GPS: it could happen to you
Jim Wolper
A true-life war story with a moral about GPS and
navigation.
I was flying a charter to the Sun Valley Regional Airport
in Hailey, Idaho last night. SUN has an NDB approach which
is not authorized at night, which is too bad because when I
arrived over the beacon it was solid IMC. Oh, you've heard
of Sun Valley, right? The premier ski resort? That's right,
it's surrounded by big high rocks. The A/FD says that
night operations are not recommended for those not familiar
with the airport. You can barely squeeze a VFR pattern
between the runway and the mountains on either side.
Since we had been in and out of rain and snow showers on the
way, we (that is, my passenger and myself) decided to hold
at the beacon for a bit to see if things would clear. We were
below the freezing layer and had plenty of fuel. After about
three turns in the hold I saw enough recognizable lights
ahead that I cancelled and proceeded inbound. The airport
was reporting 10 miles visibility, but, just in case, I
decided to follow the published approach procedure and was
mentally committed to performing the published missed approach
if I didn't like what I saw. The missed approach point is
at the 5.0DME fix from the beacon (yes, there is a DME at
the beacon). But I didn't have DME and I was VFR anyway so
I was going to use the GPS t identify the point where I
would miss.
Now comes the scary part.
Two miles from the beacon the red WARN light on the GPS went on.
It said 1.9NM all the way to touchdown. I believe what
happened is that as we flew into the valley we had loss of signal
due to terrain masking of satellites. Just when I wanted
the GPS the most, it failed.
We made a safe and legal VFR approach nonetheless; we had
the required visibility (even though we couldn't see *&&^$#%$;
there are no obstruction lights on the mountains, so even
with 10 miles visibility we couldn't see them 5 miles away)
and followed the road which we both knew from long experience
leads to the runway.
The point? As Bowditch says, no prudent navigator relies on
any one piece of navigational equipment. Back up that GPS with
something, even if it's only dead reckoning. (And while you're
at it, back up your hard drive, too.)
Dylan Smith
Jim Wolper wrote:
>
> The point? As Bowditch says, no prudent navigator relies on
> any one piece of navigational equipment. Back up that GPS with
> something, even if it's only dead reckoning.
What do you mean 'only' dead reckoning?
A phrase I try to fly by is (OK, I'm just a VFR PPL):
"Dead reckoning is the primary form of navigation.
Everything else is just an _aid_". Of course, under
daytime VFR conditions (and nighttime in populated
areas) pilotage is also pretty primary for VFR navigation.
I read an interesting 'I Learned About Flying From That'
in one of the books by the same name. It was about a
military jet instructor and student who lost their
radios in thick IMC. They had good situational awareness
and managed to dead reckon to the nearest VFR conditions.
--
Email: dy...@vnet.IBM.COM
Dylan Smith 1810 Space Park Drive, Houston, TX 77573
Standard disclaimer applies.
Anti-spam - Change 'r' to raleigh, 'i' to ibm and 'c' to com.
Tim Hogard
Jim Wolper (wolp...@isu.edu) wrote:
: A true-life war story with a moral about GPS and
: navigation.
: Now comes the scary part.
: Two miles from the beacon the red WARN light on the GPS went on.
: It said 1.9NM all the way to touchdown. I believe what
All it takes to show you how much you can't count on GPS is get a good
handheld and take it everywhere for a week. I had a 4 failures last
week.
Last year GPS was usable almost 98% of the time.
P@Pilot
Yep! Had the same type of thing happen to me also. Except I was in day VFR
conditions. So, basically a non event as far as I'm concerned. In
mountainous regions, I trust my GPS as far as I can throw it.
-Pat
QFI Canadian Air Force
http://www.geocities.com/yosemite/4381
Paul Tomblin
In a previous article, tho...@not.abnormal.com (Tim Hogard) said:
>All it takes to show you how much you can't count on GPS is get a good
>handheld and take it everywhere for a week. I had a 4 failures last
>week.
I've flown approximately 75 hours with my Garmin GPSMAP-195 (and driven
probably three times that), and only had one failure, in the right seat on
final approach to Teterboro last Friday, which consisted of 2 interruptions of
about 10 seconds each. The pilot had a Garmin GPS-90, and his went out for
about 5 minutes, starting when mine first glitched for a few seconds.
--
Paul Tomblin (ptom...@xcski.com) I don't buy from spammers.
"A little rudeness and disrespect can elevate a meaningless interaction into a
battle of wills and add drama to an otherwise dull day."
- Calvin discovers Usenet
Marc Rodstein
On 30 Jan 1998 23:30:26 GMT, tho...@not.abnormal.com (Tim Hogard)
wrote:
>Jim Wolper (wolp...@isu.edu) wrote:
>: A true-life war story with a moral about GPS and
>: navigation.
>
>: Now comes the scary part.
>
>: Two miles from the beacon the red WARN light on the GPS went on.
>: It said 1.9NM all the way to touchdown. I believe what
>All it takes to show you how much you can't count on GPS is get a good
>handheld and take it everywhere for a week. I had a 4 failures last
>week.
>
>Last year GPS was usable almost 98% of the time.
>
>
>-tim
>http://web.abnormal.com
A handheld that is used with a portable antenna is like a fighter with
one hand behind his back. I used two different handhelds this way and
got lots of dropouts. Then I installed a permanent GPS antenna, and my
12 channel Garmin 195 has NEVER had a dropped signal over 250 hours
flying in the past 18 months.
Marc Rodstein
Boca Raton, FL
Dave Johnson
I'm interested in GPS in the IFR environment and would like to ask a couple
of questions ... first
In so far as Hailey (Sun Valley) has both a published GPS-A and GPS 31
approaches I would think that loss of signal due to terrain ... if on the
published approach ... would hardly be possible. How could the FAA certify
such an approach?
What type of GPS unit were you using. I have had poor experience with hand
held units, have had good experience with Narstar 5000 VFR panel mount
(with exception of when lithium battery went south), and NO experience with
an IFR certified panel mount.
Would request more info as to your altitudes. At 8000 (published) your not
really below much terrain except the 8826 to the NW and 8468 to the NE.
Always liked Hailey ... flew a few times out of there in the 70's, took
mountain instruction there, and will never forget going up to Smiley Creek
early one morning with instuctor for high density altitude TO and landings
on a downsloping runway. Great country!
--
David K. Johnson, xNYC, xUP, IATR
T-Arrow III N3064M, Seneca III N82073
EMail: cgwr...@netins.net
Jim Wolper <wolp...@isu.edu> wrote in article <34D1E9...@isu.edu>...
> A true-life war story with a moral about GPS and
> navigation.
>
> snip
gene...@ccp.com
> A handheld that is used with a portable antenna is like a fighter with
> one hand behind his back. I used two different handhelds this way and
> got lots of dropouts. Then I installed a permanent GPS antenna, and my
> 12 channel Garmin 195 has NEVER had a dropped signal over 250 hours
> flying in the past 18 months.
A handheld works quite well in my fabric covered TriPacer! But I agree
that a permanent antenna would be important in a metal coverd aircraft.
Gene
http://www.ccp.com/~geneseib/plane.html
-------------------==== Posted via Deja News ====-----------------------
http://www.dejanews.com/ Search, Read, Post to Usenet
Jim Wolper
Dave wrote:
>In so far as Hailey (Sun Valley) has both a published GPS-A and GPS 31
>approaches I would think that loss of signal due to terrain ... if on the
>published approach ... would hardly be possible. How could the FAA certify
>such an approach?Good question. Maybe Wally Roberts has a TERPS criterion? And, see
below. One of my points was that no ONE system alone will keep you
out of the rocks.
> What type of GPS unit were you using. I have had poor experience with hand
> held units, have had good experience with Narstar 5000 VFR panel mount
> (with exception of when lithium battery went south), and NO experience with
> an IFR certified panel mount.This is a King panel mount. I've never used n IFR one, either.
My Trimble handheld works very well except in one of our Senecas. One
of the guys I fly with has a handheld Garmin that works great except
in the same Seneca. We attribute this to that airplane's old
noisy radios. (But I was in a different one Thursday.)
> Would request more info as to your altitudes. At 8000 (published) your not
> really below much terrain except the 8826 to the NW and 8468 to the NE.
I was at 8000 and I that puts me below a _lot_ of
terrain. There's a 9532' 10 miles northeast, a 12009' 5 miles further,
9151' and 9728' to the northwest, etc. Any of these could have blocked a
GPS signal.
I have not investigated where the satellites were at that time, so this
is just conjecture.
> Always liked Hailey ... flew a few times out of there in the 70's, took
> mountain instruction there, and will never forget going up to Smiley Creek
> early one morning with instuctor for high density altitude TO and landings
> on a downsloping runway. Great country!
But Smiley Creek is an _easy_ one! There's enough room to fly a
pattern, and the turf is in excellent condition. The 7160' elevation
still gets your attention, doesn't it?
