GPS Notam ??

luvflyin

luvflyin

Touchdown! Greaser!
Joined
May 8, 2015
Messages
15,787
Location
Santa Barbara, CA
Display Name
Display name:
Luvflyin
What is NAV PSEUDO RANDOM NOISE 16 OUT OF SERVICE. There is another one that has 20 instead of 16.
 
Truly random noise is difficult if not impossible to synthesize so they have to use the pseudo stuff. Besides it's lower in cholesterol and unsaturated fats.
 
BigBadLou said:
I still wouldn't eat it. It's bad for your liver. :(
Click to expand...
Thank you for your concern for my liver....but I haz confusion...what does your consumption choice have to do with my liver?
 
Clark1961 said:
Thank you for your concern for my liver....but I haz confusion...what does your consumption choice have to do with my liver?
Click to expand...
You know what they say: "It's a big world" and "balance in universe" and all that mumbo-jumbo.
What will your liver say if I order a pint of Guinness after work? ;)
And what would you say if the pint was shared? :)
 
Half Fast said:
Okay, but what am I supposed to do with that bit of knowledge?
Click to expand...

Depending on where you are and the time you are there, you may not have enough functioning satellites visible to the GPS device to perform all expected functions.

You should be able to get a position plot, but you may not have enough visible to provided the required fidelity and cross checking required for some or all GPS approaches. Plan on being able to get to your destination and on the ground without GPS.
 
Doggtyred said:
Depending on where you are and the time you are there, you may not have enough functioning satellites visible ...
Click to expand...
Don't you now wish you had memorized that absolutely utterly useless number of satellites required for an accurate GPS position back when you were studying for the written test full of such silly questions? :D
 
BigBadLou said:
Don't you now wish you had memorized that absolutely utterly useless number of satellites required for an accurate GPS position back when you were studying for the written test full of such silly questions? :D
Click to expand...
4 plus waas ground station. End of education.
 
Of course, you also have to have all the sat orbits memorized to know what the GPS constellation is at the time of your flight.
 
I see that notam from time to time, no noticeable change in GPS functionality. I guess be more prepared than normal to switch to alternate nav methods is the point?
 
cowman said:
I see that notam from time to time, no noticeable change in GPS functionality. I guess be more prepared than normal to switch to alternate nav methods is the point?
Click to expand...

Yup. It isn't SUPPOSED to interfere with GPS, but it might.

We've found it in the G1000 telemetry. A 182 isn't really capable of 750 knots ground speed.
 
BigBadLou said:
Then you'd fail that question.
IIRC, they were looking for answer "5" for some strange reason. Though 3 are normally sufficient (hence term "triangulation"). *shrug*
Click to expand...
3 for triangulation but that assumes Flatland. For 3D (altitude) the 4th sat is needed for spherical location. I forget what the 5th is for.
 
Normally 3 points is enough to triangulate even in spherical environment, assuming that your position is not above the geo orbit. :D
(don't forget, the GPS signal has timestamps so the receiver can calculate its distance from the satellites which is slant distance, of course)
 
murphey said:
3 for triangulation but that assumes Flatland. For 3D (altitude) the 4th sat is needed for spherical location. I forget what the 5th is for.
Click to expand...

Error detection. Just because you get an answer doesn't mean the answer is usable.

With an unsynchronized receiver clock (which is how almost all of us operate), 4 satellites will always give you a 3D answer, but you have no idea if that answer is anywhere near your real position.
 
The way I always remembered it was: You need 2 more than the (conventional) number of dimensions you want to operate in.

2D plot, you need 4, 3D plot, you need 5.

The error correction one is what gets everybody :)

Anyway I'm guessing in this situation a RAIM wouldn't help as that wouldn't realize they were going to taken offline? I believe the RAIM check just tells us if enough satellites will be in the correct positions to do the job at a specified point in time and space, not whether they will actually be functional? In which case if one doesn't see the NOTAM then you are in for "Surprise, GPS degradation!".
 
BigBadLou said:
Then you'd fail that question.
IIRC, they were looking for answer "5" for some strange reason. Though 3 are normally sufficient (hence term "triangulation"). *shrug*
Click to expand...
4 plus ground station is 5 . . .which is the correct response.
 
Doggtyred said:
Such things weren't on my written test at the time. But thanks for playing :)
Click to expand...

Haha same here. I had ADF questions. And I think if I'd have done the written years sooner there were even some LORAN ones? Anyone know? LOL
 
ocflyer said:
The way I always remembered it was: You need 2 more than the (conventional) number of dimensions you want to operate in.

2D plot, you need 4, 3D plot, you need 5.

