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#1
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GPS PRN NOTAM
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 |
#2
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"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. |
#3
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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 |
#4
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#5
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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 |
#6
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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. |
#7
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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 |
#8
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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 |
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