Hello All,
What does the following NOTAM mean:

GPS 02/001 GPS PRN 26 OTS WEF 0502082100-0502090900

I know it says "GPS Pseudo Random Noise 26 Out of Service" but what are its
implications? Does it mean that RAIM is not available during the outage?

Thanks,

-Ali

"Ali Ghorashi" > wrote in message =
...
> Hello All,
> What does the following NOTAM mean:
>=20
> GPS 02/001 GPS PRN 26 OTS WEF 0502082100-0502090900
>=20
> I know it says "GPS Pseudo Random Noise 26 Out of Service" but what =
are its
> implications? Does it mean that RAIM is not available during the =
outage?
>=20
> -Ali
>
Only the one satellite vehicle (number 26) will be out of service for 12 =
hours.
Your GPS receiver still will compute RAIM over the remaining
constellation of satellites visible to you during the affected hours.

If I were not so lazy, I could look up the vehicle's orbit, and learn
whether SVN26 (PRN26) will even be on your side of the world
during its listed hours of outage.
You'll probably see no adverse effects at all.

Ali Ghorashi wrote:
> Hello All,
> What does the following NOTAM mean:
>
> GPS 02/001 GPS PRN 26 OTS WEF 0502082100-0502090900
>
> I know it says "GPS Pseudo Random Noise 26 Out of Service" but what
are its
> implications? Does it mean that RAIM is not available during the
outage?
>
> Thanks,
>
> -Ali

Maybe, maybe not ;)

It's not at all intuitive what the effect is on RAIM. You can have one
or more OTS and still have RAIM. Or you can have none OTS and still
lose RAIM (although with a fully healthy constellation, the
availability is damn near 100% these days, with 30 operational birds up
there now).

Some handy links:

https://pilotweb.nas.faa.gov/distribution/atcscc.html
https://pilotweb.nas.faa.gov/distribution/home.html


Regards,
Jon

wrote:
> Ali Ghorashi wrote:
>
>>What does the following NOTAM mean:
>>
>>GPS 02/001 GPS PRN 26 OTS WEF 0502082100-0502090900
>>
>>I know it says "GPS Pseudo Random Noise 26 Out of Service" but what
> are its implications? Does it mean that RAIM is not available
> during the outage?
>
> Maybe, maybe not ;)
>
> It's not at all intuitive what the effect is on RAIM. You can have one
> or more OTS and still have RAIM. Or you can have none OTS and still
> lose RAIM (although with a fully healthy constellation, the
> availability is damn near 100% these days, with 30 operational birds up
> there now).

I guess it depends on where you are.
In Oz, I often see in a TAF a few short-duration
holes in RAIM.
eg.

RAIM GPS RAIM PREDICTION 021401
YSBK
02030824 TIL 02030837
02040820 TIL 02040833
02050816 TIL 02050829
GPS RAIM UNAVBL FOR NPA

Thanks for the information. Here's another question:
Since the NOTAM in itself does not convey any useful information, why can't
the FAA's computer do the calculation and show the results in an easily
digestible format? Something like: "GPS navigation may be effected from
xxxxZ to xxxxZ around [location]".

The computer seems to have all the necessary inputs: time of departure, time
enroute, TAS, route, and destination.

-Ali


"Ali Ghorashi" > wrote in message
...
> Hello All,
> What does the following NOTAM mean:
>
> GPS 02/001 GPS PRN 26 OTS WEF 0502082100-0502090900
>
> I know it says "GPS Pseudo Random Noise 26 Out of Service" but what are
its
> implications? Does it mean that RAIM is not available during the outage?
>
> Thanks,
>
> -Ali
>
>

That would require an RFP, receiving budgeting from Congress, then a bid
for the contract, followed by an awarding of the contract, followed by
changes to the contract and increasing the cost of the contract,
followed by delayed delivery... well, you get the idea.

Ali Ghorashi wrote:
> The computer seems to have all the necessary inputs: time of departure, time
> enroute, TAS, route, and destination.

MC wrote:
> wrote:
> > Ali Ghorashi wrote:
> >
> >>What does the following NOTAM mean:
> >>
> >>GPS 02/001 GPS PRN 26 OTS WEF 0502082100-0502090900
> >>
> >>I know it says "GPS Pseudo Random Noise 26 Out of Service" but what
> > are its implications? Does it mean that RAIM is not available
> > during the outage?
> >
> > Maybe, maybe not ;)
> >
> > It's not at all intuitive what the effect is on RAIM. You can have
one
> > or more OTS and still have RAIM. Or you can have none OTS and still
> > lose RAIM (although with a fully healthy constellation, the
> > availability is damn near 100% these days, with 30 operational
birds up
> > there now).
>
> I guess it depends on where you are.
> In Oz, I often see in a TAF a few short-duration
> holes in RAIM.
> eg.
>
> RAIM GPS RAIM PREDICTION 021401
> YSBK
> 02030824 TIL 02030837
> 02040820 TIL 02040833
> 02050816 TIL 02050829
> GPS RAIM UNAVBL FOR NPA


True enough, alth. Some notes to qualify things a little:


- With 1440 minutes in a day, 13 minutes still works out to around
greater than 99%. There's definitely some interesting geometry holes
down in that region though.

- TSO C-129A boxes were stood up prior to SA being turned off, and thus
have a larger sigma value (~33m) hard-coded in there for one of the
error components . This makes things more conservative than the reality
today.

- While the prediction can't account for every possible receiver
manufacturer implementation, the algorithm did follow and was validated
against the RTCA MOPS. Different manufs will get slightly different
availbility (start/end times differ by small margins, edge-of-coverage
cases will have one manuf flag where another may not). We went on the
conservative side there a little. It's a balancing act between
minimizing False Alerts and Missed Detections,

- Rumor has it that Airservices (or maybe CASA) might be experimenting
with a special 129 box which has the updated sigma value. I'd be
willing to bet you'd see most if not all of those short duration
outages disappear.

- The newer 145/146 boxes (whether they're in standalone mode or using
differential corrections) have the updated sigma value. My
understanding is that this was a primary driver for why the manufs
never built a 129 (129B?) box as they couldn't make a business case.
Might as well sell the newer boxes, right?


There are some interesting things are happening this year down under
with your Upper Airspace Program, e.g. ADS-B.


Regards,
Jon

I'm not sure what you mean by the "FAA's computer", but support for
GPS RAIM Prediction and Outage Reporting which went live in November
1995. The information is disseminated to all FSSes (currently 61? I
can't remember exactly... A-76 will result in the consolidation over
the next couple of years). The prediction is for NPA only, so the only
required inputs are destination and time of approach. Only outages
lasting 5 minutes or longer are reported.

I won't touch 'easily digestable' as that could warrant an RFP for an
entire new newsgroup devoted to the subject, let alone another thread
:P


Regards,
Jon