in the
current service area.

If you don't like those examples of GPS system improvements,
here are some of the following since 1978:

Six distinct satellite families, each progressively better, 1978-2009.

SA turned off circa 2000.

L2C added to Block IIR-M and newer satellites circa 2005.

Total of 31 satellites and the constellation changed to a nonuniform
arrangement circa 2008.

The CNAV message added to upgrade the original NAV message.

The L5 and the L1C messages in work.

Further improvements, called GPS III, are planned to be all operational
by 2013, with incentives offered to the contractors if they can
complete it by 2011.

In summary, you don't know **** from shinola about how GPS works or the
history of GPS.


--
Jim Pennino

Remove .spam.sux to reply.

[[email protected]]

Blanche > wrote:
> And please remember that GPS altitude is based on an "imaginary"
> or mathematical model of the earth's surface. Right now I have mine
> set to WGS 84. But there are numerous other geodetic datums, such as
> WGS 72, Zanderij, and so on.

To get real altitude data in general, the receiver must have the smarts
and internal data to do the corrections.

Consumer hiking receivers generally don't have such capabilities.

--
Jim Pennino

Remove .spam.sux to reply.

[Mxsmanic]

writes:

> WAAS most certainly is part of the GPS system, LAAS is in development, and
> differential is a matter of interpretation.

None of them is. They are separate systems that depend on GPS; they are not
part of GPS. Anyone can construct a GPS augmentation system, but that doesn't
make it part of GPS.

> You won't see any improvement from WAAS because France isn't in the
> current service area.

That does not change the fact that WAAS is not part of GPS.

[john smith]

In article >,
wrote:

> The relation between altitude and pressure is actually logrithmic, but
> up to about 10,000 feet or so the rule of thumb is pretty close.
>
> For a chart of altitude versus pressure up to 100,000 feet, see:
>
> http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html
>
> Everybodies altimeter is the same and the nonlinear nature of the
> atmosphere is one of the reasons everyone sets the altimeter to
> 29.92 in the flight levels.

Now make it even more interesting and convert the two main component of
the air we breath to their partial pressures.

[[email protected]]

Mxsmanic > wrote:
> writes:
>
>> WAAS most certainly is part of the GPS system, LAAS is in development, and
>> differential is a matter of interpretation.
>
> None of them is. They are separate systems that depend on GPS; they are not
> part of GPS. Anyone can construct a GPS augmentation system, but that doesn't
> make it part of GPS.
>
>> You won't see any improvement from WAAS because France isn't in the
>> current service area.
>
> That does not change the fact that WAAS is not part of GPS.

Drooling nonsense.

You obviously haven't a clue how WAAS works.

--
Jim Pennino

Remove .spam.sux to reply.

[[email protected]]

wrote:
> Mxsmanic > wrote:
>> writes:
>>
>>> WAAS most certainly is part of the GPS system, LAAS is in development, and
>>> differential is a matter of interpretation.
>>
>> None of them is. They are separate systems that depend on GPS; they are not
>> part of GPS. Anyone can construct a GPS augmentation system, but that doesn't
>> make it part of GPS.
>>
>>> You won't see any improvement from WAAS because France isn't in the
>>> current service area.
>>
>> That does not change the fact that WAAS is not part of GPS.
>
> Drooling nonsense.
>
> You obviously haven't a clue how WAAS works.
>

I forgot to mention I noticed you snipped the list of changes to the
GPS system you said don't exist.


--
Jim Pennino

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[Dave Doe]

In article >,
says...
> writes:
>
> > WAAS most certainly is part of the GPS system, LAAS is in development, and
> > differential is a matter of interpretation.
>
> None of them is. They are separate systems that depend on GPS; they are not
> part of GPS. Anyone can construct a GPS augmentation system, but that doesn't
> make it part of GPS.
>
> > You won't see any improvement from WAAS because France isn't in the
> > current service area.
>
> That does not change the fact that WAAS is not part of GPS.

There is no need to so aptly demonstrate your stupidity.

What is WAAS or RAIM etc etc - any aviation GPS technology - without GPS
itself?

These technologies are little more than GPS enhancements so that
aviators can use them to provided required and determined accuracy.

GPS is otherwise useless for aviation - handy for a VFR pilot - but it
must not be relied on for either altitude or positional data - it's an
aid only.

Coupled with (say) WAAS - the GPS becomes a reliable intrument for an
instrument approach.

Pull your head out of your arse.

--
Duncan

[Beauciphus]

"Viperdoc" > wrote in message
...
> Anthony will never admit that he's wrong, nor will he ever accept a point
> of view offered by others.
>
> This is why he is a social outcast and can not find or hold a job.
>

What kind of troll would ever give up?

All he wants is someone to agrue with. He's found that here. Too bad he
wrecked the place in teh process.

