GPS question

alfadog

alfadog

Final Approach
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alfadog
Got this one wrong on a quiz but wondering if the quiz is dated. What is the current status of this? Thanks.

Aircraft should be equipped with an approved and operational alternate means of navigation appropriate to the route being flown. This equipment must be operational but it does not have to be actively monitored unless the RAIM capability of the system fails. The purpose of these backups is to ensure that the aircraft can continue to the destination if something unforeseen occurs to the GPS avionics or GPS constellation.
 
I don't have an answer for you, (I'm also wondering what test it's from.) but I do have an observation.

I find it silly that the legacy navigation systems (VORs, DME, ILS, etc...) which I have occasionally found to be down for maintenance, malfunctioning, or otherwise unavailable for use, are required as "backup" to a system that I have never found to be anything but in perfect working order, and far more accurate.

FAA logic.
 
Rykymus said:
I don't have an answer for you, (I'm also wondering what test it's from.) but I do have an observation.

...
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Online IR rating ground school quiz from American Flyers.
 
I believe that is true for a TSO 129 / 196, non-WAAS box. A TSO 145/146 WAAS is approved for sole source navigation.
 
tsts4 said:
I believe that is true for a TSO 129 / 196, non-WAAS box. A TSO 145/146 WAAS is approved for sole source navigation.
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Just read where the 430W went through a glitch period where it was not OK but that was corrected. The writer was unsure about the 480 WAAS unit, if it was addressed with that unit.
 
alfadog said:
Got this one wrong on a quiz but wondering if the quiz is dated. What is the current status of this? Thanks.

Aircraft should be equipped with an approved and operational alternate means of navigation appropriate to the route being flown. This equipment must be operational but it does not have to be actively monitored unless the RAIM capability of the system fails. The purpose of these backups is to ensure that the aircraft can continue to the destination if something unforeseen occurs to the GPS avionics or GPS constellation.
Click to expand...

Yes, it is dated. The modern rules are that if you have certified WAAS-GPS, you don't need an alternate means of navigation. However, you may want to have that anyway, or at least another independent GPS.

Edit: I believe this is the applicable AC.
 
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alfadog said:
Just read where the 430W went through a glitch period where it was not OK but that was corrected. The writer was unsure about the 480 WAAS unit, if it was addressed with that unit.
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AFAIK the 480 has always been approved for sole source nevigation. I'm not 100% sure about that, but I *am* 100% sure that it is approved as of the software revision that came with my unit, which was 2.3.

Just out of curiosity, what was the nature of the "glitch" that affected the 430W?
 
There was a short period where a service bulletin modded the flight manual supplement rescinding the 480 GPS sole means approval (meaning not much because the 480 like the 430W had a VOR/LOC receiver as well). Of course, for most of us mandatory service bulletins aren't, in fact, mandatory. A software upgrade took care of the issue, but if you never installed the service bulletin, you never really lost the authority for sole means.
 
Rykymus said:
I don't have an answer for you, (I'm also wondering what test it's from.) but I do have an observation.

I find it silly that the legacy navigation systems (VORs, DME, ILS, etc...) which I have occasionally found to be down for maintenance, malfunctioning, or otherwise unavailable for use, are required as "backup" to a system that I have never found to be anything but in perfect working order, and far more accurate.

FAA logic.
Click to expand...

There are still NOTAMs about the military doing interference testing on GPS in the southwest U.S. In addition, ANY navigation equipment can malfunction, so it is always a good idea to have an alternate means of navigation, even an inferior one, whether the rules require it or not.
 
Palmpilot said:
There are still NOTAMs about the military doing interference testing on GPS in the southwest U.S. In addition, ANY navigation equipment can malfunction, so it is always a good idea to have an alternate means of navigation, even an inferior one, whether the rules require it or not.
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I've asked this question before but don't recall if I got an answer. Does anyone know if those interference tests also affect the GLONASS frequencies? As I understand it, some of the newer GPS chips can switch between GPS and GLONASS, or use them in conjunction. Anyone?
 
Rykymus said:
I don't have an answer for you, (I'm also wondering what test it's from.) but I do have an observation.

I find it silly that the legacy navigation systems (VORs, DME, ILS, etc...) which I have occasionally found to be down for maintenance, malfunctioning, or otherwise unavailable for use, are required as "backup" to a system that I have never found to be anything but in perfect working order, and far more accurate.

FAA logic.
Click to expand...

Is the GPS box itself in your panel infallable? Mine's not. I've had two different panel-mounted, IFR-certified GPS boxes fail in flight.

I have also flown in areas where "GPS testing" was going on, which resulted in the loss of GPS capability for the duration of the testing.

Just because it's never happened to you doesn't mean it's never happened.
 
Jim_R said:
Is the GPS box itself in your panel infallable? Mine's not. I've had two different panel-mounted, IFR-certified GPS boxes fail in flight.

I have also flown in areas where "GPS testing" was going on, which resulted in the loss of GPS capability for the duration of the testing.

Just because it's never happened to you doesn't mean it's never happened.
Click to expand...

The G1000 airplane I fly from time to time keeps a record of its maximum ground speed. It's 750 knots. Somehow, I doubt we found a 600 knot tailwind. This is a 182, so it obviously wasn't really supersonic.

So, yes, GPS does fail sometimes. Note that G1000 airplanes have TWO GPS units, so that there is any data at all means that both of them had the same wrong readings. Another GPS is not necessarily adequate redundancy.
 
MAKG1 said:
So, yes, GPS does fail sometimes. Note that G1000 airplanes have TWO GPS units, so that there is any data at all means that both of them had the same wrong readings. Another GPS is not necessarily adequate redundancy.
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Also, it is quite possible for GPS signals to be interfered with by radio sources on the ground. I'm not sure whether they ever caught the joker, but there was someone with a mobile transmitter in the PTK/VLL area causing effective GPS outages during the 2011-2013 time frame. There were "GPS unreliable" NOTAMs published at PTK due to this, including for the RNAV 27 approach. I was never bitten by the problem in actual IFR conditions, but experienced many transient outages during practice over the space of those two years. So yes, it can happen.
 
You can also fake GPS signals: force receiver to think it is somewhere else ... Although, I'm sure you can fake the VOR as well.
 
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