JSW
John Stephens
On Sat, 31 Jan 1998 00:29:43 GMT, ptom...@xcski.com (Paul Tomblin) wrote:
>In a previous article, tho...@not.abnormal.com (Tim Hogard) said:
>>All it takes to show you how much you can't count on GPS is get a good
>>handheld and take it everywhere for a week. I had a 4 failures last
>>week.
>
>I've flown approximately 75 hours with my Garmin GPSMAP-195 (and driven
>probably three times that), and only had one failure, in the right seat on
>final approach to Teterboro last Friday, which consisted of 2 interruptions of
>about 10 seconds each. The pilot had a Garmin GPS-90, and his went out for
>about 5 minutes, starting when mine first glitched for a few seconds.
I too have had only pone failure. It was on final into Toronto Buttonville
(KYKZ) in VMC when the tower had asked me to report a 5 mile final. Sure
enough, I lost staellite lock, and didn't notice that the GPS was no longer
counting down the distance until I was well within the requested 5 miles.
I screwed up the controllors sequencing with that little mistake, and he
,anaged to get two of us cleared to land while on short final. (In Canada
overlapping landing clearances is a no-no.)
Tim Hogard
Marc Rodstein (Rods...@worldnet.att.net) wrote:
: On 30 Jan 1998 23:30:26 GMT, tho...@not.abnormal.com (Tim Hogard)
: wrote:
: >Jim Wolper (wolp...@isu.edu) wrote:
: >: A true-life war story with a moral about GPS and
: >: navigation.
: >
: >: Now comes the scary part.
: >
: >: Two miles from the beacon the red WARN light on the GPS went on.
: >: It said 1.9NM all the way to touchdown. I believe what
: >All it takes to show you how much you can't count on GPS is get a good
: >handheld and take it everywhere for a week. I had a 4 failures last
: >week.
: >
: >Last year GPS was usable almost 98% of the time.
: >
: >
: >-tim
: >http://web.abnormal.com
: A handheld that is used with a portable antenna is like a fighter with
: one hand behind his back. I used two different handhelds this way and
: got lots of dropouts. Then I installed a permanent GPS antenna, and my
: 12 channel Garmin 195 has NEVER had a dropped signal over 250 hours
: flying in the past 18 months.
How many hours have you flow in the past 18 months? The reciver that
had the problem had 170 hrs since its last reset which was sometime
this year. Other GPS recivers have given me thousands of hours of logs
which show other problems.. Since its basicly the same reciver as the
one in your 195, I suspect that if your plane was where my car was, it
too would not have picked up enough sats for a position either. After
the second loss of signal, I turned off the unit, put it on top of the
car where there was a good view of the sky and then turned the unit
back on. It quickly found a solution using only 4 sats. Within a
minute one of the sats dropped out but the unit had picked up a sat on
the horizon so it kept the 3d fix. As soon as that sat was lost, it
lost track of its position. My old GPS 45 would not even get an inital
fix but it tends to stay off most of the time. If I had a GPS unit on
an airplane, I might have had a better lock on that sat on horizon or
even picked up a different one. One other fact is that I was quite
close to a known GPS jamming location (Near STL VOR).
Now for thouse that will claim the aircraft GPS is not the same as the
cheap handhelds...Check the chip set and schematic and then let me
know its not the same as my toy.
Now for more numbers...
The DOD service availbility in the year prior to sometime in Sep 1997 was
97.67%. That means GPS COULD NOT BE USED for over 204 hours. These are
DOD figures presented at the Civil GPS Interface Committee meeting in
Kansas City in Sep of 97.
Someone in the UK has seen over 30 failures of GPS units that are kept
in a nice safe lab with good antennas on the roof. The figure of
2000 MTBF was thrown out. VOR recivers have 10,000 MTBF.
So at this point counting on GPS is very risky.
Rod Farlee
Jim Wolper <wolp...@isu.edu> writes, regarding loss of GPS
coverage during the Hailey (SUN, Sun Valley ID) GPS approach:
>I was at 8000 and I that puts me below a _lot_ of terrain. There's a 9532'
>10 miles northeast, a 12009' 5 miles further, 9151' and 9728' to the
>northwest, etc. Any of these could have blocked a GPS signal.
The mountains NE (White Clouds) and NW (Sawtooths) are not a factor.
The GPS Block II/IIA orbits are 10,900 nm at 55 degrees inclination, so
they never get anywhere near the northern horizon. The hills alongside
the approach (E and W) shouldn't be factor until below MDA, and in the
visual segment.
This does give one pause, though, because the MDA is unusually high
due to rising terrain just past the airport. If the missed were initiated
late,
and GPS was then lost, and the pilot was unfamiliar, there's certainly a
scenario for a big problem.
The problem is in the GPS system itself. The specs are 98% service
availability and 98% coverage. VFR GPS users might not notice the
"RAIM holes" in coverage, caused by satellite geometry, but an IFR GPS
will. Any of us who have flown for long with GPS have seen GPS quit.
If/when WAAS is implemented, GPS may be up 99.9% of the time, maybe
as good as ILS. Meanwhile, GPS can only be relied on as a supplemental
means of navigation. It is just not reliable. Always have a backup plan, as
indeed you did!
- Rod Farlee
Victor Fraenckel
Tim Hogard (tho...@not.abnormal.com) wrote:
: Now for more numbers...
: The DOD service availbility in the year prior to sometime in Sep 1997 was
: 97.67%. That means GPS COULD NOT BE USED for over 204 hours. These are
: DOD figures presented at the Civil GPS Interface Committee meeting in
: Kansas City in Sep of 97.
: Someone in the UK has seen over 30 failures of GPS units that are kept
: in a nice safe lab with good antennas on the roof. The figure of
: 2000 MTBF was thrown out. VOR recivers have 10,000 MTBF.
: So at this point counting on GPS is very risky.
how many dropouts on handheld units were caused by the satellite system
and how many were caused by the receiver? dropouts are not NECESSARILY
caused by the satellite system. i suspect that to keep the costs down the
some realiability has been sacrificed. perhaps people are using these
units for tasks they were never designed to be used for. they are for
recreation use not precision approaches to runways. they do damn well for
the tasks they should be used for at the price they sell for.
--
regards
vic fraenckel
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Julian Scarfe
Tim Hogard wrote:
> Someone in the UK has seen over 30 failures of GPS units that are kept
> in a nice safe lab with good antennas on the roof. The figure of
> 2000 MTBF was thrown out. VOR recivers have 10,000 MTBF.
Not the ones in our aircraft! ;-) I'd be very interested to know some more
details. What exactly is an "F" for a VOR receiver, or for that matter a GPS?
In Europe, the risk management issues are not just academic. From the end of
April 98, all aircraft flying IFR at FL100 and above will be required to carry
area navigation equipment (BRNAV), and exactly what complies as BRNAV is a
burning issue. For a while, it looked as if GPS systems would not be approved
for the purpose. Now it looks like TSO C129a GPSs will be approved, which is
still stricter than the FAA's requirement for enroute. The only alternatives
are the vastly expensive DME/DME systems used by the airlines.
It's very laudable for the authorities to be concerned that GPS should be
absolutely infallible before it can be used in anger, but that ignores the
true risk involved in relying on currently approved systems. The true risk
should take into account the man-machine interface as well as the operational
alternatives.
For example, which is safer on a particular route: low level VFR in a single
in 1 mile visibility, or IFR at FL110 using "only" a TSO C129 GPS, along what
are, for the most part, VOR/NDB-defined airways? In May this year, the latter
may be illegal.
And I just can't reconcile the AICs that I have been sent, the one warning of
the inherent dangers of NDB approaches (and I agree) which are widespread in
the UK, the other implying that GPS approaches, even as overlays, will be a
long time coming. If I define a "failure" as an ADF needle indicating more
than 10 degrees off the correct relative bearing, we're talking a MTBF of
seconds, not 2000 hours.
To their credit, the authorities have got their act together and are starting
to make concessions, but I can't help wondering how many lives may be lost
because pilots are using outdated methods and technologies while the GPS
manufacturers struggle to make their products pass the seemingly arbitrary
criteria thrown up before them.
[BTW great original article, Jim]
--
Julian Scarfe
jf mezei
Julian Scarfe wrote:
> For example, which is safer on a particular route: low level VFR in a single
> in 1 mile visibility, or IFR at FL110 using "only" a TSO C129 GPS, along what
> are, for the most part, VOR/NDB-defined airways? In May this year, the latter
> may be illegal.
One aspect of GPS which causes "resistance" is that it is hard for the
user to know if the GPS is working correctly or not.
While situations such as the ship in the James Bond Movie are perhaps
exagerated, a failure in a GPS unit may not be "visible" until it is too
late. What if your GPS looses track of SVs but the error message is not
shown or not very obvious, and you continue to rely on your GPS thinking
all is well. Same could be said for a SV which might have gone funny.
I did read that the FAA in the USA were working towards adding to the
GPS system so that properly equipped receivers would/could be told to
dismiss a stray satellite, as well as providing proper corrolation
between a runway and where the GPS thinks it is. (similar to DGPS i
think).
Roy Smith
"[non-spam]jfmezei"@videotron.ca wrote:
> One aspect of GPS which causes "resistance" is that it is hard for the
> user to know if the GPS is working correctly or not.