[Mxsmanic]

Dave Doe writes:

> What is WAAS or RAIM etc etc - any aviation GPS technology - without GPS
> itself?

WAAS is a navigation technology that relies on GPS. It is not _part_ of GPS.

> These technologies are little more than GPS enhancements so that
> aviators can use them to provided required and determined accuracy.

RAIM isn't even that much, but WAAS is an augmentation technology. The fact
remains that it isn't part of GPS itself.

> GPS is otherwise useless for aviation - handy for a VFR pilot - but it
> must not be relied on for either altitude or positional data - it's an
> aid only.

It's very useful for lateral position in many circumstances, even for
aviation. The altitude data is too unreliable to be useful for aviation.

[Frank Barchi]

"es330td" > wrote in message
...
On Nov 24, 8:38 am, Robert Moore > wrote:
> es330td > wrote
>
> Just an extra point....above the transition altitude/level,
> we fly a Flight Level, not an Altitude.
>

Thanks for the reminder. I hope someday to have to care about that. :-)

Just an extra, extra point.....there is no FL 120

Frank

[Robert Moore]

"Frank Barchi" > wrote

> Just an extra, extra point.....there is no FL 120

Of course there is.....maybe not in your part of the world, but
I seem to recall transition altitudes as low as 6,000' in some of
the places that I have flown. In fact, San Juan's CTA is listed
as starting at FL 25.

Bob Moore
ATP CFI
PanAm (retired)

[[email protected]]

Mxsmanic > wrote:
> Dave Doe writes:
>
>> What is WAAS or RAIM etc etc - any aviation GPS technology - without GPS
>> itself?
>
> WAAS is a navigation technology that relies on GPS. It is not _part_ of GPS.

Wrong again.

WAAS is a subsystem of GPS that transmits localized GPS correction
information for the US via a pair of geosynchronous satellites.

WAAS merely provides one more signal among the many that make up the
GPS system.

> It's very useful for lateral position in many circumstances, even for
> aviation. The altitude data is too unreliable to be useful for aviation.

Wrong again.

With WAAS corrections, the maximum lateral and vertical error is 7.6 m
under all cicumstances, makeing it more than reliable enough to make
vertically-guided landing approaches in IFR.

WAAS LPVs

http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/approaches/index.cfm

--
Jim Pennino

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[Tauno Voipio]

Robert Moore wrote:
> "Frank Barchi" > wrote
>
>> Just an extra, extra point.....there is no FL 120
>
> Of course there is.....maybe not in your part of the world, but
> I seem to recall transition altitudes as low as 6,000' in some of
> the places that I have flown. In fact, San Juan's CTA is listed
> as starting at FL 25.
>
> Bob Moore
> ATP CFI
> PanAm (retired)


In Finland (EF), the transition altitude is 5000 feet.

--

Tauno Voipio (CPL(A), OH-PYM)
tauno voipio (at) iki fi

[george]

On Nov 28, 2:28*am, "Beauciphus" > wrote:

> All he wants is someone to agrue with. He's found that here. Too bad he
> wrecked the place in teh process.

Its like he's the very bad comedy turn on before the strippers.
To get to the good stuff you have to wait through the crap.

[Mxsmanic]

writes:

> WAAS is a subsystem of GPS that transmits localized GPS correction
> information for the US via a pair of geosynchronous satellites.

No, WAAS is an independent system that relies in part on GPS. There are many
such systems (indeed, anyone can set up such a system).

> With WAAS corrections, the maximum lateral and vertical error is 7.6 m
> under all cicumstances, makeing it more than reliable enough to make
> vertically-guided landing approaches in IFR.

With augmentation you can theoretically get any accuracy you want.

[[email protected]]

Mxsmanic > wrote:
> writes:
>
>> WAAS is a subsystem of GPS that transmits localized GPS correction
>> information for the US via a pair of geosynchronous satellites.
>
> No, WAAS is an independent system that relies in part on GPS. There are many
> such systems (indeed, anyone can set up such a system).

Totally and utterly wrong yet again.

http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System
http://www8.garmin.com/aboutGPS/waas.html
http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/waas/howitworks/

Wikipedia says you are wrong.

Garmin says you are wrong.

The FAA says you are wrong.

You are wrong, wrong, wrong.

That's three strikes, you are out.


--
Jim Pennino

Remove .spam.sux to reply.

[Jose Jimenez]

Frank Barchi wrote:

> Just an extra, extra point.....there is no FL 120

You might not be aware of it, but there's actually life (and flying)
outside of the USA.