The error correction one is what gets everybody :)

Anyway I'm guessing in this situation a RAIM wouldn't help as that wouldn't realize they were going to taken offline? I believe the RAIM check just tells us if enough satellites will be in the correct positions to do the job at a specified point in time and space, not whether they will actually be functional? In which case if one doesn't see the NOTAM then you are in for "Surprise, GPS degradation!".
Click to expand...
The RAIM prediction would be wrong because it doesn't know about interference. But RAIM itself would still detect the unusable solution when it occurred. I watched a 430 do just that as I started a missed approach near a large surfing event once. I suspect some jerk had a jammer.
 
BigBadLou said:
Cool.
And may I assume that you actually took the real WRITTEN test? Not a "click-here-or-there" test? :)
Click to expand...

Sadly, No... but had I pursued my PPL when I first became interested in aviation in my teens, I very well might have. And had questions on Loran-C
 
MAKG1 said:
The RAIM prediction would be wrong because it doesn't know about interference. But RAIM itself would still detect the unusable solution when it occurred. I watched a 430 do just that as I started a missed approach near a large surfing event once. I suspect some jerk had a jammer.
Click to expand...

Reading this thread the other night I looked and the nearly incomprehensible RAIM prediction website also has map overlay layers for all of the GPS interference NOTAMs on the interactive map.

Of course, when I looked, the entire southern half of the U.S. was covered in the usual NOTAMed rings, so I don't know what use the website is.

The predictions on the site are nearly incomprehensible because they assume certain aspect angles, and half the U.S. was blanketed in NOTAMs saying we're "all going to die".

LOL.

If anyone wants to give lessons on all the options on that website, I'd listen and read. I can't figure out how it works.
 
I don't think I will ever understand why the government puts up this great system for all to use and then they f*** with it. "But we NOTAMed it". So what? WHY do you have to f*** with it? It's working. Let it work. Let us use it. Don't f*** with it. Otherwise airplanes will fall out of sky and hipsters will get lost around the corner from their house. Don't f*** with it, dammit.
 
BigBadLou said:
I don't think I will ever understand why the government puts up this great system for all to use and then they f*** with it. "But we NOTAMed it". So what? WHY do you have to f*** with it? It's working. Let it work. Let us use it. Don't f*** with it. Otherwise airplanes will fall out of sky and hipsters will get lost around the corner from their house. Don't f*** with it, dammit.
Click to expand...

Have to spend that GPS jamming defense contract money somewhere.

- Create satellite system for military and purposefully skew the data for civilians for years.
- People both figure out they'd really like more accuracy and they can get it from differential GPS.
- Turn off Selective Availability. People now have good accuracy.
- Realize it's still not good enough for things like airplane approaches. Build giant nationwide regional accuracy correction/enhancement system, shove that data through a couple of ancient TV satellites that are somewhat useless for anything but low speed data, until some more can be launched.
- Get that all done. Call it WAAS. Yay accuracy.
- Shut down extremely inexpensive and slightly less accurate, but way too easy to make more accurate terrestrial backup system, LORAN. Pretend it was a lot more expensive than it was.
- Start shutting down VORs.
- DoD gets paranoid again about accuracy. Starts multiple contracts in multiple military branches for contractor buddies to make theatre and localized GPS jamming systems.
- Put out never-ending NOTAMs across half of the U.S., and most of the entire southern tier of States that testing could wipe out GPS reception.
- Launch multiple GPS replacement satellites with new encrypted higher accuracy military signals not available to genpop. Also has anti-jamming tech learned by jamming the old system.
- Leave old vulnerable system signals on new satellites because of need for backward compatibility.

- Gather underpants.

- Boeing and Raytheon ... profit. Continually.

LOL. Total cluster**** of big money everywhere.

Don't forget the hipsters also wouldn't be able to play Pokémon Go. ;)
 
luvflyin said:
What is NAV PSEUDO RANDOM NOISE 16 OUT OF SERVICE. There is another one that has 20 instead of 16.
Click to expand...
Ok. It's out of service. If it's one of the 5 I need for that flight than I'm one short. But why the PSUEDO RANDOM NOISE stuff? Is why it's out of service pertinent somehow? What if it said BATTERY DEAD? NUMBER THREE TRANSITIOR TITS UP? CRASHED AND NEEDS REPROGRAMMING?
 
Honestly are you ever in a position where you're only getting 4 sats?

I work in the digital aerial mapping field, and have processed literally thousands of differential GPS solutions. We are entirely dependent on GPS for accuracy with requirements far tighter than you could ever hold shooting an approach (like under 6" horizontal and vertical in the data taken from a plane at 6500'AGL 150kts). I honestly can't remember seeing the airborne drop below 5 satellites other than directly over a military installation, regardless of these NOTAM's all over. Those NOTAM areas do cause "PDOP Spikes" and a poor alignment of the usable satellites from time to time but again that's more a concern for survey quality accuracy than for flying safely.
 
You must log in or register to reply here.
Back
Top