As opposed to, say, a VOR?
Ron Natalie
Or an NDB?
Pete
> A true-life war story with a moral about GPS and
> navigation.
> Two miles from the beacon the red WARN light on the GPS went on.
> It said 1.9NM all the way to touchdown. I believe what
> happened is that as we flew into the valley we had loss of signal
> due to terrain masking of satellites. Just when I wanted
> the GPS the most, it failed.
>
> We made a safe and legal VFR approach nonetheless; we had
> the required visibility (even though we couldn't see *&&^$#%$;
> there are no obstruction lights on the mountains, so even
> with 10 miles visibility we couldn't see them 5 miles away)
> and followed the road which we both knew from long experience
> leads to the runway.
>
> The point? As Bowditch says, no prudent navigator relies on
> any one piece of navigational equipment. Back up that GPS with
> something, even if it's only dead reckoning. (And while you're
> at it, back up your hard drive, too.)
A really good story to back up the idea of keeping Loran C operational.
While the weather could possibly create dicey signal, it seems to me
having a seamless transitin from one form of radionav to another is a good
idea. This story will be forwarded to my Congressman, who will be voting
on continued Loran funding...pete
--
Surely you"re *smart* enough to remove the spam control...
Ryan R. Healy
John Stephens wrote:
> I too have had only pone failure. It was on final into Toronto Buttonville
> (KYKZ) in VMC when the tower had asked me to report a 5 mile final. Sure
> enough, I lost staellite lock, and didn't notice that the GPS was no longer
> counting down the distance until I was well within the requested 5 miles.
Everyone who has mentioned GPS unlocks may wish to check the GPS notams before
flight. Periodically, a notam will be published that states that the signal will
be unreliable within X number of miles of a particular airport, city or VOR. For
example, I will be flying to Washington DC tomorrow morning and there are two GPS
notams out for that time period that states that the signal will be unreliable
during the better part of the day in that area. What a bummer. Basically, all
this means however is that the integrity of the signal might not be as good as it
can be, but normally, when this is the case, the position is still accurate enough
to use for enroute navigation. Every once in a while, I will flip to the page that
displays position accuracy, and the most it has ever been, even during periods of
signal degradation is 3/4 of a mile. Unfortunately however, the GPS will not allow
GPS approaches to be conducted during periods of signal degradation. It comes up
with a "RAIM not available" message, and will not allow a GPS approach to be
conducted. Oh well. Back to basics, I guess....at least for tomorrow.
--
Blue Skies,
Ryan R. Healy
mailto:rhea...@sprynet.com
http://home.sprynet.com/sprynet/rhealy707
...1972 -- Watergate 1998 -- Zippergate
Julian Scarfe
jf mezei wrote:
> One aspect of GPS which causes "resistance" is that it is hard for the
> user to know if the GPS is working correctly or not.
I agree in part. But again, the comparison that's usually made is not
like-with-like. With most of the equipment that we use in flight, failure
modes are nothing like as secure as TSO C129's provisions:
Do you ever use an NDB without constantly listening to the ident? Have you
ever made an ADF approach near a thunderstorm? How carefully before every
flight do you check the little grub screw that holds the needle of the ADF
onto the bit that rotates? Have you ever seen a VOR indication that you knew
to be outside operational limits but no flag appeared? Have you ever dialled
the reciprocal track into your HSI for an ILS approach? Would all KNS80 users
who have never dialled in the wrong offset data please make themselves known
to the flight attendant? Oh yeah, and has anybody out there ever misidentified
a visual landmark? ;-)
I'm not saying that GPS is perfect in these regards, but let's not pretend
that what we use now is so secure we can never make mistakes. Over the years,
there have been too many aircraft pieces strewn across mountainsides to be
complacent.
--
Julian Scarfe
Roy Smith
justpete.n...@a.crl.com (Pete) wrote:
> A really good story to back up the idea of keeping Loran C operational.
> While the weather could possibly create dicey signal, it seems to me
> having a seamless transitin from one form of radionav to another is a good
> idea. This story will be forwarded to my Congressman, who will be voting
> on continued Loran funding...pete
Good knee-jerk reacion, but I'm not sure there's much logic in there.
The story was flying into what sounds like a steep narrow valley. I doubt
you would get much of a useful loran signal in an area like that. True,
it's not line of sight like GPS is, but it is effected by terrain.
--
Roy Smith <r...@popmail.med.nyu.edu>
New York University School of Medicine
550 First Avenue, New York, NY 10016
Gregory Travis
In article <roy-020298...@qwerky.med.nyu.edu>,
Roy Smith <r...@popmail.med.nyu.edu> wrote:
>justpete.n...@a.crl.com (Pete) wrote:
>> A really good story to back up the idea of keeping Loran C operational.
>> While the weather could possibly create dicey signal, it seems to me
>> having a seamless transitin from one form of radionav to another is a good
>> idea. This story will be forwarded to my Congressman, who will be voting
>> on continued Loran funding...pete
>
>Good knee-jerk reacion, but I'm not sure there's much logic in there.
>
>The story was flying into what sounds like a steep narrow valley. I doubt
>you would get much of a useful loran signal in an area like that. True,
>it's not line of sight like GPS is, but it is effected by terrain.
Actually, LORAN would have little trouble in a steep, narrow, valley. It's
affected by terrain only in that terrain can induce a slight positional
error due to increased propagation time. But, being a low-frequency system,
the signal doesn't much give a hoot if you're in the air, on the ground,
in a valley, under trees, or in a building. I can get my Flybuddy
LORAN to lock onto the southeastern &/or northeastern LORAN chains
while I'm sitting in my all-metal enclosed hangar with the door closed
in southern Indiana.
My GPS won't get a lock on any satellites inside my all-wooden home
just a few miles away.
Frankly, I would rather have a possible 1000' of positional error,
on the missed, than no course guideance at all.
greg
Pete
In article <roy-020298...@qwerky.med.nyu.edu>,
r...@popmail.med.nyu.edu (Roy Smith) wrote:
> justpete.n...@a.crl.com (Pete) wrote:
> > A really good story to back up the idea of keeping Loran C operational.
> > While the weather could possibly create dicey signal, it seems to me
> > having a seamless transitin from one form of radionav to another is a good
> > idea. This story will be forwarded to my Congressman, who will be voting
> > on continued Loran funding...pete
>
> Good knee-jerk reacion, but I'm not sure there's much logic in there.
Clearly you don't understand how Loran signals are propagated. They are
very low frequency and thus follow terrain quite well, just like AM radio.
I've used Loran C for 10 years and I can tell you it would not have lost
all signal in the area described. I have *flown* in that area and the
accuracy was excellent all the way to the ground.
Have *you* *ever* flown there?...Doctor?...pete
Knee jerk my ass
Roy Smith
justpete.n...@a.crl.com (Pete) wrote:
> Clearly you don't understand how Loran signals are propagated.
Actually, I do know quite a bit about it, but to get to the point of this
post...
My apologies for using the term "knee jerk". That was a extremely poor
choice of words. Not quite sure what caused me to type that.
Reece R. Pollack
On 2 Feb 1998 09:54:01 -0500, gr...@sherrill.kiva.net (Gregory Travis)
wrote:
>Actually, LORAN would have little trouble in a steep, narrow, valley. It's
>affected by terrain only in that terrain can induce a slight positional
>error due to increased propagation time. But, being a low-frequency system,
>the signal doesn't much give a hoot if you're in the air, on the ground,
>in a valley, under trees, or in a building. I can get my Flybuddy
>LORAN to lock onto the southeastern &/or northeastern LORAN chains
>while I'm sitting in my all-metal enclosed hangar with the door closed
>in southern Indiana.
>
>My GPS won't get a lock on any satellites inside my all-wooden home
>just a few miles away.
True, but will your LORAN lock on when there's a lot of precipitation?
P-static will do a number on LORAN signals, while the frequencies for
GPS were selected specifically to avoid such effects.
It's also pretty rare to be flying inside any sort of building, or
under dense foliage. It's also unlikely that you would have a
certified GPS approach in a valley deep and narrow enough to block GPS
signals. After all, most of the satellites are going to be a good ways
above the horizon.
>Frankly, I would rather have a possible 1000' of positional error,
>on the missed, than no course guideance at all.
They started out certifying LORAN approaches until they discovered
that they weren't workable. I'd love to keep LORAN as an enroute
backup, but I don't think you'll ever see LORAN approaches.
--
Reece R. Pollack
CP-ASMEL-IA -- N1707H Piper Arrow III (based GAI)
Reece R. Pollack
>One aspect of GPS which causes "resistance" is that it is hard for the
>user to know if the GPS is working correctly or not.
That's the big reason that handhelds are not usable for IFR, and why
TSO 129 units are. A TSO 129 unit must have RAIM, which is Receiver
Autonomous Integrity Monitoring. A unit using RAIM uses additional
satellites to verify the positional solution. There is one standard
for enroute and terminal operations, and another, tighter standard for
approach operations. It's quite possible for a TSO 129a receiver to
flag on approach, yet unflag on the missed due to the differing
standards.