[Jose Jimenez]

Wolfgang Schwanke wrote:

> In theory you could use GPS altitudes when flying MSL/QNH setting,

No. Even with MSL/QNH setting, as you call it, the barometric altimeter
does *not* show the true geometric altitude. More precisely, it only
shows it in two cases:

1. When sitting on the ground at the reference altitude for the given
altimeter setting (QNH)

2. When the atmosphere happens to be an ICAO standard atmosphere.

[[email protected][_2_]]

Just to throw a little more fuel on this fire - GPS altitude is in
widespread use in the soaring world and has proven to be very useful
for computing height above ground and final glides to destinations.
It can also be used to give vertical motion, although not as
accurately as a pressure instrument.

The biggest difference (other than the previously discussed pressure
altitude vs height above the ellipsoid issue) is that while an
altimeter, when set to the correct pressure (mb or in hg) for QFE or
QNH, is stable in the short term but will become more innacurate over
time due to atmospheric pressure changes (not talking about flight
levels here), GPS is less accurate in the short term (altitude varies
with geometry, etc) but extremely stable over the long term.

I won't waste my time on argueing with Mxsmanic - he is really
clueless - but it sometimes amazes me how many "real" pilots have a
poor grasp on what altimeters really indicate!

Speaking of accuracy, anybody remember what the altitude tolerance of
an altimeter is? In military jets it's +- 75 feet or so - I have no
idea what it is for the non-TSO'd altimeter in my LS6. Which means
that as long as your GPS is tracking 4+ satellites with good geometry
and no SA, it's altitude (QNH) is probably better than what is shown
on your altimeter (but only if you know the difference between MSL and
HAE, which can be over 100' in many places...).

So - use your altimeter (set correctly) for IFR, and use your aviation
GPS to help avoid hitting the hard stuff!

Kirk

[John Smith]

wrote:

> So - use your altimeter (set correctly) for IFR, and use your aviation
> GPS to help avoid hitting the hard stuff!

Actually, I use my eyes for that.

[a[_3_]]

Given the nature of this thread, some of you will enjoy this video,

http://www.grayeagles.org/video.htm

and others will let the lettering on the side of this rebuilt Mustang,
named "Feburary", ruin the entire experience.

The video is worth watching, especially this close to Veteran's Day.

[[email protected][_2_]]

On Nov 28, 9:19*am, John Smith > wrote:
> wrote:
> > So - use your altimeter (set correctly) for IFR, and use your aviation
> > GPS to help avoid hitting the hard stuff!
>
> Actually, I use my eyes for that.

Well, if you can see out the window, who cares about altitude anyway!

Now, at night, no moon, some haze, maybe over water....

Kirk

[John Smith]

wrote:

>>> So - use your altimeter (set correctly) for IFR, and use your aviation
>>> GPS to help avoid hitting the hard stuff!

>> Actually, I use my eyes for that.

> Well, if you can see out the window, who cares about altitude anyway!
>
> Now, at night, no moon, some haze, maybe over water....

Wouldn't that be IFR?

[[email protected][_2_]]

On Nov 29, 3:30*am, John Smith > wrote:
> wrote:
> >>> So - use your altimeter (set correctly) for IFR, and use your aviation
> >>> GPS to help avoid hitting the hard stuff!
> >> Actually, I use my eyes for that.
> > Well, if you can see out the window, who cares about altitude anyway!
>
> > Now, at night, no moon, some haze, maybe over water....
>
> Wouldn't that be IFR?

Or really stupid night VFR...(which I realize is not legal in some
countries).

Of course, there has never been a case of a misset or misread
altimeter resulting in a pilot running a perfectly good airplane into
the ground, has there - especially with those horrible triple-pointer
altimeters! Much harder to do that with a GPS, especially if it has a
terrain database to give AGL height (well, you still have to read the
instruments...). Which is why most modern avionics setups have
exactly that arrangement. And it can be done cheap - $200 PDA with
GPS and some software does the same thing.

Kirk

[Dave Doe]

In article >,
says...
> Dave Doe writes:
>
> > What is WAAS or RAIM etc etc - any aviation GPS technology - without GPS
> > itself?
>
> WAAS is a navigation technology that relies on GPS. It is not _part_ of GPS.

I think you need to stop playing silly word games and grow up.

--
Duncan

[Bertie the Bunyip[_24_]]

Mxsmanic > wrote in
:

> es330td writes:
>
>> This brings up an interesting wrinkle then as GPS altitude info is
>> not dependent on external pressure so pilots must be careful to
>> ignore that info if available. As stated before, in Class A everyone
>> sets their altimeter to 29.92 so that as long as everyone is wrong
>> together everything is okay. Adding GPS info into the mix splits the
>> groups into two; one that is wrong together at 29.92 and another that
>> is right at actual altitude.
>
> GPS is too inaccurate for most purposes in vertical positioning,
> anyway. It is not designed to determine altitude with a high degree
> of accuracy, and can easily be hundreds of feet off.
>


You#re aan idiot.


Bertie