>While situations such as the ship in the James Bond Movie are perhaps
>exagerated, a failure in a GPS unit may not be "visible" until it is too
>late. What if your GPS looses track of SVs but the error message is not
>shown or not very obvious, and you continue to rely on your GPS thinking
>all is well. Same could be said for a SV which might have gone funny.
Believe me, a TSO 129a GPS makes it obvious. My King KLN-89B displays
a standard flag in the CDI, just like a VOR, and the CDI display on
the unit says "*F*L*A*G*" in big letters, with the asterisks.
I know an avionics tech who happened to be installing a VFR-only GPS
receiver in a plane the day a satellite went astray. He knew something
was amiss because the GPS insisted that it had a valid position, only
that position was in southern California and he was in Virginia. When
he tried a Garmin 155 (a TSO 129a unit), it immediately reported the
problem, as did a TSO'ed King unit. The VFR-only unit continued to
happily report itself in SoCal.
At the same time my friend was having his trouble, an FAA Flight Check
plane was testing several new TSO 129a GPS receivers. All flagged but
one. Since they couldn't finish their tests, they decided to follow
the unflagged unit's indications (it was VMC). When they were 70nm
from where they should have been they gave up. Needless to say the bad
unit lost its TSO until the problem was corrected.
>I did read that the FAA in the USA were working towards adding to the
>GPS system so that properly equipped receivers would/could be told to
>dismiss a stray satellite, as well as providing proper corrolation
>between a runway and where the GPS thinks it is. (similar to DGPS i
>think).
You need 4 satellites to get a valid 3D position. With a 5th you can
identify any single failure. With a 6th it's theoretically possible to
determine which satellite has failed. Current TSO 129a units will
identify a failure but will not remove the failed satellite even if
there are enough available to do so. Future units (under later TSO's)
may do so. The ability to incorporate corrections from ground-based
transmitters is DGPS. Even my ancient Garmin 95XL can accept DGPS
corrections, if you supply an external receiver.
MLopata
no.spam Pete writes:
>Clearly you don't understand how Loran signals are propagated. They are
>very low frequency and thus follow terrain quite well, just like AM radio.
>I've used Loran C for 10 years and I can tell you it would not have lost
>all signal in the area described. I have *flown* in that area and the
>accuracy was excellent all the way to the ground.
>Have *you* *ever* flown there?...Doctor?...pete
>Knee jerk my ass
Pete,
Don't you think you are a bit harsh with your judgements and opinions? Perhaps
you are an expert user of Loran C - perhaps not. I am not (I prefer using a
bubble sextant and doing real-man navigation), but I have been using Loran C
since I had to use an oscilloscope to manually align the square-wave signals
(circa 1980), and I do know a bit about the theory involved. "Clearly" you do
not. According to the USCG (who aughta know) Loran C, in the vicinity of Sun
Valley, will provide accuracy of only 200 to 700 feet, based on ground-wave
propagation theory; regardless of how flat the land or unflat is (you were
right about that). Accuracy is even worse within 1-2 TS's of the chain
baselines, although I do not know where SUN falls in the regard. GPS, on the
other hand, theoretically provides uniform accuracy always at the low end of
the Loran accuracy range, regardless of geographic position, provided the SV
geometry is favorable. Argueably (i.e., clearly) the FAA would have a Loran C
approach into SUN if it felt the signals were sufficiently accurate, but 700
feet at the MM doesn't thrill me much. Perhaps you have just been lucky with
your Loran C. I find it hard to believe that, over the numbers of a 100 ft
wide runway, and a best stated accuracy of 200 ft horizontally, your excellent
accuracy "all the way to the ground" is anything but a fluke or your
imagination. In any event, even though you have the right to say what you want
about anyone (except me, of course), it would be really nice if I could find
just 1 aviation NG where people behaved with even a small measure of courtesy.
If Roy is in fact a doctor (he could be a Student, Chancellor, or Building
Superintendent for all you know) how would you feel if you ended up on his
operating table some time after you crashed into the Empire State Building
because you relied on your Loran C too much and he remembered your
mean-spirited post?? (I think NYU puts email names on those little plastic
bracelets now.) Kiss and make up.
-Marc
Roy Smith
re...@his.com (Reece R. Pollack) wrote:
> They started out certifying LORAN approaches until they discovered
> that they weren't workable. I'd love to keep LORAN as an enroute
> backup, but I don't think you'll ever see LORAN approaches.
The funny thing about LORAN is that while the raw accuracy of the system
isn't so hot, the majority of the positional error is systemic, i.e. you
can measure it and cancel it out. Has to do with the fact that the
signals propigate at different velocities over different types of terrain.
This "measure and cancel out" principle is exactly the same as the idea
behind differential GPS, except that with GPS, the dithering changes on a
minute-to-minute basis, while with Loran, the error is essentially
constant (although I'll be it varies at least somewhat with things like
recent rainfall history and water table height). This makes it possible
to do long-term corrections, and from what I can see of the few Loran-RNAV
approaches I've seen, this is exactly what they were planning on doing --
plugging in W, X, Y, and Z corrections.
It is well known (at least among people who actually understand how this
stuff works) that while the raw accuracy of GPS may be better than Loran,
the repeatability of Loran positions is better than GPS (at least GSP with
SA turned on). That means that if you go to a spot record the TD
coordinates, and then go back later to a place where the TDs are the same,
you'll be right where you were the first time. This is what fisherman
usually do to find that magic spot again.
You may not know the exact lat/long, but you'll know you're back in the
same spot, which often is all that matters. It is certainly all that
matters for an instrument approach.
Reece is also correct about the problems GPS has with being line-of-sight,
and not working inside buildings, under dense foliage, etc. The only time
I've ever flown an airplane through a hangar is on a flight simulator, so
I don't consider GPS performance under those conditions to be too critical
a factor. Same goes for marine navigation. I do wonder about those GPS
systems they are putting into cars, though. Cars go under bridges,
through tunnels, drive down narrow tree-canopy-shrouded roads, and drive
in urban canyons. All of those sound like places where GPS will have
trouble working well, but none of those are considerations for aviation
use.
I really do feel for those people who have invested in aviation loran
systems, but overall the utility of the GPS system is so much greater than
loran, it's just hard to justify putting much money into keeping the loran
stuff going.
Roy Smith
mlo...@aol.com (MLopata) wrote:
> If Roy is in fact a doctor (he could be a Student, Chancellor, or Building
> Superintendent for all you know)
Actually, I'm just a computer guy working in the School of Medicine.
> I think NYU puts email names on those little plastic bracelets now.
Hah! I wish the hospital end of things were so enlightened when it came
to modern computer technology that this was true! I would say more about
that, but I like my job and would like to keep it a little bit longer...
I keep telling OB/GYN we should have one of our guys in the delivery room
setting up new email accounts as the first order of business, but they
don't listen to me.
Gregory Travis
In article <roy-030298...@qwerky.med.nyu.edu>,
Roy Smith <r...@popmail.med.nyu.edu> wrote:
>re...@his.com (Reece R. Pollack) wrote:
>> They started out certifying LORAN approaches until they discovered
>> that they weren't workable. I'd love to keep LORAN as an enroute
>> backup, but I don't think you'll ever see LORAN approaches.
>This "measure and cancel out" principle is exactly the same as the idea
>behind differential GPS, except that with GPS, the dithering changes on a
>minute-to-minute basis, while with Loran, the error is essentially
>constant (although I'll be it varies at least somewhat with things like
>recent rainfall history and water table height). This makes it possible
>to do long-term corrections, and from what I can see of the few Loran-RNAV
>approaches I've seen, this is exactly what they were planning on doing --
>plugging in W, X, Y, and Z corrections.
Of course, the differential principles being developed for GPS
could be used for LORAN as well.
>It is well known (at least among people who actually understand how this
>stuff works) that while the raw accuracy of GPS may be better than Loran,
>the repeatability of Loran positions is better than GPS (at least GSP with
>SA turned on). That means that if you go to a spot record the TD
>coordinates, and then go back later to a place where the TDs are the same,
>you'll be right where you were the first time. This is what fisherman
>usually do to find that magic spot again.
>You may not know the exact lat/long, but you'll know you're back in the
>same spot, which often is all that matters. It is certainly all that
>matters for an instrument approach.
>I really do feel for those people who have invested in aviation loran
>systems, but overall the utility of the GPS system is so much greater than
>loran, it's just hard to justify putting much money into keeping the loran
>stuff going.
We can keep both systems by investing about 2% of the GPS operating
budget in LORAN. For a separate and complimentary system that provides
similar service and accuracy that would seem to be a real bargain price
from a redundancy standpoint alone.
Countries other than the United States (yes, they exist) are investing heavily
in updating their LORAN systems. Furthermore, a real political (and
fiscal) advantage of LORAN is that using nations underwrite their own
navigation capability. Right now, France (to pick a nation at random) gets
to navigate via GPS at the United State's expense (the horror).
As for the United States, LORAN costs about $10 million a year to maintain.
GPS costs up to $500 million a year to maintain. That's five times an
order of magnitude more for systems that, in their "raw" modes don't perform
more than an order of magnitude apart (GPS will get you within 300' of
a spot 95% of the time, LORAN will get you within 2000' of a spot
95% of the time). If you consider repeatability as the benchmark (which it
should be for aviation use), LORAN already beats GPS out of the stall
(as Roy points out). Applying differential technology to LORAN narrows
the positional accuracy gap even further.
For non-aviation civilian users, LORAN would appear superior to GPS also. As
Roy pointed out, LORAN is a lot less likely than GPS to lose position in
a city, or a tunnel, under a bridge, along a tree-lined road, etc. LORAN,
of course, is also a lot harder to jam than is GPS.
greg, certified LORAN bigot.
Roy Smith
gr...@sherrill.kiva.net (Gregory Travis) wrote:
> We can keep both systems by investing about 2% of the GPS operating
> budget in LORAN.
Hmmm. Interesting. I just did some *very* rough back-of-the-envelope
calculations and come up with the coverage area of the Continental US
Loran system being, guess what, about 2% of the Earth's surface! That
doesn't count the Alaska chain. Add in that, round some stuff up, count
coastal oceanic areas, maybe you get up to 3%. Looks like Loran and GPS
cost, at least at first glance, about the same to run per square mile of
coverage.
The problem is, with Loran, we just pay for the part we use. With GPS, we
pay for it all. So, the obvious solution is to have the rest of the world
chip in their fair share. Don't suppose there's much chance of that
happening. It would be far too logical.
So, what do you get with GPS, that you don't get with Loran? Well, you
get offshore ocanic coverage, for one (with Omega shut off, GPS is the
only game in town). You also get 3-D positioning (even if it's pretty
sloppy in the Z-direction as things stand now).
GPS is also a lot less sensitive to single points of failure. Some parts
of the coverage are are adequately covered by multiple chains, or multiple
master-slave pairs, but there are lots of places with sub-optimum geometry
where a single slave going off the air could effectively shut down the
system. And, of course, if a master goes off the air, the whole chain is
down. Keep in mind that a typical transmitter is often both a slave for
one chain and a master for another.
> GPS will get you within 300' of a spot 95% of the time
That's with SA on. Turn SA off, and you get the 95% zone down to a
fraction of that. And differential will do better. And, yes, you could
do differential Loran, but I don't know of any efforts to actually do
that.
> For non-aviation civilian users, LORAN would appear superior to GPS also.
Well, there's problems there too. For one, Loran needs a fairly large
antenna. A typical marine Loran antenna is about a meter long. Aviation
loran antennas seem to work fine with much shorter lengths, but they are
still about 1/4 meter long, or longer. That makes for real logistical
problems trying to make portable units.
Loran also seems to be susceptable to RFI. I've been on boats where the
Loran set didn't work right if, for example, electronic-ballest
flourescent lights were turn on.
> LORAN of course, is also a lot harder to jam than is GPS.
Why do you say that?
David Lesher
r...@popmail.med.nyu.edu (Roy Smith) writes:
>So, what do you get with GPS, that you don't get with Loran? Well, you
>get offshore ocanic coverage, for one (with Omega shut off, GPS is the
>only game in town). You also get 3-D positioning (even if it's pretty
>sloppy in the Z-direction as things stand now).
You get the time. Most cellular telephone sites use GPS as a time
reference. It {I am told} offers orders of magnitude better accuracy
than LF/HF WWVB/WWV.
Not sure pilots need this, but many other things do....
>Loran also seems to be susceptable to RFI. I've been on boats where the
>Loran set didn't work right if, for example, electronic-ballest
>flourescent lights were turn on.
Amen....
>> LORAN of course, is also a lot harder to jam than is GPS.
>Why do you say that?
I'd agree. LORAN is easy to jam in a region. Read "Secret War" by
Brian ?Wilson? re: RVJones and jamming NAZI "beam" systems...
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
Gregory Travis
>> We can keep both systems by investing about 2% of the GPS operating
>> budget in LORAN.
>
>Hmmm. Interesting. I just did some *very* rough back-of-the-envelope
>calculations and come up with the coverage area of the Continental US
>Loran system being, guess what, about 2% of the Earth's surface! That
>doesn't count the Alaska chain. Add in that, round some stuff up, count
>coastal oceanic areas, maybe you get up to 3%. Looks like Loran and GPS
>cost, at least at first glance, about the same to run per square mile of
>coverage.
>
>The problem is, with Loran, we just pay for the part we use. With GPS, we
>pay for it all. So, the obvious solution is to have the rest of the world
>chip in their fair share. Don't suppose there's much chance of that
>happening. It would be far too logical.
It would also be a technology and bureaucratic nightmare. How are you
proposing that it be enforced? We somehow "require" Iraq (or whatever
the demonized country of the day is) to pay royalties to the United States
for GPS use? We require each country to police ALL of its various GPS
receiver manufacturers so that they pay a licensing fee per receiver
sold? Well, I guess it will give the DEA another good excuse to go busting
down people's doors at night. "GPS police!"
>So, what do you get with GPS, that you don't get with Loran? Well, you
>get offshore ocanic coverage, for one (with Omega shut off, GPS is the
>only game in town). You also get 3-D positioning (even if it's pretty
>sloppy in the Z-direction as things stand now).
Loran already extends several hundred miles out to sea (i.e. to the
fisheries where it's needed). Somehow, boats have been doing a pretty
good job of crossing the ocean without GPS for, oh, six or more centuries.
>GPS is also a lot less sensitive to single points of failure. Some parts
>of the coverage are are adequately covered by multiple chains, or multiple
>master-slave pairs, but there are lots of places with sub-optimum geometry
>where a single slave going off the air could effectively shut down the
>system. And, of course, if a master goes off the air, the whole chain is
>down. Keep in mind that a typical transmitter is often both a slave for
>one chain and a master for another.
I can recieve at least three different chains here in Indiana. There would
have to be a whole lot of failure to knock my LORAN nav capability out.
Of course, for another 2% of the GPS budget you could absolutely pollute
the countryside with redundant LORAN transmitters.
On the other hand, 3-D RAIM requires that you see at least six satellites
at all times in order to guarantee that the loss of a single one doesn't
wipe out your nav capability. How much of a margin does that leave?
And, of course, the GPS system has several single points of failure. One
is located in Colorado.
>> GPS will get you within 300' of a spot 95% of the time
>
>That's with SA on. Turn SA off, and you get the 95% zone down to a
>fraction of that.
And SA is currently...?
>And differential will do better. And, yes, you could
>do differential Loran, but I don't know of any efforts to actually do
>that.
Because we've got far better things to spend $490 million dollars a year
on than implement differential LORAN and/or solve any lingering P-static
problems with the system. By the way, my seven year old $1000.00 FlyBuddy
VFR LORAN has NEVER lost signal in the rain and I used to fly some pretty
wicked IFR. If it did, I would go ahead and add static wicks to my plane.
I'll grant that it might be more a P-static problem in faster aircraft or
in more "winterly" conditions than those under which I usually fly.
>Loran also seems to be susceptable to RFI. I've been on boats where the
>Loran set didn't work right if, for example, electronic-ballest
>flourescent lights were turn on.
>
>> LORAN of course, is also a lot harder to jam than is GPS.
>
>Why do you say that?
Power and frequency at which the LORAN signals are transmitted. GPS
signals are below background noise. LORAN transmitters are several
kilowatts. There is a russian company making a GPS jammer, for about
$4000.00, that will take out all GPS service within hundreds of miles.
greg
David M Parrish
>As for the United States, LORAN costs about $10 million a year to maintain.
>GPS costs up to $500 million a year to maintain. That's five times an
I think LORAN is an excellent backup to GPS as the primary navigation system.
Both have very good economies of scale and the failure modes of one don't
effect the other. Both are even accurate enough for some IFR approaches.
(Since LORAN has an relatively poor absolute accuracy, but very good
repeatability, LORAN runway coordinates in the database could be 'fudged' for
better accuracy. Without differential signals.)
>a city, or a tunnel, under a bridge, along a tree-lined road, etc. LORAN,
>of course, is also a lot harder to jam than is GPS.
Interestingly, the reason GPS signals are intentionally below the noise floor
was to make it un-jamable. (If that's really true, then why are there
government run GPS jamers in several locations of this country?)
If you're really a nail bitter and have a reasonable technical bent, go check
the links to Keith Peshack's web page from Jim Weir's pages. Interesting
comparisons between GPS and the Russian Glonast(?).
---
David Parrish
Roy Smith
wb8...@netcom.com (David Lesher) wrote:
> You get the time. Most cellular telephone sites use GPS as a time
> reference. It {I am told} offers orders of magnitude better accuracy
> than LF/HF WWVB/WWV.
Orders of magnitude better than WWV? That I greatly doubt!
Ron Natalie
Roy Smith wrote:
>
> wb8...@netcom.com (David Lesher) wrote:
> > You get the time. Most cellular telephone sites use GPS as a time
> > reference. It {I am told} offers orders of magnitude better accuracy
> > than LF/HF WWVB/WWV.
>
> Orders of magnitude better than WWV? That I greatly doubt!
>
I don't think it's the accuracy so much as the convenience.
First you have to receive the WWV signal, which is a pain
in the butt in someplaces, second you have to lock to it
with what ends up being analog equipment. With GPS all you
have to do is be able to see the sky and you can pull time
digitally out of any cheap GPS receiver.
David Lesher
r...@popmail.med.nyu.edu (Roy Smith) writes:
>wb8...@netcom.com (David Lesher) wrote:
>> You get the time. Most cellular telephone sites use GPS as a time
>> reference. It {I am told} offers orders of magnitude better accuracy
>> than LF/HF WWVB/WWV.
>Orders of magnitude better than WWV? That I greatly doubt!
I don't. HF propagation is very irregular. And since the GPS
receiver knows [duh!] where it is, it can offset the delay in
getting the signal from the bird to you.
Mind you, I can not recall the real numbers, but I'm sure they are
findable.
MLopata
Gregory Travis writes:
>>My GPS won't get a lock on any satellites inside my all-wooden home
>just a few miles away.
GPS requires a direct line-of-sight to any tracked SV's. The only signals you
might receive inside your house will be multipath reflextions.
Gregory Travis
Gregory Travis
In article <19980204024...@ladder02.news.aol.com>,
MLopata <mlo...@aol.com> wrote:
>David Lesher writes:
>
>>You get the time. Most cellular telephone sites use GPS as a time reference.
>>It {I am told} offers orders of magnitude better accuracy than LF/HF
>>WWVB/WWV.
>
>
>(real-time kinematic) DGPS for use on one of my projects and I noticed that the
>time signal was about 10 seconds FASTER than WWV. The latency of the receiver
>is 20 ms and I had it set to 10 Hz upgrades, so go figure! Any ideas about
>that?
WWV and the GPS clock are set to different standards. Don't have the info
in front of me but the fact that they differ by ~10 seconds is not a
function of propagation delay. It's a function of what they're
referencing.
Was it Einstein who said "A man with one watch knows what time it is, a
man with two watches is never sure?"
greg
Gregory Travis
>
>>As for the United States, LORAN costs about $10 million a year to
>>maintain. GPS costs up to $500 million a year to maintain. That's five times
>>perform more than an order of magnitude apart (GPS will get you within 300'
>>of a spot 95% of the time, LORAN will get you within 2000' of a spot
>>95% of the time).
>
>The scope of this whole GPS/Loran discussion is too narrow for words. You are
>hitting on the real use of GPS, and general aviation aint it. Surveyors and
>others that demand 1/100 foot accuracy use GPS with far more dollar-frequency
>than us pilots. Survey-grade units, which I also use to navigate underwater
>vehicles, guarantee accuracy of 9/10 of a centimeter. Loran couldn't touch
>that in a million years. GA is just a happy bystander to something that the
>DoD is letting them use.
Two questions:
1. How do you use GPS underwater
2. What kind of lobby does the "1/100 foot" surveyors
association have to justify a $500million/year system
for, what, 10,000 surveyors?
greg
Dave Katz
mlo...@aol.com (MLopata) writes:
> >You get the time. Most cellular telephone sites use GPS as a time reference.
> >It {I am told} offers orders of magnitude better accuracy than LF/HF
> >WWVB/WWV.
This is absolutely true.
> Interesting comment, David. Recently I was calibrating an Ashtech Z-12 RTK
> (real-time kinematic) DGPS for use on one of my projects and I noticed that the
> time signal was about 10 seconds FASTER than WWV. The latency of the receiver
The 10 second difference (probably a few seconds more than this) is most
likely the difference between unadjusted GPS time and UTC--the difference
being the leap seconds that have been added since the GPS timescale was
established. The current leap second count is carried somewhere in
the GPS messages, so most receivers make this adjustment automatically.
> is 20 ms and I had it set to 10 Hz upgrades, so go figure! Any ideas about
> that?
>
> As for that "order of magnitude," are we talking that order as 10e-9 or so?
Yep, somewhere around there. GPS time is used for precision time
synchronization in quite a few applications; microsecond accuracy
relative to UTC is achievable even with selective availability.
The frequency is stable enough so that the phone companies use it to
discipline the clocking used throughout the system.
WWV's accuracy is limited by factors such as the propagation delay
and the height of the ionosphere--these factors are quite large
relative to the accuracy gained by GPS time.
GPS is by far the best timekeeping you'll ever get, short of having your
own cesium atomic clock (and even then you'll have to take it over
to the US Naval Observatory for periodic adjustment).
Sam Nelson
In article <34D4EF...@videotron.ca>, jf mezei <"[non-spam]jfmezei"@videotron.ca> writes:
| Julian Scarfe wrote:
| > For example, which is safer on a particular route: low level VFR in a single
| > in 1 mile visibility, or IFR at FL110 using "only" a TSO C129 GPS, along what
| > are, for the most part, VOR/NDB-defined airways? In May this year, the latter
| > may be illegal.
|
| One aspect of GPS which causes "resistance" is that it is hard for the
| user to know if the GPS is working correctly or not.
|
of what result you're _supposed_ to get, you can't interpret its validity
when you get it. He who trusts his compass all the time has never climbed
in the Cuillins.
--
SAm. (Insert bandwidth-wasting disclaimer here)
Your Mileage May Vary... ...until they switch SA off, at least
MLopata
MLopata
Roy Smith writes:
>Aviation
loran antennas seem to work fine with much shorter lengths, but they
>are still about 1/4 meter long, or longer. That makes for real logistical
Roy, something came across my desk today for a GPS antenna that is about one
inch square and 1/8 inch thick. It can mount on a printed circuitboard. Hard
to argue with that.
MLopata
David Lesher writes:
>You get the time. Most cellular telephone sites use GPS as a time reference.
>It {I am told} offers orders of magnitude better accuracy than LF/HF
>WWVB/WWV.
Interesting comment, David. Recently I was calibrating an Ashtech Z-12 RTK
(real-time kinematic) DGPS for use on one of my projects and I noticed that the
time signal was about 10 seconds FASTER than WWV. The latency of the receiver
Paul Tomblin
In a previous article, gr...@sherrill.kiva.net (Gregory Travis) said:
>In article <19980204024...@ladder02.news.aol.com>,
>MLopata <mlo...@aol.com> wrote:
>>hitting on the real use of GPS, and general aviation aint it. Surveyors and
>>others that demand 1/100 foot accuracy use GPS with far more dollar-frequency
>>than us pilots. Survey-grade units, which I also use to navigate underwater
> association have to justify a $500million/year system
> for, what, 10,000 surveyors?
Civilian users of GPS, either GA or surveyors, don't pay for GPS. The US
military thinks it's worth $500million/year to gave the ability to navigate
and put bombs on the target anywhere in the world. The fact that it is useful
to other people besides the US military is just a nice side benefit. We don't
have to worry about who else uses it and make them pay for it - it's a
military system and the military will continue to pay for it whether the
entire world uses it or only them. As a consequence, don't expect the
military to make any changes to the system that would degrade its usefulness
to the military. They'll just say "It doesn't meet your needs? Tough shit.
Put up your own system." On the other hand, if they can make the changes
needed by GA or surveyors or whatever other user needs it *without* degrading
it's functionality to the military, they'll probably do it for the budgetary
brownie points providing it doesn't cost too much.
--
Paul Tomblin (ptom...@xcski.com) I don't buy from spammers.
"A little rudeness and disrespect can elevate a meaningless interaction into a
battle of wills and add drama to an otherwise dull day."
- Calvin discovers Usenet
a. m. boardman
Reece R. Pollack <re...@his.com> wrote:
>They started out certifying LORAN approaches until they discovered
>that they weren't workable. I'd love to keep LORAN as an enroute
>backup, but I don't think you'll ever see LORAN approaches.
There are (or at least were quite recently, I've got them in front of me)
a pair of LORAN approaches to BTV in the NOS NE-1 book, complete with a
TD correction chart in the back of the book. They've been there for
several years, even though so far as I know there has never been an
approach-approved LORAN receiver in the US.
Anyone know if the specs are still in the TERPS? I'm quite curious about
the clearance requirements for these things, given the current debate and
the fact that the straight-in minimums on the LORAN Rwy 15 approach are
only 513 HAA and 2400 RVR...
andrew,
who almost paid $150 for a handheld LORAN box about 10 years ago... I
paid twice as much for my GPS-90, but wouldn't trade for anything.
Roy Smith
gr...@sherrill.kiva.net (Gregory Travis) wrote:
> 2. What kind of lobby does the "1/100 foot" surveyors
> association have to justify a $500million/year system
> for, what, 10,000 surveyors?
I think you miss the point. No one use of GPS alone could justify the
cost (OK, maybe except the asinine Star Wars scheme which got it going).
Besides civil aviation and military uses, GPS is used for:
Marine navigation, ranging from oceanic to harbor pilotage.
Ground navigation systems for trucking companies (and now, consumers).
Time reference.
Surveying.
Geological measurements (like fault slippage). Well, OK, maybe that's a
subset of surveying.
I'm sure I've missed a few. Of these, I'd guess that Marine navigation is
by far the biggest civilian market. The number of ships in commercial
service vastly outnumbers the number of commercial aircraft, and the
number of recreational boats probably outnumbers GA aircraft 100 to 1 (if
not more). And for all the hooting about precision approaches, marine
uses require just as much accuracy. There's lots of twisty little
channels in small harbors where if you're off by 150 feet, you're aground.
Loran is/was used for many or all of these, but the convenience of GPS
equipment, combined with the increased raw accuracy, is what's driving
Loran out of the market. Yes, you can make a perfectly valid argument
that it still has uses, and a user community, but the size of that user
community is declining rapidly. The number of new Loran sets sold in the
last couple of years is infintesimal, and looking around, I see a lot of
older, but still perfectly serviceable, lorans being pulled out of boats
and planes and replaced by GPS. We are quickly reaching the point where,
even if the cost of running the loran system is 1/50th the cost of running
GPS, the cost per user is going to be higher.
Marc E* Zorn
Paul Tomblin wrote:
> Civilian users of GPS, either GA or surveyors, don't pay for GPS.
I beg to differ. You speak of the military as though it's is a self-funded
organization. Everyone who pays federal income tax is funding GPS in part.
-- Marc
David Lesher
>Paul Tomblin wrote:
"We don't pay" here really means "we don't have an option not to
pay.." If we do not use it; we still pay for it.
Paul Tomblin
In a previous article, zo...@mailsrv1.trw.com said:
>Paul Tomblin wrote:
>
>> Civilian users of GPS, either GA or surveyors, don't pay for GPS.
>
>I beg to differ. You speak of the military as though it's is a self-funded
>organization. Everyone who pays federal income tax is funding GPS in part.
I speak of the military as an organization that has control over how it spends
its own budget. In some respects it does. When it asks Congress for $500M
for GPS, it does so because it's worth $500M to the military for the military
uses of GPS, not because it's worth $20M to US civil aviation, plus $10M to US
surveyors, say. If the GPS wasn't worth $500M to the military, they would ask
for some or all of its budget to come out of other parts of the budget, such
as the FAA or the NOAA. But the military wants to keep complete control over
GPS, so they are the ones running it, and they are the ones fighting for its
budget (and making concessions on other military spending to keep it fully
funded).
--
Paul Tomblin (ptom...@xcski.com) I don't buy from spammers.
"Tower zero one request clearance for takeoff."
"Cleared runway three contact ground point six three when off the runway."
- Michael Crichton destroys whatever technical credibility he had left.
Marc Rodstein
On 31 Jan 1998 13:24:30 GMT, "Dave Johnson" <cgwr...@netins.net>
wrote:
>I'm interested in GPS in the IFR environment and would like to ask a couple
>of questions ... first
>
>In so far as Hailey (Sun Valley) has both a published GPS-A and GPS 31
>approaches I would think that loss of signal due to terrain ... if on the
>published approach ... would hardly be possible. How could the FAA certify
>such an approach?
>
>What type of GPS unit were you using. I have had poor experience with hand
>held units, have had good experience with Narstar 5000 VFR panel mount
>(with exception of when lithium battery went south), and NO experience with
>an IFR certified panel mount.
>
>Would request more info as to your altitudes. At 8000 (published) your not
>really below much terrain except the 8826 to the NW and 8468 to the NE.
>
>Always liked Hailey ... flew a few times out of there in the 70's, took
>mountain instruction there, and will never forget going up to Smiley Creek
>early one morning with instuctor for high density altitude TO and landings
>on a downsloping runway. Great country!
>
>--
>David K. Johnson, xNYC, xUP, IATR
>T-Arrow III N3064M, Seneca III N82073
>EMail: cgwr...@netins.net
>
>Jim Wolper <wolp...@isu.edu> wrote in article <34D1E9...@isu.edu>...
>> A true-life war story with a moral about GPS and
>> navigation.
>>
>> snip
Those of you who are using handhelds should not be disappointed with
GPS outages unless you have an external aircraft antenna. The "antenna
in the windshield" is always blocked from seeing a portion of the sky
by the airframe. It is amazing that it works as well as it does, but
it frequently cannot see enough satellites.
I have an external roof top antenna on 2 different planes, and a 12
channel GPS-195. I never get outages, not one, in 400 hours of flying
over 18 months.
Marc Rodstein
Boca Raton, FL
David Price
In article <34d46...@news.wizvax.net>, vic...@wizvax.net says...
>
>Tim Hogard (tho...@not.abnormal.com) wrote:
>: Now for more numbers...
>: The DOD service availbility in the year prior to sometime in Sep
1997 was
>: 97.67%. That means GPS COULD NOT BE USED for over 204 hours. These
are
>: DOD figures presented at the Civil GPS Interface Committee meeting
in
>: Kansas City in Sep of 97.
>
>: Someone in the UK has seen over 30 failures of GPS units that are
kept
>: in a nice safe lab with good antennas on the roof. The figure of
>: 2000 MTBF was thrown out. VOR recivers have 10,000 MTBF.
>
>: So at this point counting on GPS is very risky.
>
>how many dropouts on handheld units were caused by the satellite
system
>and how many were caused by the receiver? dropouts are not NECESSARILY
>caused by the satellite system. i suspect that to keep the costs down
the
>some realiability has been sacrificed. perhaps people are using these
>units for tasks they were never designed to be used for. they are for
>recreation use not precision approaches to runways. they do damn well
for
>the tasks they should be used for at the price they sell for.
>
>--
>regards
>vic fraenckel
Say that again, louder please
Jim Wolper
Marc Rodstein wrote:
> >
> >Jim Wolper <wolp...@isu.edu> wrote in article <34D1E9...@isu.edu>...
> >> A true-life war story with a moral about GPS and
> >> navigation.
> >> snip
>
> Those of you who are using handhelds should not be disappointed with
> GPS outages unless you have an external aircraft antenna. The "antenna
> in the windshield" is always blocked from seeing a portion of the sky
> by the airframe. It is amazing that it works as well as it does, but
> it frequently cannot see enough satellites.
>
> I have an external roof top antenna on 2 different planes, and a 12
> channel GPS-195. I never get outages, not one, in 400 hours of flying
> over 18 months.
The aircraft in question has a good roof top antenna.
I fly about 300 hours a year and see 4 or 5 outages using various systems.
I have been investigating the possibility of terrain blocking GPS signals in
this
incident. (I like trigonometry...) Some of the satellites were rather low
in the sky to the Northwest and Northeast, but I think they were still
above the terrain. However, one of the satellites set during this incident
and I am beginning to think that the WARN light was due to the receiver
switching satellites.
JSW
Keith Arnold
On Fri, 06 Feb 1998 17:20:40 +0000, Jim Wolper <wolp...@cwis.isu.edu>
wrote:
Someone wrote:
>> I have an external roof top antenna on 2 different planes, and a 12
>> channel GPS-195. I never get outages, not one, in 400 hours of flying
>> over 18 months.
>
>The aircraft in question has a good roof top antenna.
>
>I fly about 300 hours a year and see 4 or 5 outages using various systems.
>
>I have been investigating the possibility of terrain blocking GPS signals in
>this
>incident. (I like trigonometry...) Some of the satellites were rather low
>in the sky to the Northwest and Northeast, but I think they were still
>above the terrain. However, one of the satellites set during this incident
>and I am beginning to think that the WARN light was due to the receiver
>switching satellites.
>
>JSW
>
=======>
I'll bet it has something to do with the parallel channel thing. The
195 has 12 channels that receive signal all the time. No switching.
Some have only one channel that switches in rotation, to each satellite
in turn. Could be a problem there.
ô¿ô - Keith - 182L/STOL N3431R - Chino, California
N33° 58' 46" W117° 38' 41"
William LeFebvre
>systems they are putting into cars, though. Cars go under bridges,
>through tunnels, drive down narrow tree-canopy-shrouded roads, and drive
>in urban canyons. All of those sound like places where GPS will have
>trouble working well
FYI: they use a combination of techniques with GPS to cover times when
GPS can't lock on. Depending on the system, they'll use some
combination of wheel motion, magnetic compass, and map matching along
with GPS. Those methods have problems with cumulative error, so the
GPS (when available) is needed to correct long term effect. But yes
there are problems in big urban canyons.
Unlike airplanes, if a car loses its lock on the GPS signal, it isn't
going to crash in to the ground. So it doesn't need to be there
99.99% of the time.
--
William LeFebvre
Group sys Consulting
<w...@groupsys.com>
+1 770 813 3224
Roy Smith
w...@groupsys.com (William LeFebvre) wrote:
> FYI: they use a combination of techniques with GPS to cover times when
> GPS can't lock on. Depending on the system, they'll use some
> combination of wheel motion, magnetic compass, and map matching along
> with GPS.
Interesting. I didn't realize they were so sophisticated. Get a fix when
you can, DR between fixes. Just like real navigation systems :-)
There was a big ship (was it the QE-2?) that went aground off Cape Cod a
few years ago. Turns out they were way off course. The crew has set the
GPS-driven autopilot to steer the ship and goofed off. Unfortunately,
something broke with the GPS sensor and the system went into "drift
mode". This is fine for short gaps, and not a big problem if the crew
notices the alarm and does something about it, but if otto's driving,
somebody's got to be watching otto to make sure he doesn't go crazy, and
nobody was.
lop...@hboi.edu
Gregory Travis wrote:
>
> 1. How do you use GPS underwater
The only limitation is that the antenna has to be on the surface (or
technically just within 1/2 wavelength thereof). The rest is up to your
(our) imaginations.
> 2. What kind of lobby does the "1/100 foot" surveyors
> association have to justify a $500million/year system
> for, what, 10,000 surveyors?
As for question #2, I do not care to get involved in a rhetorical
discussion just to try to inflict others with my opinion (and vice versa)
which is why I quit subscribing to this NG.
-------------------==== Posted via Deja News ====-----------------------
http://www.dejanews.com/ Search, Read, Post to Usenet
Keith Arnold
On 30 Jan 1998 23:30:26 GMT, tho...@not.abnormal.com (Tim Hogard)
wrote:
>Jim Wolper (wolp...@isu.edu) wrote:
>: A true-life war story with a moral about GPS and
>: navigation.
>
>: Now comes the scary part.
>
>: Two miles from the beacon the red WARN light on the GPS went on.
>: It said 1.9NM all the way to touchdown. I believe what
>All it takes to show you how much you can't count on GPS is get a good
>handheld and take it everywhere for a week. I had a 4 failures last
>week.
>
>Last year GPS was usable almost 98% of the time.
>
>
>-tim
=======>
Can't say what you're using but I've used my Garmin 195 in the plane, in
the car with and without the external antenna and NEVER had failures
like you're talking about. I also have a Northstar GPS 60 in my panel
with like results, no problems. Have used the Northstar all over the
West.
Billy Dollarhide
Where is that handheld LORAN with moving map and full North American
database??
Must have left it in my shirt pocket.
Pete wrote:
> In article <34D1E9...@isu.edu>, Jim Wolper <wolp...@isu.edu> wrote:
>
> > A true-life war story with a moral about GPS and
> > navigation.
>
> > Two miles from the beacon the red WARN light on the GPS went on.
> > It said 1.9NM all the way to touchdown. I believe what
> > happened is that as we flew into the valley we had loss of signal
> > due to terrain masking of satellites. Just when I wanted
> > the GPS the most, it failed.
> >
> > We made a safe and legal VFR approach nonetheless; we had
> > the required visibility (even though we couldn't see *&&^$#%$;
> > there are no obstruction lights on the mountains, so even
> > with 10 miles visibility we couldn't see them 5 miles away)
> > and followed the road which we both knew from long experience
> > leads to the runway.
> >
> > The point? As Bowditch says, no prudent navigator relies on
> > any one piece of navigational equipment. Back up that GPS with
> > something, even if it's only dead reckoning. (And while you're
> > at it, back up your hard drive, too.)
>
> A really good story to back up the idea of keeping Loran C operational.
> While the weather could possibly create dicey signal, it seems to me
> having a seamless transitin from one form of radionav to another is a good
> idea. This story will be forwarded to my Congressman, who will be voting
> on continued Loran funding...pete
>
> --
> Surely you"re *smart* enough to remove the spam control...
Steve Peltz
In article <roy-070298...@mcsv29-p7.med.nyu.edu>,
Roy Smith <r...@popmail.med.nyu.edu> wrote:
>Interesting. I didn't realize they were so sophisticated. Get a fix when
>you can, DR between fixes. Just like real navigation systems :-)
It really helps to be able to assume that the car is going to stay on the
road...you know that it is probably not in the middle of the block when it
does that 90 degree turn and keeps going.
Keith Arnold
On Tue, 03 Feb 1998 13:20:14 -0500, r...@popmail.med.nyu.edu (Roy Smith)
wrote:
>wb8...@netcom.com (David Lesher) wrote:
>> You get the time. Most cellular telephone sites use GPS as a time
>> reference. It {I am told} offers orders of magnitude better accuracy
>> than LF/HF WWVB/WWV.
>
>Orders of magnitude better than WWV? That I greatly doubt!
=====>
You're right, Roy. From an ex-metrologist.
Steve Peltz
In article <34e4c40c...@news.jps.net>,
Keith Arnold <kar...@jps.net> wrote:
>On Tue, 03 Feb 1998 13:20:14 -0500, r...@popmail.med.nyu.edu (Roy Smith)
>wrote:
>=====>
>You're right, Roy. From an ex-metrologist.
Unless you're time-correcting WWV for the distance you are from the
station, GPS would have to be more accurate (well, I AM assuming that the
timebase given to the satellites is at least as accurate as WWV). I'm not
sure what an "order of magnitude" was meant to be in that statement -
but if one is off by a few milliseconds and the other is on the order
of a few microseconds, that's a few orders of magnitude right there.
Of course, a cellphone doesn't need accuracy better than 1 second,
I'd think.
David Lesher
pe...@jaka.ece.uiuc.edu (Steve Peltz) writes:
>Of course, a cellphone doesn't need accuracy better than 1 second,
>I'd think.
Cellphones need no time. Cell-site transmitters, on the other hand,
use it for things such as frequency accuracy.....
Keith Arnold
On 14 Feb 1998 15:35:15 -0600, pe...@jaka.ece.uiuc.edu (Steve Peltz)
wrote:
=======>
Keith replied:
Yes, Steve, the time laps for the WWV signal is corrected for. It is
known within ps.
Keith Arnold
On Wed, 4 Feb 1998 17:01:09 GMT, wb8...@netcom.com (David Lesher) wrote:
>
>"We don't pay" here really means "we don't have an option not to
>pay.." If we do not use it; we still pay for it.
======>
Keith replies:
David I tried to E-mail but it got returned. To answer your last to me:
David Lesher wrote:
> > No.
>
> You might use DejaNews and look it up.
> He seems to agree with me...
>
Okay, I'll do that. However, I worked on the GPS program in Rockwell's
Metrology department and we used the signals from WWV to calibrate the
Cesium clocks used in the satellites. Who knows for sure?
Thanks, bye.
Keith Arnold
On 7 Feb 1998 15:43:37 GMT, w...@groupsys.com (William LeFebvre) wrote:
>Unlike airplanes, if a car loses its lock on the GPS signal, it isn't
>going to crash in to the ground. So it doesn't need to be there
>99.99% of the time.
=========>
Keith wrote:
Hey, whoa... You mean that if a GPS in an airplane failes, the plane
will "crash to the ground"?
Gustavo Flores
In article <34ee0923...@news.jps.net> kar...@jps.net (Keith Arnold) writes:
>From: kar...@jps.net (Keith Arnold)
>Subject: Re: GPS in autos (was: "it could happen to you")
>Date: Fri, 20 Feb 1998 22:53:29 GMT
Remember : Aviate , Navigate, Communicate.
It's amazing how much importance people attach to avionics.
Gustavo Flores
tobus
Several years ago, I got checked out at an FBO in Manassas, VA, which is
under one of the rungs of the Dulles Int'l Class B. The rungs are
circular there. The instructor told me that "Unfortunately, this
airplane doesn't have DME, so we can't tell if we're in the TCA."
Good thing they invented moving map displays. I've always wondered if
that kid would claim, after flying into a mountain, that the FAA
should've put a VOR at the peak.
JohnMcGrew
>I believe what happened is that as we flew into the valley we had loss of
>signal due to terrain masking of satellites.
Many units now provide a Sat config screen, so you can tell where the sats are
going to be at a certain place and time, and if they might be obstructed by
known objects.
Of course, who thinks ahead to check that before an approach?
Roy Smith
johnm...@aol.com (JohnMcGrew) wrote:
> Many units now provide a Sat config screen, so you can tell where the sats are
> going to be at a certain place and time, and if they might be obstructed by
> known objects.
>
> Of course, who thinks ahead to check that before an approach?
This is the whole point of RAIM on IFR certified units.
Hank Levine
I just read this posting and could not agree with it more. As a matter of
fact, I recently took my 210
off autopilot and discovered that cross country VFR, I had some difficulty
maintaining +- 200ft,
and +-10 degree heading for extended period. I then learned that I could no
longer
without extreme effort read a sectional chart and find my position after
turning off
my nav equip for 15 minutes.
I'm happy to say that this is no loner the case, but, there is a lesson
here.
Regards:H.L.
--
To reply please delete the "F" in my email address
Pete <just...@a.crl.com> wrote in article > In article
<34D1E9...@isu.edu>, Jim Wolper <wolp...@isu.edu> wrote:
>
> > A true-life war story with a moral about GPS and
> > navigation.
>
> > Two miles from the beacon the red WARN light on the GPS went on.
> > It said 1.9NM all the way to touchdown. I believe what
> > happened is that as we flew into the valley we had loss of signal